Progestin-Only Pretreatment Enhances Follicular Synchronization and Embryo Development: A Three-Arm Retrospective Cohort Study in GnRH Antagonist IVF Cycles

Progestin-Only Pretreatment Enhances Follicular Synchronization and Embryo Development: A Three-Arm Retrospective Cohort Study in GnRH Antagonist IVF Cycles | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Progestin-Only Pretreatment Enhances Follicular Synchronization and Embryo Development: A Three-Arm Retrospective Cohort Study in GnRH Antagonist IVF Cycles Masato Kobanawa This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6998674/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Hormonal pretreatment prior to controlled ovarian stimulation (COS) in assisted reproductive technology (ART) is widely used to improve follicular synchronization and schedule flexibility. However, the comparative impact of different pretreatment strategies—progestin-only, combined oral contraceptive pills (COCP), and no pretreatment—on follicular dynamics and clinical outcomes remains unclear. Methods: In this retrospective cohort study, 240 patients undergoing their first IVF/ICSI cycle with a GnRH antagonist protocol and recombinant FSH monotherapy were analyzed. Participants were divided into three groups: progestin-only pretreatment (P group), COCP pretreatment (COCP group), and no pretreatment (control group). Baseline characteristics, follicular development, embryo quality, and cumulative reproductive outcomes were compared. Levene’s test was used to assess follicular size variability, and multivariable regression analyses were performed to adjust for confounding variables. Results: The P group demonstrated significantly improved follicular synchronization, as evidenced by the lowest variability in the ratio of follicles ≥ 18 mm to ≥ 14 mm. Embryological outcomes were superior in the P group, with higher oocyte maturation rate (p = 0.040), fertilization rate (p = 0.038), and number of good-quality blastocysts (p = 0.015) compared to the other groups. The blastocyst development rate was also significantly greater (p = 0.029). Although cumulative live birth rate (CLBR) did not reach statistical significance, a trend toward higher CLBR was observed in the P group (87.0%) compared to COCP (72.0%) and control (75.2%). Conclusion: Progestin-only pretreatment leads to superior follicular synchronization and improved embryo developmental potential in GnRH antagonist IVF/ICSI cycles. These benefits may enhance ART efficiency and contribute to improved cumulative outcomes. progestin-only pretreatment combined oral contraceptive pills follicular synchronization in vitro fertilization controlled ovarian stimulation cumulative live birth rate Figures Figure 1 Figure 2 Figure 3 Introduction Hormonal contraceptives have a broad range of indications beyond pregnancy prevention in the field of gynecology. Their use as pretreatment prior to assisted reproductive technologies (ART), particularly in controlled ovarian stimulation (COS), includes menstrual cycle scheduling, synchronization of the oocyte cohort, modulation of the endocrine environment prior to stimulation, and prevention of functional ovarian cyst formation [ 1 ]. The suppressive effects of hormonal contraceptives on follicle-stimulating hormone (FSH) and luteinizing hormone (LH) may facilitate better synchronization of follicular development during COS. Combined oral contraceptive pills (COCPs), which include both estrogen and progestin, strongly suppress the hypothalamic–pituitary–ovarian (HPO) axis. However, concerns have been raised regarding their potential negative impact on follicular growth and endometrial receptivity. In contrast, progestin-only agents (e.g., norethisterone) may suppress GnRH pulsatility with relatively less interference in endogenous hormonal dynamics [ 2 ]. A prospective randomized trial investigating hormonal pretreatment prior to in vitro fertilization (IVF) found that women who received hormonal contraceptives required higher total gonadotropin doses, but this did not adversely affect the number of oocytes retrieved or pregnancy outcomes [ 3 ]. Furthermore, a meta-analysis of four randomized controlled trials (RCTs) concluded that, in GnRH antagonist cycles, women with and without prior hormonal contraceptive pretreatment had comparable ongoing pregnancy rates and oocyte retrieval outcomes [ 4 ]. Thus, the effectiveness of pretreatment prior to COS initiation remains unclear. In particular, few studies have comprehensively compared the effects of COCPs, progestin-only agents, and no pretreatment on hormonal profiles, follicular dynamics, and clinical outcomes—including cumulative pregnancy and live birth rates—in women with normal ovarian response. Therefore, the objective of this study was to investigate whether hormonal pretreatment strategies—including progestin-only agents and combined oral contraceptive pills—have an impact on ART outcomes, by comparing hormone profiles, follicular development, and cumulative reproductive results in GnRH antagonist IVF/ICSI cycles. Material and methods This retrospective cohort study was conducted at Kobanawa Clinic and included 240 ART cycles performed between April 2022 and December 2024. A total of 363 cases were initially screened, and 240 cycles meeting the eligibility criteria were included after applying exclusion criteria. After approval by the Medical Corporation Kobanawa Clinic Ethic Screening Committee, this study was conducted with opt-out disclosure of information. Based on previous studies reporting cumulative live birth rates (CLBR) ranging from 76% to 86%[5], sample size calculation was performed using Cohen’s w for chi-square testing among three independent groups. The resulting effect size was estimated as w ≈ 0.26 (small to medium).[6] Using G*Power version X.X (Heinrich Heine University, Düsseldorf, Germany), with a two-sided significance level of 0.05 and 80% power, the minimum required sample size was calculated to be 108 participants (36 per group).[7] This study included the first ART cycle of each patient who underwent controlled ovarian stimulation (COS) using recombinant FSH (rFSH) monotherapy with either follitropin alfa, beta, or delta. All patients were covered under the Japanese Healthcare Insurance System and were aged ≤42 years. Exclusion criteria included patients who deviated from the prescription guidelines for Follitropin Alfa, Beta and Delta, those who received concurrent concomitant treatment with human menopausal gonadotropin (HMG), urinary FSH (uFSH), clomiphene, or letrozole, and those who had anti-Müllerian hormone (AMH) levels < 1.2 ng/mL, classified as low prognosis (Figure1). Among 363 patients assessed for eligibility, 123 were excluded due to (1) concurrent use of HMG, urinary FSH, clomiphene, or letrozole, or (2) low ovarian reserve, defined as AMH < 1.2 ng/mL. A total of 240 patients were included in the final analysis. They were categorized into three groups based on pretreatment: COCP pretreatment (n = 50), progestin-only pretreatment (P group, n = 77), and no pretreatment (control group, n = 113). This retrospective study included patients who underwent controlled ovarian stimulation (COS) with or without pretreatment using combined oral contraceptive pills (COCP) or progestin-only pretreatment (P). In the COCP and P groups, pretreatment medications were administered for a variable number of days. The duration was determined based on patient preference and clinic scheduling needs The choice of pretreatment was not randomized, but rather based on clinical discretion and patient preference as part of routine care. In COS, daily subcutaneous injections of Follitropin Alfa (Gonal F; Merck BioPharma, Tokyo, Japan) or Follitropin Beta (Foristim, Organon, Osaka, Japan) or Follitropin Delta (Rekovelle; Ferring Pharma, Tokyo) as a mono protocol with rFSH were administered starting on days 1-3 of menstruation, using the COS with GnRH antagonist protocol. The starting dose of follitropin alfa and beta was determined using the gonadotropin starting dose calculator developed by Kobanawa with a fixed dose. [8] The daily individualized dose of follitropin delta was determined using the serum anti-Müllerian hormone (AMH) level within the previous 12 months and body weight, with a fixed dose used throughout the stimulation.[9] Gonadotropin-releasing hormone antagonists (Ganirest; MSD, Tokyo, Japan) were started at a dose of 0.25 mg/day when the primary follicle reached approximately 14 mm. When several leading follicles reached 17–20 mm, gonadotropins and GnRH antagonist doses of 0.25 mg/day were terminated, and on the same day or the next day, 250 μg of choriogonadotropin alfa was administered. Oocyte retrieval was performed 36-39 hours after triggering. After oocyte retrieval, insemination and intracytoplasmic sperm injection (ICSI) were performed. Then, fertilized oocytes were cultured to blastocysts, which were then frozen. Thawed embryos were transferred during the next menstrual cycle or later by hormone replacement cycles (HRCs) or natural cycles (NCs). In HRC, hormone replacement of estrogen (Estrana Tapes, Hisamitsu Pharmaceutical, Tokyo) at 0.72 mg ×4 every other day was started on days 1-3 of menstruation. With endometrial thickening confirmed to be at least 7 mm, progesterone (UTROGESTAN; Fuji Pharma Co.,Ltd., Tokyo) 200 mg ×3/day was commenced, and blastocyst transfer was performed six days later (P+5). We performed a single embryo transfer (SET). In the NC group, blastocysts were transferred on the fifth day after natural ovulation without the use of drugs. Clinical pregnancy was defined as a case in which the fetal sac was confirmed by transvaginal ultrasonography within four to five weeks of gestation determined from the day of embryo transfer. After pregnancy, birth outcomes were tracked based on reports from the patients or the hospitals where the delivery occurred Blood samples were collected during the study to assess AMH, FSH, luteinizing hormone (LH), estradiol, and progesterone levels. AMH concentrations were measured during screening before the start of the cycle and used to determine the starting dose of gonadotropins. AMH levels were measured using an automated Elecsys AMH assay (Roche Diagnostics, Basel, Switzerland). Serum samples were used to assess endocrine parameters (FSH, LH, estradiol, and progesterone). Mature oocytes (MII) were defined as oocytes confirmed by denudation for intracytoplasmic sperm injection (ICSI) or oocytes confirmed zygotes with two pronuclei by insemination (conventional IVF). The fertilization rate was defined as the number of pronuclei confirmed per insemination by IVF or ICSI punctures. The embryo culture results were compared based on blastocyst rates, defined as the number of high-quality blastocysts (Gardner’s classification of 3BB or higher) per cultured embryo.[10] Clinical pregnancy was defined as a case in which the fetal sac was confirmed by transvaginal ultrasonography within four to five weeks of gestation determined from the day of embryo transfer. After pregnancy, birth outcomes were tracked based on reports from the patients or the hospitals where the delivery occurred Cumulative pregnancy and live birth rates were calculated as the probability of a single-cycle embryo leading to pregnancy or live birth over multiple transfers.[11] The primary outcome of this study was the cumulative live birth rate (CLBR) per cycle according to each pretreatment strategy. For baseline patient characteristics, numerical variables were compared among the three groups using one-way analysis of variance (ANOVA), while categorical variables were compared using the chi-square test. To assess clinical outcomes, multivariable analyses were conducted to adjust for potential confounders identified as significantly different among the groups at baseline. Specifically, multiple linear regression and logistic regression analyses were performed, incorporating these covariates to compare the three groups. To evaluate the variability in follicular size synchronization, Levene’s test was used to compare the homogeneity of variance among groups. All statistical analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). EZR is a modified version of the R Commander designed to provide additional statistical functions frequently used in biostatistics.[12] Results Baseline characteristics were compared among the three groups: COCP, Control, and Progesterone (P) (Table.1). Variable COCP Control P p-value n 50 113 77 Duration of medication (days) 13.52 (3.25) 0 (0) 9.87 (0.75) <0.001 Age, years 32.82 (3.90) 34.39 (3.68) 32.79 (3.90) 0.006 AMH, ng/ml 4.45 (3.06) 4.17 (2.70) 4.37 (2.80) 0.814 AFC, follicles 15.56 (6.43) 16.41 (6.38) 17.17 (7.11) 0.407 Basal E2, pg/ml 35.53 (21.36) 67.65 (392.89) 25.34 (16.09) 0.538 Basal FSH, IU/L 7.60 (2.17) 6.97 (1.61) 6.68 (1.70) 0.017 Basal LH, IU/L 7.88 (3.40) 6.02 (2.22) 6.37 (3.03) <0.001 Body weight, kg 64.97 (53.53) 57.62 (10.99) 58.89 (11.99) 0.253 Gonadotropin.preparation: Follitropin alfa, n (%) 27 (54.0) 58 (51.3) 43 (55.8) 0.97 Gonadotropin.preparation: Follitropin beta, n (%) 2 (4.0) 6 (5.3) 3 (3.9) Gonadotropin.preparation: Follitropin delta, n (%) 21 (42.0) 49 (43.4) 31 (40.3) Trigger.methods: GnRH, n (%) 47 (94.0) 94 (83.2) 65 (84.4) 0.172 Trigger.methods: hCG, n (%) 3 (6.0) 19 (16.8) 12 (15.6) Fertilization.methods: c-IVF, n (%) 44 (88.0) 78 (69.0) 65 (84.4) 0.007 Fertilization.methods: ICSI, n (%) 6 (12.0) 35 (31.0) 12 (15.6) Table.1 Baseline characteristics and treatment parameters of the three groups. Numerical variables are presented as mean (standard deviation), and categorical variables as number (percentage). Statistical comparisons among the COCP, Control, and Progesterone groups were performed using one-way ANOVA for numerical variables and chi-square tests for categorical variables. There were significant differences in patient age ( p = 0.006), basal FSH ( p = 0.017), and basal LH levels ( p < 0.001) among the groups. The duration of medication also varied significantly, with the COCP group having the longest mean duration (13.52 ± 3.25 days) and the Control group having none due to lack of pretreatment ( p < 0.001). However, there was no significant difference in duration between the COCP and P groups, suggesting comparable exposure to pretreatment medications within those two groups. The proportion of fertilization methods differed significantly among groups ( p = 0.007), with the COCP and Progesterone groups showing a higher rate of conventional IVF compared to the Control group. Other variables, including AMH, AFC, basal estradiol, body weight, gonadotropin preparation type, and trigger method, did not show statistically significant differences between groups (Table.1). Based on these results, age, basal FSH, basal LH, and fertilization method were considered potential confounding factors and were included as covariates in subsequent multivariable analyses. Compared to the COCP and control groups, the P group demonstrated significantly higher values in several key embryological outcomes. Specifically, the oocyte maturation rate ( p = 0.040), fertilization rate ( p = 0.038), and the number of good-quality blastocysts ( p = 0.015) were all significantly greater in the P group after adjustment for confounding factors. In addition, the blastocyst development rate was also significantly improved ( p = 0.029) (Table.2). Table.2 Comparison of ovarian stimulation characteristics, embryological outcomes, and clinical outcomes among the COCP, Control, and P groups. Variable COCP Control P Univariate P-value Multivariate P-value Stimulation days, days 13.54 (2.13) 13.49 (3.00) 14.39 (2.97) 0.079 0.078 Maximum follicle diameter on days 6–8 of stimulation, mm 16.7 (3.77) 16.05 (3.09) 16.39 (3.55) 0.51 0.513 minimum follicle diameter on days 6–8 of stimulation, mm 9.12 (1.76) 9.57 (2.08) 9.22 (2.67) 0.398 0.256 Follicle count ≥14 mm on the day of trigger, folllicles 16.96 (6.04) 17 (6.51) 17.47 (7.52) 0.876 0.780 Follicle count ≥16 mm on the day of trigger, folllicles 14.3 (5.23) 15.15 (6.08) 15.03 (7.18) 0.72 0.359 Follicle count ≥18 mm on the day of trigger, folllicles 10.44 (4.57) 11.26 (5.25) 12.34 (5.87) 0.132 0.197 Follicle count ≥20 mm on the day of trigger, folllicles 6.24 (4.19) 6.45 (4.78) 6.58 (4.93) 0.922 0.899 Total gonadotropin dosage, mcg 141.86 (57.35) 148.89 (74.10) 135.55 (51.57) 0.37 0.890 E2 level on the day of trigger, pg/ml 3880.98 (1615.67) 3889.8 (2076.56) 3994.14 (2606.07) 0.939 0.853 P4 level on the day of trigger, ng/ml 1.67 (2.38) 1.43 (0.82) 1.28 (0.93) 0.278 0.342 Number of oocytes retrieved, oocytes 14.94 (6.02) 16.03 (6.66) 16.43 (7.21) 0.466 0.736 Follicular Output Rate (FORT), No. follicles≧16mm /AFC 1.00 (0.42) 0.98 (0.38) 0.96 (0.50) 0.82 0.712 Follicle-to-Oocyte Index (FOI), No.oocytes/ AFC 0.98 (0.14) 0.97 (0.12) 0.95 (0.12) 0.487 0.470 Ovarian Sensitivity Index (OSI), oocytes/mcg 0.12 (0.06) 0.14 (0.10) 0.15 (0.14) 0.301 0.453 Number of mature oocytes, oocytes 14.56 (6.00) 15.36 (6.71) 16.16 (7.20) 0.421 0.803 Oocyte maturation rate, % 97.00 (6.00) 95.00 (8.00) 98.00 (5.00) 0.022 0.040 Number of two-pronuclei (2PN) zygotes, zygotes 8.38 (4.15) 10.05 (5.43) 10.66 (5.07) 0.044 0.160 Fertilization rate, % 58.00 (20.00) 66.00 (21.00) 67.00 (15.00) 0.028 0.038 Number of good-quality blastocysts, blastocysts 4.92 (3.10) 6.00 (4.02) 7.23 (4.22) 0.005 0.015 Blastocyst development rate, % 57.00 (22.00) 59.00 (22.00) 66.00 (21.00) 0.039 0.029 Number of embryo transfers, transfers 1.84 (1.28) 1.57 (0.99) 1.51 (0.88) 0.177 0.202 Cumulative pregnancy rate, % (n) 86 (43) 85 (96) 97.4(75) 0.01 0.090 Cumulative live birth rate, % (n) 72 (36) 75.2 (85) 87 (67) 0.0726 0.237 Data are presented as mean (standard deviation) for continuous variables or number (percentage) for categorical variables. Univariate p -values were calculated using one-way ANOVA or chi-square tests, as appropriate. For multivariable analysis, age, basal FSH, and basal LH were included as covariates for outcomes up to oocyte retrieval. For outcomes following fertilization, fertilization methods was additionally included as a confounding factor. Furthermore, although not reaching statistical significance in the multivariable analysis, the P group showed a trend toward a higher cumulative live birth rate (87.0%) compared with the COCP (72.0%) and control groups (75.2%) ( p = 0.237), as well as a higher cumulative pregnancy rate ( p = 0.090) (Table.2). In addition, the effect of pretreatment on follicular synchronization was evaluated by comparing follicular size distribution among the three groups. To assess the consistency of follicular synchronization patterns across different pretreatment groups, we evaluated the within-group variability of the proportions of follicles ≥20mm, ≥18mm, and ≥16mm relative to follicles ≥14mm. Three indices of dispersion were calculated within each group: standard deviation (SD), variance (Var), and interquartile range (IQR). Among the three groups—P group (progestin-only pretreatment), COCP group (combined oral contraceptive pills), and control group (no pretreatment)—the P group consistently showed the smallest values for all three dispersion measures (Table.3). Table.3 Within-group variability in follicle size ratios (≥20mm, ≥18mm, ≥16mm per ≥14mm) across pretreatment groups. Pretreatment Group SD (20mm/14mm) Var (20mm/14mm) IQR (20mm/14mm) SD (18mm/14mm) Var (18mm/14mm) IQR (18mm/14mm) SD (16mm/14mm) Var (16mm/14mm) IQR (16mm/14mm) P 0.230 0.053 0.310 0.219 0.048 0.300 0.140 0.019 0.231 COCP 0.249 0.062 0.335 0.254 0.064 0.326 0.145 0.021 0.246 Control 0.239 0.057 0.338 0.193 0.037 0.255 0.130 0.017 0.200 Standard deviation (SD), variance (Var), and interquartile range (IQR) were calculated for each group: P group (progestin-only pretreatment), COCP group (combined oral contraceptive pills), and Control group (no pretreatment). To formally assess whether the P group had significantly lower variability compared to the COCP and control groups, levene’s test was used to compare intra-group variability in follicle size synchronization, as measured by the ratios of follicles ≥20 mm, ≥18 mm, and ≥16 mm to those ≥14 mm. The analysis revealed that only the 18mm/14mm ratio showed a statistically significant difference in variance across pretreatment groups (p = 0.0001), while the 20mm/14mm and 16mm/14mm ratios did not (p = 0.4809 and p = 0.3710, respectively) (Table 4). Table.4 Results of Levene’s tests comparing variance in follicle size synchronization ratios among the three pretreatment groups Ratio Type Overall Levene Test p-value 20mm / 14mm 0.4809 18mm / 14mm 0.0001 16mm / 14mm 0.3710 Comparison Levene Statistic p-value Control vs P 5.353 0.0218 Control vs COCP 6.606 0.0111 P vs COCP 18.947 <0.0001 To further explore this difference, post hoc pairwise Levene’s tests were performed for the 18mm/14mm ratio. The P group showed significantly lower variance than both the Control (p = 0.0218) and COCP groups (p < 0.0001), while the Control group also had significantly lower variance than the COCP group (p = 0.0111) (Table 4). To visually assess differences in follicle synchronization, the 18mm/14mm ratio was plotted by group using boxplots (Figure.2). Boxplots demonstrate inter-group differences in variability. The P group demonstrated the least variability, as shown by the tight distribution and narrow interquartile range. In contrast, the COCP group exhibited the greatest variability, with a broader range and higher dispersion of individual values. These visual findings align with the statistical results from Levene’s test (p = 0.0001), further supported by post hoc analyses showing significant variance differences between all group pairs. Logistic regression analysis was performed to identify factors associated with achieving a ratio of ≥60% for follicles ≥18 mm relative to those ≥14 mm (18/14 ratio). The independent variables included pretreatment group (P vs COCP, P vs control), basal FSH, basal LH, age, and gonadotropin type. The analysis revealed that the P group was significantly associated with a higher probability of achieving an 18/14 ratio ≥60%, compared to the COCP group (OR: 2.34, 95% CI: 1.04–5.28, P = 0.040). No significant difference was observed between the P group and the control group (OR: 1.22, 95% CI: 0.59–2.52, P = 0.59). (Figure.3) The analysis included pretreatment group (P vs COCP, P vs control), age, basal FSH, basal LH, and gonadotropin type. Discussion In this study, we evaluated the impact of different pretreatment strategies—P group, COCP group, and control group—on IVF/ICSI outcomes using a GnRH antagonist protocol. The results revealed that the P group showed a trend toward higher cumulative pregnancy and live birth rates compared with the other groups, along with significantly improved follicular synchronization. When using the ratio of follicles ≥18 mm to those ≥14 mm (18/14 ratio) as a proxy for synchrony, the P group exhibited the highest values and the lowest intra-group variability, suggesting a more uniform follicular cohort. Additionally, the P group demonstrated significantly higher numbers of good-quality blastocysts and higher blastocyst development rates, indicating improved embryo developmental efficiency. These findings may be explained by the influence of progestin on endogenous hormonal dynamics. Progestin pretreatment has been shown to suppress GnRH pulsatility, thereby reducing FSH and LH secretion [13–15]. It also limits early follicular sensitivity to FSH, preventing premature recruitment and contributing to synchronized follicular development [16,17]. Mechanistically, these effects may be mediated via progesterone’s action on hypothalamic kisspeptin neurons. Kisspeptin is a potent activator of the hypothalamic–pituitary–gonadal axis, stimulating GnRH secretion and, in turn, FSH and LH release [18–20]. Nearly all arcuate nucleus (ARC) kisspeptin neurons express progesterone receptors, and the surge in progesterone levels following ovulation suppresses LH secretion via these pathways [21,22]. Furthermore, kisspeptin has been shown to inhibit the upregulation of FSH receptor (FSHR) expression in granulosa cells [23]. Thus, while LH surges are effectively prevented, FSH is not excessively suppressed; instead, follicular sensitivity to FSH is attenuated, suppressing early follicular recruitment prior to menses. This mechanism likely contributes to more synchronized follicle development at the onset of COS. In contrast, COCPs contain ethinyl estradiol (EE), which acts to suppress endogenous gonadotropin release [24–26] and upregulate progesterone receptor expression, thereby potentiating progestin effects [27]. However, excessive suppression of endogenous gonadotropins with COCPs may delay stimulation onset, blunt E2 rise, and increase the duration and total dose of gonadotropins required [3]. Both P and COCP pretreatment may reduce the risk of functional ovarian cyst formation, a frequent issue in reproductive-aged women. In large cross-sectional studies, ovarian cysts larger than 30 mm were found in 4–7% of women undergoing baseline ultrasonography before hormonal contraception initiation [28]. These cysts have been associated with poor ovarian response in IVF cycles, particularly when measuring 30–60 mm [29–31]. Several studies have reported that pretreatment with oral contraceptives reduces the incidence of functional ovarian cysts [32], and this effect is particularly evident with progestins [33]. Therefore, prevention of cyst formation may be another contributing factor to improved follicular synchronization at the start of COS. While some retrospective studies have associated hormonal contraceptive pretreatment with reduced live birth rates after fresh transfer (42.6% vs. 52.8%, P<.001) and lower cumulative live birth rates (62.8% vs. 67.6%, P=.01) [34], a 2017 Cochrane review of 29 RCTs in GnRH agonist and antagonist cycles found that pretreatment with hormonal contraception may reduce the risk of pregnancy loss [33]. However, other RCTs have shown no significant effect on clinical pregnancy or cumulative live birth rates when hormonal contraception was administered for 12–30 days with a 5-day washout period [35]. In our study, the P group showed significantly higher fertilization rates and blastocyst formation rates, which translated into an increased number of viable embryos per cycle. This enhanced oocyte-to-blastocyst efficiency likely contributed to the trend toward higher cumulative pregnancy and live birth rates in the P group. These results highlight the importance of optimizing follicular dynamics to improve embryological outcomes and overall ART success. The superiority of the P group may also be linked to baseline LH levels. Persistently elevated LH during the follicular phase can trigger premature meiotic resumption, oocyte nuclear damage, and apoptosis [37,38]. High LH also promotes excess androgen production by stimulating theca cells, leading to hyperandrogenism [39]. Elevated androgen concentrations in follicular fluid can disrupt intracellular calcium oscillations in oocytes, impeding cytoplasmic maturation and meiotic competence [40]. Oocytes retrieved under high LH conditions may exhibit excessive fragmentation and asymmetric cleavage, with negative implications for fertilization and embryo development [41]. In our study, the COCP group had significantly higher basal LH levels than the control and P groups. This may reflect the lower doses of progestin in COCP formulations (e.g., norgestrel 0.5 mg or levonorgestrel 0.09 mg), compared to the higher-dose norethisterone (5 mg) used in the P group [42]. Therefore, the P group may have benefited from stronger suppression of LH and androgens, resulting in the retrieval of higher-quality oocytes and better embryo development. Taken together, our findings suggest that progestin-only pretreatment leads to superior follicular synchronization, lower LH exposure, and improved embryo developmental potential. These advantages may ultimately enhance ART efficiency, particularly by increasing the number of transferable embryos and improving the likelihood of achieving pregnancy and live birth per cycle. Abbreviations AFC: Antral Follicle Count AMH: Anti-Müllerian Hormone ANOVA: Analysis of Variance ARC: Arcuate Nucleus ART: Assisted Reproductive Technology CLBR: Cumulative Live Birth Rate COCP: Combined Oral Contraceptive Pills COS: Controlled Ovarian Stimulation E2: Estradiol EE: Ethinyl Estradiol ET: Embryo Transfer FSH: Follicle-Stimulating Hormone FSHR: Follicle-Stimulating Hormone Receptor GnRH: Gonadotropin-Releasing Hormone HMG: Human Menopausal Gonadotropin HPO: Hypothalamic–Pituitary–Ovarian HRC: Hormone Replacement Cycle ICSI: Intracytoplasmic Sperm Injection IQR: Interquartile Range IVF: In Vitro Fertilization LH: Luteinizing Hormone MII: Metaphase II Oocyte NC: Natural Cycle OR: Odds Ratio RCT: Randomized Controlled Trial SD: Standard Deviation SET: Single Embryo Transfer rFSH: Recombinant Follicle-Stimulating Hormone Declarations Ethics declarations Ethics approval and consent to participate Our study was approved by the Medical Corporation Kobanawa Clinic Ethic Screening Committee (202311164) and in accordance with the Helsinki declaration. Consent for publication Not applicable Competing interests The authors declare that they have no competing interest. Funding The authors received no specific funding for this work. Authors' contributions Masato Kobanawa: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing–original draft, and Writing–review & editing Availability of data and materials The datasets supporting the findings of this study are available from the corresponding author upon reasonable request. Acknowledgments We express special gratitude to Editage (www.editage.com) for English language editing. References ACOG Practice Bulletin No. 110: noncontraceptive uses of hormonal contraceptives. Obstet Gynecol 2010;115:206–18. D'Arpe S, Di Feliciantonio M, Candelieri M, Franceschetti S, Piccioni MG, Bastianelli C. Ovarian function during hormonal contraception assessed by endocrine and sonographic markers: a systematic review. Reprod Biomed Online. 2016;33(4):436-448. Cédrin-Durnerin I, Bständig B, Parneix I, Bied-Damon V, Avril C, Decanter C, et al. Effects of oral contraceptive, synthetic progestogen or natural estrogen pre-treatments on the hormonal profile and the antral follicle cohort before GnRH antagonist protocol. Hum Reprod 2007;22:109–16. Griesinger G, Venetis CA, Marx T, Diedrich K, Tarlatzis BC, Kolibianakis EM. Oral contraceptive pill pretreatment in ovarian stimulation with GnRH antagonists for IVF: a systematic review and meta-analysis. Fertil Steril 2008;90: 1055–63. Kobanawa M, Iwami N, Hanaoka M, Enatsu K, Ichiyama T. Cost-Effectiveness and Clinical Outcomes of Controlled Ovarian Stimulation With Follitropin Delta and Follitropin Alfa: A Retrospective Study. Cureus. 2024;16(12):e76371. Cohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum Associates Kang H. Sample size determination and power analysis using the G*Power software. J Educ Eval Health Prof. 2021;18:17. Kobanawa M. The gonadotropins starting dose calculator, which can be adjusted the target number of oocytes and stimulation duration days to achieve individualized controlled ovarian stimulation in Japanese patients. Reprod Med Biol. 2023;22(1):e12499. Iliodromiti S, Salje B, Dewailly D, et al.: Non-equivalence of anti-Müllerian hormone automated assays-clinical implications for use as a companion diagnostic for individualised gonadotrophin dosing. Hum Reprod. 2017;32:1710-5. Gardner DK, Schoolcraft WB: Culture and transfer of human blastocysts. Curr Opin Obstet Gynecol. 1999;11:307-11. Maheshwari A, McLernon D, Bhattacharya S: Cumulative live birth rate: time for a consensus?. Hum Reprod. 2015;30:2703-7. Kanda Y. Investigation of the freely available easy-to-use software ‘EZR’ for medical statistics. Bone Marrow Transplant. 2013; 48(3): 452–458. Lesoon LA, Mahesh VB. Stimulatory and inhibitory effects of progesterone on FSH secretion by the anterior pituitary. J Steroid Biochem Mol Biol. 1992;42(5):479-491. Richter TA, Robinson JE, Evans NP. Progesterone blocks the estradiol-stimulated luteinizing hormone surge by disrupting activation in response to a stimulatory estradiol signal in the ewe. Biol Reprod. 2002;67(1):119-125. Skinner DC, Evans NP, Delaleu B, Goodman RL, Bouchard P, Caraty A. The negative feedback actions of progesterone on gonadotropin-releasing hormone secretion are transduced by the classical progesterone receptor. Proc Natl Acad Sci U S A . 1998;95(18):10978-10983. Obruca A, Korver T, Huber J, Killick SR, Landgren B, Struijs MJ. Ovarian function during and after treatment with the new progestagen Org 30659. Fertil Steril. 2001;76(1):108-115. Heikinheimo O, Gordon K, Williams RF, Hodgen GD. Inhibition of ovulation by progestin analogs (agonists vs antagonists): preliminary evidence for different sites and mechanisms of actions. Contraception. 1995; 53:55–64. Pinilla L, Aguilar E, Dieguez C, Millar RP, Tena-Sempere M. Kisspeptins and Reproduction: Physiological Roles and Regulatory Mechanisms. Physiol Rev (2012) 92(3):1235–316. Messager S, Chatzidaki EE, Ma D, Hendrick AG, Zahn D, Dixon J, et al. Kisspeptin Directly Stimulates Gonadotropin-Releasing Hormone Release via G Protein-Coupled Receptor 54. Proc Natl Acad Sci USA (2005) 102(5):1761–6. Hrabovszky E. Neuroanatomy of the Human Hypothalamic Kisspeptin System. Neuroendocrinology (2014) 99(1):33–48. He W, Li X, Adekunbi D, Liu Y, Long H, Wang L, et al. Hypothalamic Effects of Progesterone on Regulation of the Pulsatile and Surge Release of Luteinising Hormone in Female Rats. Sci Rep (2017) 7(1):8096. Clarkson J, d'Anglemont de Tassigny X, Moreno AS, Colledge WH, Herbison AE. Kisspeptin-GPR54 Signaling is Essential for Preovulatory Gonadotropin-Releasing Hormone Neuron Activation and the Luteinizing Hormone Surge. J Neurosci Off J Soc Neurosci (2008) 28(35):8691–7. Fernandois D, Na E, Cuevas F, Cruz G, Lara HE, Paredes AH. Kisspeptin is involved in ovarian follicular development during aging in rats. J Endocrinol. 2016;228(3):161-170. Goldzieher JW, Stanczyk FZ. Oral contraceptives and individual variability of circulating levels of ethinyl estradiol and progestins. Contraception. 2008;78(1):4-9. Ziegler D, Jaaskelainen AS, Brioschi PA, Fanchin R, Bulletti C. Synchronization of endogenous and exogenous FSH stimuli in controlled ovarian hyperstimulation (COH). Human Reproduction 1998;13(3):561‐4. Nestour E, Marraoui J, Lahlou N, Roger M, Ziegler D, Bouchard P. Role of estradiol in the rise in follicle‐stimulating hormone levels during the luteal‐follicular transition. Journal of Clinical Endocrinology and Metabolism 1993;77(2):439‐42. Wright AA, Fayad GN, Selgrade JF, Olufsen MS. Mechanistic model of hormonal contraception. PLoS Comput Biol. 2020;16(6):e1007848. Teichmann AT, Brill K, Albring M, Schnitker J, Wojtynek P, Kustra E. The influence of the dose of ethinylestradiol in oral contraceptives on follicle growth. Gynecol Endocrinol 1995;9:299–305. Thatcher SS, Jones E, DeCherney AH. Ovarian cysts decrease the success of controlled ovarian stimulation and in vitro fertilization. Fertil Steril 1989;52: 812–6. Keltz MD, Jones EE, Duleba AJ, Polcz T, Kennedy K, Olive DL. Baseline cyst formation after luteal phase gonadotropin-releasing hormone agonist administration is linked to poor in vitro fertilization outcome. Fertil Steril 1995;64:568–72. Segal S, Shifren JL, Isaacson KB, Leykin L, Chang Y, Pal L, et al. Effect of a baseline ovarian cyst on the outcome of in vitro fertilization-embryo transfer. Fertil Steril 1999;71:274–7. Biljan MM, Mahutte NG, Dean N, Hemmings R, Bissonnette F, Tan SL. Effects of pretreatment with an oral contraceptive on the time required to achieve pituitary suppression with gonadotropin-releasing hormone analogues and on subsequent implantation and pregnancy rates. Fertil Steril. 1998;70(6):1063-1069. Farquhar C, Rombauts L, Kremer JA, Lethaby A, Ayeleke RO. Oral contraceptive pill, progestogen or oestrogen pretreatment for ovarian stimulation protocols for women undergoing assisted reproductive techniques. Cochrane Database Syst Rev 2017;5:CD006109. Lu Y, Wang Y, Zhang T, Wang G, He Y, Lindheim SR, et al. Effect of pretreatment oral contraceptives on fresh and cumulative live birth in vitro fertilization outcomes in ovulatory women. Fertil Steril 2020;114:779–86. Montoya-Botero P, Martinez F, Rodríguez-Purata J, Rodríguez I, Coroleu B, Polyzos NP. The effect of type of oral contraceptive pill and duration of use on fresh and cumulative live birth rates in IVF/ICSI cycles. Hum Reprod 2020; 35:826–36. Huirne JA, van Loenen AC, Donnez J, et al. Effect of an oral contraceptive pill on follicular development in IVF/ICSI patients receiving a GnRH antagonist: a randomized study. Reprod Biomed Online. 2006;13(2):235-245. Franks S, Stark J, Hardy K. Follicle dynamics and anovulation in polycystic ovary syndrome. Hum Reprod Update 2008;14:367–78. Filicori M, Cognigni GE, Ciampaglia W. Effects of LH on oocyte yield and developmental competence. Hum Reprod 2003;18:1357–8. Nelson VL, Qin KN, Rosenfield RL, et al. The biochemical basis for increased testosterone production in theca cells propagated from patients with polycystic ovary syndrome. J Clin Endocrinol Metab 2001;86:5925–33. Tesarik J, Mendoza C. Direct non-genomic effects of follicular steroids on maturing human oocytes: oestrogen versus androgen antagonism. Hum Reprod Update 1997;3:95–100. Stanger JD, Yovich JL. Reduced in-vitro fertilization of human oocytes from patients with raised basal luteinizing hormone levels during the follicular phase. Br J Obstet Gynaecol. 1985;92(4):385-393. Schindler AE, Campagnoli C, Druckmann R, et al. Classification and pharmacology of progestins. Maturitas. 2003;46 Suppl 1:S7-S16. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6998674","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":479152607,"identity":"534c9dc0-7bdb-436a-8979-af829a989c6b","order_by":0,"name":"Masato Kobanawa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAElEQVRIiWNgGAWjYBADAwYJCEMORBx4QEj9ASQtxmCBBFK0JDaASHxadNuPP/z8oYLBmF+6+dmDn2126fPDDj8E2mInp9uAXYvZmRxjiQNnGMwk5xwzN+xtS87deDvNAKgl2djsAA4tB3IYJA62MdgY3Egwk+Ddxpy7cXYCSMuBxG24tJx//vgHREv6N8m/2+rTDWenf8CvBWQ4UIuZwY0cM2nebYcT5KVzCNhy442ZxZkzEsaSc86UScv+O264QTqn4ECCAR6/nE9/fKOiwsawX7p9m+SbM9Xy8rPTN3/4UGEnh0sLFEggmAZglQZ4laMB+QZSVI+CUTAKRsFIAACstmVAihiwXgAAAABJRU5ErkJggg==","orcid":"","institution":"Kobanawa Clinic","correspondingAuthor":true,"prefix":"","firstName":"Masato","middleName":"","lastName":"Kobanawa","suffix":""}],"badges":[],"createdAt":"2025-06-28 15:23:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6998674/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6998674/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85992173,"identity":"423b1309-ff37-46c6-bac3-f3651afeaf40","added_by":"auto","created_at":"2025-07-04 05:31:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":50728,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6998674/v1/9f9be424ee48e136ab98d2c8.png"},{"id":85992176,"identity":"37f7ecbc-58a5-4a37-b3f6-38050af26722","added_by":"auto","created_at":"2025-07-04 05:31:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":38002,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6998674/v1/148d1fb7b87a8dc2dc9a11d4.png"},{"id":85992174,"identity":"dab228b9-9e1f-4fcb-aa03-5675ba481d73","added_by":"auto","created_at":"2025-07-04 05:31:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":50064,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6998674/v1/2758221705e67c5114072606.png"},{"id":85995185,"identity":"ea6e3ad8-05e7-4ed3-b8b7-ea8f045d182e","added_by":"auto","created_at":"2025-07-04 05:55:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":725951,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6998674/v1/f056c613-6395-457d-915a-9a1ea730dbaf.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Progestin-Only Pretreatment Enhances Follicular Synchronization and Embryo Development: A Three-Arm Retrospective Cohort Study in GnRH Antagonist IVF Cycles","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHormonal contraceptives have a broad range of indications beyond pregnancy prevention in the field of gynecology. Their use as pretreatment prior to assisted reproductive technologies (ART), particularly in controlled ovarian stimulation (COS), includes menstrual cycle scheduling, synchronization of the oocyte cohort, modulation of the endocrine environment prior to stimulation, and prevention of functional ovarian cyst formation [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe suppressive effects of hormonal contraceptives on follicle-stimulating hormone (FSH) and luteinizing hormone (LH) may facilitate better synchronization of follicular development during COS. Combined oral contraceptive pills (COCPs), which include both estrogen and progestin, strongly suppress the hypothalamic\u0026ndash;pituitary\u0026ndash;ovarian (HPO) axis. However, concerns have been raised regarding their potential negative impact on follicular growth and endometrial receptivity. In contrast, progestin-only agents (e.g., norethisterone) may suppress GnRH pulsatility with relatively less interference in endogenous hormonal dynamics [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA prospective randomized trial investigating hormonal pretreatment prior to in vitro fertilization (IVF) found that women who received hormonal contraceptives required higher total gonadotropin doses, but this did not adversely affect the number of oocytes retrieved or pregnancy outcomes [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Furthermore, a meta-analysis of four randomized controlled trials (RCTs) concluded that, in GnRH antagonist cycles, women with and without prior hormonal contraceptive pretreatment had comparable ongoing pregnancy rates and oocyte retrieval outcomes [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThus, the effectiveness of pretreatment prior to COS initiation remains unclear. In particular, few studies have comprehensively compared the effects of COCPs, progestin-only agents, and no pretreatment on hormonal profiles, follicular dynamics, and clinical outcomes\u0026mdash;including cumulative pregnancy and live birth rates\u0026mdash;in women with normal ovarian response.\u003c/p\u003e \u003cp\u003eTherefore, the objective of this study was to investigate whether hormonal pretreatment strategies\u0026mdash;including progestin-only agents and combined oral contraceptive pills\u0026mdash;have an impact on ART outcomes, by comparing hormone profiles, follicular development, and cumulative reproductive results in GnRH antagonist IVF/ICSI cycles.\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cp\u003eThis retrospective cohort study was conducted at Kobanawa Clinic and included 240 ART cycles performed between April 2022 and December 2024. A total of 363 cases were initially screened, and 240 cycles meeting the eligibility criteria were included after applying exclusion criteria. After approval by the Medical Corporation Kobanawa Clinic Ethic Screening Committee, this study was conducted with opt-out disclosure of information.\u003c/p\u003e\n\u003cp\u003eBased on previous studies reporting cumulative live birth rates (CLBR) ranging from 76% to 86%[5], sample size calculation was performed using Cohen\u0026rsquo;s \u003cem\u003ew\u003c/em\u003e for chi-square testing among three independent groups. The resulting effect size was estimated as\u0026nbsp;\u003cem\u003ew\u003c/em\u003e \u0026asymp; 0.26 (small to medium).[6]\u003cbr\u003e\u0026nbsp;Using G*Power version X.X (Heinrich Heine University, D\u0026uuml;sseldorf, Germany), with a two-sided significance level of 0.05 and 80% power, the minimum required sample size was calculated to be 108 participants (36 per group).[7]\u003c/p\u003e\n\u003cp\u003eThis study included the first ART cycle of each patient who underwent controlled ovarian stimulation (COS) using recombinant FSH (rFSH) monotherapy with either follitropin alfa, beta, or delta. All patients were covered under the Japanese Healthcare Insurance System and were aged \u0026le;42 years.\u003c/p\u003e\n\u003cp\u003eExclusion criteria included patients who deviated from the prescription guidelines for Follitropin Alfa, Beta and Delta, those who received concurrent concomitant treatment with human menopausal gonadotropin (HMG), urinary FSH (uFSH), clomiphene, or letrozole, and those who had anti-M\u0026uuml;llerian hormone (AMH) levels \u0026lt; 1.2 ng/mL, classified as low prognosis (Figure1). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAmong 363 patients assessed for eligibility, 123 were excluded due to (1) concurrent use of HMG, urinary FSH, clomiphene, or letrozole, or (2) low ovarian reserve, defined as AMH \u0026lt; 1.2 ng/mL.\u003c/p\u003e\n\u003cp\u003eA total of 240 patients were included in the final analysis.\u003c/p\u003e\n\u003cp\u003eThey were categorized into three groups based on pretreatment:\u003c/p\u003e\n\u003cp\u003eCOCP pretreatment (n = 50), progestin-only pretreatment (P group, n = 77), and no pretreatment (control group, n = 113).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis retrospective study included patients who underwent controlled ovarian stimulation (COS) with or without pretreatment using combined oral contraceptive pills (COCP) or progestin-only pretreatment (P). In the COCP and P groups, pretreatment medications were administered for a variable number of days. The duration was determined based on patient preference and clinic scheduling needs\u003cbr\u003e\u0026nbsp;The choice of pretreatment was not randomized, but rather based on clinical discretion and patient preference as part of routine care.\u003c/p\u003e\n\u003cp\u003eIn COS, daily subcutaneous injections of Follitropin Alfa (Gonal F; Merck BioPharma, Tokyo, Japan) or Follitropin Beta (Foristim, Organon, Osaka, Japan) or Follitropin Delta (Rekovelle; Ferring Pharma, Tokyo) as a mono protocol with rFSH were administered starting on days 1-3 of menstruation, using the COS with GnRH antagonist protocol.\u003c/p\u003e\n\u003cp\u003eThe starting dose of follitropin alfa and beta was determined using the gonadotropin starting dose calculator developed by Kobanawa with a fixed dose. [8]\u003c/p\u003e\n\u003cp\u003eThe daily individualized dose of follitropin delta was determined using the serum anti-M\u0026uuml;llerian hormone (AMH) level within the previous 12 months and body weight, with a fixed dose used throughout the stimulation.[9]\u003c/p\u003e\n\u003cp\u003eGonadotropin-releasing hormone antagonists (Ganirest; MSD, Tokyo, Japan) were started at a dose of 0.25 mg/day when the primary follicle reached approximately 14 mm. When several leading follicles reached 17\u0026ndash;20 mm, gonadotropins and GnRH antagonist doses of 0.25 mg/day were terminated, and on the same day or the next day, 250 \u0026mu;g of choriogonadotropin alfa was administered.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOocyte retrieval was performed 36-39 hours after triggering.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAfter oocyte retrieval, insemination and intracytoplasmic sperm injection (ICSI) were performed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThen, fertilized oocytes were cultured to blastocysts, which were then frozen. Thawed embryos were transferred during the next menstrual cycle or later by hormone replacement cycles (HRCs) or natural cycles (NCs). In HRC, hormone replacement of estrogen (Estrana Tapes, Hisamitsu Pharmaceutical, Tokyo) at 0.72 mg \u0026times;4 every other day was started on days 1-3 of menstruation. With endometrial thickening confirmed to be at least 7 mm, progesterone (UTROGESTAN; Fuji Pharma Co.,Ltd., Tokyo) 200 mg \u0026times;3/day was commenced, and blastocyst transfer was performed six days later (P+5). We performed a single embryo transfer (SET). In the NC group, blastocysts were transferred on the fifth day after natural ovulation without the use of drugs.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eClinical pregnancy was defined as a case in which the fetal sac was confirmed by transvaginal ultrasonography within four to five weeks of gestation determined from the day of embryo transfer. After pregnancy, birth outcomes were tracked based on reports from the patients or the hospitals where the delivery occurred\u003c/p\u003e\n\u003cp\u003eBlood samples were collected during the study to assess AMH, FSH, luteinizing hormone (LH), estradiol, and progesterone levels. AMH concentrations were measured during screening before the start of the cycle and used to determine the starting dose of gonadotropins. AMH levels were measured using an automated Elecsys AMH assay (Roche Diagnostics, Basel, Switzerland). Serum samples were used to assess endocrine parameters (FSH, LH, estradiol, and progesterone).\u003c/p\u003e\n\u003cp\u003eMature oocytes (MII) were defined as oocytes confirmed by denudation for intracytoplasmic sperm injection (ICSI) or oocytes confirmed zygotes with two pronuclei by insemination (conventional IVF).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe fertilization rate was defined as the number of pronuclei confirmed per insemination by IVF or ICSI punctures. The embryo culture results were compared based on blastocyst rates, defined as the number of high-quality blastocysts (Gardner\u0026rsquo;s classification\u0026nbsp;of 3BB or higher) per cultured embryo.[10]\u003c/p\u003e\n\u003cp\u003eClinical pregnancy was defined as a case in which the fetal sac was confirmed by transvaginal ultrasonography within four to five weeks of gestation determined from the day of embryo transfer. After pregnancy, birth outcomes were tracked based on reports from the patients or the hospitals where the delivery occurred\u003c/p\u003e\n\u003cp\u003eCumulative pregnancy and live birth rates were calculated as the probability\u0026nbsp;of a single-cycle embryo leading to pregnancy or live birth over multiple transfers.[11]\u003c/p\u003e\n\u003cp\u003eThe primary outcome of this study was the cumulative live birth rate (CLBR) per cycle according to each pretreatment strategy.\u003c/p\u003e\n\u003cp\u003eFor baseline patient characteristics, numerical variables were compared among the three groups using one-way analysis of variance (ANOVA), while categorical variables were compared using the chi-square test.\u003c/p\u003e\n\u003cp\u003eTo assess clinical outcomes, multivariable analyses were conducted to adjust for potential confounders identified as significantly different among the groups at baseline. Specifically, multiple linear regression and logistic regression analyses were performed, incorporating these covariates to compare the three groups.\u003c/p\u003e\n\u003cp\u003eTo evaluate the variability in follicular size synchronization, Levene\u0026rsquo;s test was used to compare the homogeneity of variance among groups.\u003c/p\u003e\n\u003cp\u003eAll statistical analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). EZR is a modified version of the R Commander designed to provide additional statistical functions frequently used in biostatistics.[12]\u003c/p\u003e\n\u003cp\u003e\u003cqb-toolbar contenteditable=\"false\" id=\"qb-toolbar-container\" style=\"display: none;\"\u003e\u003cqb-div class=\"qb-toolbar__wrapper qb-toolbar__wrapper--hide\"\u003e\u003c/qb-div\u003e\u003c/qb-toolbar\u003e\u003c/p\u003e\n\u003cdiv style=\"all: initial !important;\"\u003e\u003cbr\u003e\u003c/div\u003e\n\u003cp\u003e\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eBaseline characteristics were compared among the three groups: COCP, Control, and Progesterone (P) (Table.1).\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" align=\"\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eVariable\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003eCOCP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003en\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e113\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eDuration of medication (days)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e13.52 (3.25)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e0 (0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e9.87 (0.75)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eAge, years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e32.82 (3.90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e34.39 (3.68)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e32.79 (3.90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.006\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eAMH, ng/ml\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e4.45 (3.06)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e4.17 (2.70)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e4.37 (2.80)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.814\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eAFC, follicles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e15.56 (6.43)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e16.41 (6.38)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e17.17 (7.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.407\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eBasal E2, pg/ml\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e35.53 (21.36)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e67.65 (392.89)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e25.34 (16.09)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.538\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eBasal FSH, IU/L\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e7.60 (2.17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e6.97 (1.61)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e6.68 (1.70)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.017\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eBasal LH, IU/L\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e7.88 (3.40)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e6.02 (2.22)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e6.37 (3.03)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eBody weight, kg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e64.97 (53.53)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e57.62 (10.99)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e58.89 (11.99)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.253\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eGonadotropin.preparation: Follitropin alfa, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e27 (54.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e58 (51.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e43 (55.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.97\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eGonadotropin.preparation: Follitropin beta, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e2 (4.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e6 (5.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e3 (3.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eGonadotropin.preparation: Follitropin delta, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e21 (42.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e49 (43.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e31 (40.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eTrigger.methods: GnRH, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e47 (94.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e94 (83.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e65 (84.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.172\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eTrigger.methods: hCG, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e3 (6.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e19 (16.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e12 (15.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eFertilization.methods: c-IVF, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e44 (88.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e78 (69.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e65 (84.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.007\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 232px;\"\u003e\n \u003cp\u003eFertilization.methods: ICSI, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e6 (12.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e35 (31.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e12 (15.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eTable.1 Baseline characteristics and treatment parameters of the three groups.\u003c/p\u003e\n\u003cp\u003eNumerical variables are presented as mean (standard deviation), and categorical variables as number (percentage). Statistical comparisons among the COCP, Control, and Progesterone groups were performed using one-way ANOVA for numerical variables and chi-square tests for categorical variables. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThere were significant differences in patient age (\u003cem\u003ep\u003c/em\u003e = 0.006), basal FSH (\u003cem\u003ep\u003c/em\u003e = 0.017), and basal LH levels (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001) among the groups. The duration of medication also varied significantly, with the COCP group having the longest mean duration (13.52 \u0026plusmn; 3.25 days) and the Control group having none due to lack of pretreatment (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001). However, there was no significant difference in duration between the COCP and P groups, suggesting comparable exposure to pretreatment medications within those two groups.\u003c/p\u003e\n\u003cp\u003eThe proportion of fertilization methods differed significantly among groups (\u003cem\u003ep\u003c/em\u003e = 0.007), with the COCP and Progesterone groups showing a higher rate of conventional IVF compared to the Control group. Other variables, including AMH, AFC, basal estradiol, body weight, gonadotropin preparation type, and trigger method, did not show statistically significant differences between groups (Table.1).\u003c/p\u003e\n\u003cp\u003eBased on these results, age, basal FSH, basal LH, and fertilization method were considered potential confounding factors and were included as covariates in subsequent multivariable analyses.\u003c/p\u003e\n\u003cp\u003eCompared to the COCP and control groups, the P group demonstrated significantly higher values in several key embryological outcomes. Specifically, the oocyte maturation rate (\u003cem\u003ep\u003c/em\u003e = 0.040), fertilization rate (\u003cem\u003ep\u003c/em\u003e = 0.038), and the number of good-quality blastocysts (\u003cem\u003ep\u003c/em\u003e = 0.015) were all significantly greater in the P group after adjustment for confounding factors. In addition, the blastocyst development rate was also significantly improved (\u003cem\u003ep\u003c/em\u003e = 0.029) (Table.2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable.2 Comparison of ovarian stimulation characteristics, embryological outcomes, and clinical outcomes among the COCP, Control, and P groups.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eVariable\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003eCOCP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003eControl\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003eUnivariate\u0026nbsp;P-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003eMultivariate\u0026nbsp;P-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eStimulation days, days\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e13.54 (2.13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e13.49 (3.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e14.39 (2.97)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.079\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.078\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eMaximum follicle diameter on days 6\u0026ndash;8 of stimulation, mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e16.7 (3.77)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e16.05 (3.09)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e16.39 (3.55)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.513\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eminimum follicle diameter on days 6\u0026ndash;8 of stimulation, mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e9.12 (1.76)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e9.57 (2.08)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e9.22 (2.67)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.398\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.256\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eFollicle count \u0026ge;14 mm on the day of trigger, folllicles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e16.96 (6.04)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e17 (6.51)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e17.47 (7.52)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.876\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.780\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eFollicle count \u0026ge;16 mm on the day of trigger, folllicles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e14.3 (5.23)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e15.15 (6.08)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e15.03 (7.18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.359\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eFollicle count \u0026ge;18 mm on the day of trigger, folllicles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e10.44 (4.57)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e11.26 (5.25)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e12.34 (5.87)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.132\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.197\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eFollicle count \u0026ge;20 mm on the day of trigger, folllicles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e6.24 (4.19)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e6.45 (4.78)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e6.58 (4.93)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.922\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.899\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eTotal gonadotropin dosage, mcg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e141.86 (57.35)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e148.89 (74.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e135.55 (51.57)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.890\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eE2 level on the day of trigger, pg/ml\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e3880.98 (1615.67)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e3889.8 (2076.56)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e3994.14 (2606.07)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.939\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.853\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eP4 level on the day of trigger, ng/ml\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e1.67 (2.38)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e1.43 (0.82)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e1.28 (0.93)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.278\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.342\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eNumber of oocytes retrieved, oocytes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e14.94 (6.02)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e16.03 (6.66)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e16.43 (7.21)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.466\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.736\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eFollicular Output Rate (FORT), No. follicles≧16mm /AFC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e1.00 (0.42)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e0.98 (0.38)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e0.96 (0.50)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.712\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eFollicle-to-Oocyte Index (FOI), No.oocytes/ AFC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e0.98 (0.14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e0.97 (0.12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e0.95 (0.12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.487\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.470\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eOvarian Sensitivity Index (OSI), oocytes/mcg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e0.12 (0.06)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e0.14 (0.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e0.15 (0.14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.301\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.453\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eNumber of mature oocytes, oocytes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e14.56 (6.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e15.36 (6.71)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e16.16 (7.20)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.421\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.803\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eOocyte maturation rate, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e97.00 (6.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e95.00 (8.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e98.00 (5.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.022\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eNumber of two-pronuclei (2PN) zygotes, zygotes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e8.38 (4.15)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e10.05 (5.43)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e10.66 (5.07)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.044\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.160\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eFertilization rate, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e58.00 (20.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e66.00 (21.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e67.00 (15.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.028\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.038\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eNumber of good-quality blastocysts, \u0026nbsp;blastocysts\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e4.92 (3.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e6.00 (4.02)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e7.23 (4.22)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eBlastocyst development rate, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e57.00 (22.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e59.00 (22.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e66.00 (21.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.039\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.029\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eNumber of embryo transfers, transfers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e1.84 (1.28)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e1.57 (0.99)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e1.51 (0.88)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.177\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.202\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eCumulative pregnancy rate, % (n)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e86 (43)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e85 (96)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e97.4(75)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.090\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 210px;\"\u003e\n \u003cp\u003eCumulative live birth rate, % (n)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 70px;\"\u003e\n \u003cp\u003e72 (36)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e75.2 (85)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 82px;\"\u003e\n \u003cp\u003e87 (67)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 61px;\"\u003e\n \u003cp\u003e0.0726\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.237\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eData are presented as mean (standard deviation) for continuous variables or number (percentage) for categorical variables. Univariate \u003cem\u003ep\u003c/em\u003e-values were calculated using one-way ANOVA or chi-square tests, as appropriate. For multivariable analysis, age, basal FSH, and basal LH were included as covariates for outcomes up to oocyte retrieval. For outcomes following fertilization, fertilization methods was additionally included as a confounding factor.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFurthermore, although not reaching statistical significance in the multivariable analysis, the P group showed a trend toward a higher cumulative live birth rate (87.0%) compared with the COCP (72.0%) and control groups (75.2%) (\u003cem\u003ep\u003c/em\u003e = 0.237), as well as a higher cumulative pregnancy rate (\u003cem\u003ep\u003c/em\u003e = 0.090) (Table.2).\u003c/p\u003e\n\u003cp\u003eIn addition, the effect of pretreatment on follicular synchronization was evaluated by comparing follicular size distribution among the three groups.\u003c/p\u003e\n\u003cp\u003eTo assess the consistency of follicular synchronization patterns across different pretreatment groups, we evaluated the within-group variability of the proportions of follicles \u0026ge;20mm, \u0026ge;18mm, and \u0026ge;16mm relative to follicles \u0026ge;14mm.\u003c/p\u003e\n\u003cp\u003eThree indices of dispersion were calculated within each group: standard deviation (SD), variance (Var), and interquartile range (IQR). Among the three groups\u0026mdash;P group (progestin-only pretreatment), COCP group (combined oral contraceptive pills), and control group (no pretreatment)\u0026mdash;the P group consistently showed the smallest values for all three dispersion measures (Table.3).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable.3 Within-group variability in follicle size ratios (\u0026ge;20mm, \u0026ge;18mm, \u0026ge;16mm per \u0026ge;14mm) across pretreatment groups.\u003c/p\u003e\n\u003ctable border=\"0\" cellpadding=\"0\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003ePretreatment Group\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eSD (20mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eVar (20mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eIQR (20mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eSD (18mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eVar (18mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eIQR (18mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eSD (16mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eVar (16mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eIQR (16mm/14mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eP\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.230\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.053\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.310\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.219\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.048\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.019\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.231\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eCOCP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.249\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.062\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.335\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.254\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.064\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.326\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.145\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.021\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.246\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.239\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.057\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.338\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.193\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.037\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.255\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.200\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eStandard deviation (SD), variance (Var), and interquartile range (IQR) were calculated for each group: P group (progestin-only pretreatment), COCP group (combined oral contraceptive pills), and Control group (no pretreatment). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo formally assess whether the P group had significantly lower variability compared to the COCP and control groups, levene\u0026rsquo;s test was used to compare intra-group variability in follicle size synchronization, as measured by the ratios of follicles \u0026ge;20 mm, \u0026ge;18 mm, and \u0026ge;16 mm to those \u0026ge;14 mm. The analysis revealed that only the 18mm/14mm ratio showed a statistically significant difference in variance across pretreatment groups (p = 0.0001), while the 20mm/14mm and 16mm/14mm ratios did not (p = 0.4809 and p = 0.3710, respectively) (Table 4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable.4 Results of Levene\u0026rsquo;s tests comparing variance in follicle size synchronization ratios among the three pretreatment groups\u003c/p\u003e\n\u003ctable border=\"0\" cellpadding=\"0\" class=\"fr-table-selection-hover\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 23.0139%;\"\u003e\n \u003cp\u003eRatio Type\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 48.8029%;\"\u003e\n \u003cp\u003eOverall Levene Test p-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 23.0139%;\"\u003e\n \u003cp\u003e20mm / 14mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 46.5037%;\"\u003e\n \u003cp\u003e0.4809\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 23.0139%;\"\u003e\n \u003cp\u003e18mm / 14mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 46.5037%;\"\u003e\n \u003cp\u003e0.0001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 23.0139%;\"\u003e\n \u003cp\u003e16mm / 14mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 46.5037%;\"\u003e\n \u003cp\u003e0.3710\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eComparison\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.7388%;\"\u003e\n \u003cp\u003eLevene Statistic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.3217%;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eControl vs P\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.7388%;\"\u003e\n \u003cp\u003e5.353\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.3217%;\"\u003e\n \u003cp\u003e0.0218\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eControl vs COCP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.7388%;\"\u003e\n \u003cp\u003e6.606\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.3217%;\"\u003e\n \u003cp\u003e0.0111\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eP vs COCP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.7388%;\"\u003e\n \u003cp\u003e18.947\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.3217%;\"\u003e\n \u003cp\u003e\u0026lt;0.0001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eTo further explore this difference, post hoc pairwise Levene\u0026rsquo;s tests were performed for the 18mm/14mm ratio. The P group showed significantly lower variance than both the Control (p = 0.0218) and COCP groups (p \u0026lt; 0.0001), while the Control group also had significantly lower variance than the COCP group (p = 0.0111) (Table 4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo visually assess differences in follicle synchronization, the 18mm/14mm ratio was plotted by group using boxplots (Figure.2).\u003c/p\u003e\n\u003cp\u003eBoxplots demonstrate inter-group differences in variability. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe P group demonstrated the least variability, as shown by the tight distribution and narrow interquartile range. In contrast, the COCP group exhibited the greatest variability, with a broader range and higher dispersion of individual values. These visual findings align with the statistical results from Levene\u0026rsquo;s test (p = 0.0001), further supported by post hoc analyses showing significant variance differences between all group pairs.\u003c/p\u003e\n\u003cp\u003eLogistic regression analysis was performed to identify factors associated with achieving a ratio of \u0026ge;60% for follicles \u0026ge;18 mm relative to those \u0026ge;14 mm (18/14 ratio). The independent variables included pretreatment group (P vs COCP, P vs control), basal FSH, basal LH, age, and gonadotropin type. The analysis revealed that the P group was significantly associated with a higher probability of achieving an 18/14 ratio \u0026ge;60%, compared to the COCP group (OR: 2.34, 95% CI: 1.04\u0026ndash;5.28, P = 0.040). No significant difference was observed between the P group and the control group (OR: 1.22, 95% CI: 0.59\u0026ndash;2.52, P = 0.59). (Figure.3)\u003c/p\u003e\n\u003cp\u003eThe analysis included pretreatment group (P vs COCP, P vs control), age, basal FSH, basal LH, and gonadotropin type.\u0026nbsp;\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we evaluated the impact of different pretreatment strategies\u0026mdash;P group, COCP group, and control group\u0026mdash;on IVF/ICSI outcomes using a GnRH antagonist protocol. The results revealed that the P group showed a trend toward higher cumulative pregnancy and live birth rates compared with the other groups, along with significantly improved follicular synchronization. When using the ratio of follicles \u0026ge;18 mm to those \u0026ge;14 mm (18/14 ratio) as a proxy for synchrony, the P group exhibited the highest values and the lowest intra-group variability, suggesting a more uniform follicular cohort.\u003c/p\u003e\n\u003cp\u003eAdditionally, the P group demonstrated significantly higher numbers of good-quality blastocysts and higher blastocyst development rates, indicating improved embryo developmental efficiency. These findings may be explained by the influence of progestin on endogenous hormonal dynamics. Progestin pretreatment has been shown to suppress GnRH pulsatility, thereby reducing FSH and LH secretion [13\u0026ndash;15]. It also limits early follicular sensitivity to FSH, preventing premature recruitment and contributing to synchronized follicular development [16,17].\u003c/p\u003e\n\u003cp\u003eMechanistically, these effects may be mediated via progesterone\u0026rsquo;s action on hypothalamic kisspeptin neurons. Kisspeptin is a potent activator of the hypothalamic\u0026ndash;pituitary\u0026ndash;gonadal axis, stimulating GnRH secretion and, in turn, FSH and LH release [18\u0026ndash;20]. Nearly all arcuate nucleus (ARC) kisspeptin neurons express progesterone receptors, and the surge in progesterone levels following ovulation suppresses LH secretion via these pathways [21,22]. Furthermore, kisspeptin has been shown to inhibit the upregulation of FSH receptor (FSHR) expression in granulosa cells [23].\u003c/p\u003e\n\u003cp\u003eThus, while LH surges are effectively prevented, FSH is not excessively suppressed; instead, follicular sensitivity to FSH is attenuated, suppressing early follicular recruitment prior to menses. This mechanism likely contributes to more synchronized follicle development at the onset of COS.\u003c/p\u003e\n\u003cp\u003eIn contrast, COCPs contain ethinyl estradiol (EE), which acts to suppress endogenous gonadotropin release [24\u0026ndash;26] and upregulate progesterone receptor expression, thereby potentiating progestin effects [27]. However, excessive suppression of endogenous gonadotropins with COCPs may delay stimulation onset, blunt E2 rise, and increase the duration and total dose of gonadotropins required [3].\u003c/p\u003e\n\u003cp\u003eBoth P and COCP pretreatment may reduce the risk of functional ovarian cyst formation, a frequent issue in reproductive-aged women. In large cross-sectional studies, ovarian cysts larger than 30 mm were found in 4\u0026ndash;7% of women undergoing baseline ultrasonography before hormonal contraception initiation [28]. These cysts have been associated with poor ovarian response in IVF cycles, particularly when measuring 30\u0026ndash;60 mm [29\u0026ndash;31]. Several studies have reported that pretreatment with oral contraceptives reduces the incidence of functional ovarian cysts [32], and this effect is particularly evident with progestins [33]. Therefore, prevention of cyst formation may be another contributing factor to improved follicular synchronization at the start of COS.\u003c/p\u003e\n\u003cp\u003eWhile some retrospective studies have associated hormonal contraceptive pretreatment with reduced live birth rates after fresh transfer (42.6% vs. 52.8%, P\u0026lt;.001) and lower cumulative live birth rates (62.8% vs. 67.6%, P=.01) [34], a 2017 Cochrane review of 29 RCTs in GnRH agonist and antagonist cycles found that pretreatment with hormonal contraception may reduce the risk of pregnancy loss [33]. However, other RCTs have shown no significant effect on clinical pregnancy or cumulative live birth rates when hormonal contraception was administered for 12\u0026ndash;30 days with a 5-day washout period [35].\u003c/p\u003e\n\u003cp\u003eIn our study, the P group showed significantly higher fertilization rates and blastocyst formation rates, which translated into an increased number of viable embryos per cycle. This enhanced oocyte-to-blastocyst efficiency likely contributed to the trend toward higher cumulative pregnancy and live birth rates in the P group. These results highlight the importance of optimizing follicular dynamics to improve embryological outcomes and overall ART success.\u003c/p\u003e\n\u003cp\u003eThe superiority of the P group may also be linked to baseline LH levels. Persistently elevated LH during the follicular phase can trigger premature meiotic resumption, oocyte nuclear damage, and apoptosis [37,38]. High LH also promotes excess androgen production by stimulating theca cells, leading to hyperandrogenism [39]. Elevated androgen concentrations in follicular fluid can disrupt intracellular calcium oscillations in oocytes, impeding cytoplasmic maturation and meiotic competence [40]. Oocytes retrieved under high LH conditions may exhibit excessive fragmentation and asymmetric cleavage, with negative implications for fertilization and embryo development [41].\u003c/p\u003e\n\u003cp\u003eIn our study, the COCP group had significantly higher basal LH levels than the control and P groups. This may reflect the lower doses of progestin in COCP formulations (e.g., norgestrel 0.5 mg or levonorgestrel 0.09 mg), compared to the higher-dose norethisterone (5 mg) used in the P group [42]. Therefore, the P group may have benefited from stronger suppression of LH and androgens, resulting in the retrieval of higher-quality oocytes and better embryo development.\u003c/p\u003e\n\u003cp\u003eTaken together, our findings suggest that progestin-only pretreatment leads to superior follicular synchronization, lower LH exposure, and improved embryo developmental potential. These advantages may ultimately enhance ART efficiency, particularly by increasing the number of transferable embryos and improving the likelihood of achieving pregnancy and live birth per cycle.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eAFC: Antral Follicle Count\u003c/p\u003e\n\u003cp\u003eAMH: Anti-M\u0026uuml;llerian Hormone\u003c/p\u003e\n\u003cp\u003eANOVA: Analysis of Variance\u003c/p\u003e\n\u003cp\u003eARC: Arcuate Nucleus\u003c/p\u003e\n\u003cp\u003eART: Assisted Reproductive Technology\u003c/p\u003e\n\u003cp\u003eCLBR: Cumulative Live Birth Rate\u003c/p\u003e\n\u003cp\u003eCOCP: Combined Oral Contraceptive Pills\u003c/p\u003e\n\u003cp\u003eCOS: Controlled Ovarian Stimulation\u003c/p\u003e\n\u003cp\u003eE2: Estradiol\u003c/p\u003e\n\u003cp\u003eEE: Ethinyl Estradiol\u003c/p\u003e\n\u003cp\u003eET: Embryo Transfer\u003c/p\u003e\n\u003cp\u003eFSH: Follicle-Stimulating Hormone\u003c/p\u003e\n\u003cp\u003eFSHR: Follicle-Stimulating Hormone Receptor\u003c/p\u003e\n\u003cp\u003eGnRH: Gonadotropin-Releasing Hormone\u003c/p\u003e\n\u003cp\u003eHMG: Human Menopausal Gonadotropin\u003c/p\u003e\n\u003cp\u003eHPO: Hypothalamic\u0026ndash;Pituitary\u0026ndash;Ovarian\u003c/p\u003e\n\u003cp\u003eHRC: Hormone Replacement Cycle\u003c/p\u003e\n\u003cp\u003eICSI: Intracytoplasmic Sperm Injection\u003c/p\u003e\n\u003cp\u003eIQR: Interquartile Range\u003c/p\u003e\n\u003cp\u003eIVF: In Vitro Fertilization\u003c/p\u003e\n\u003cp\u003eLH: Luteinizing Hormone\u003c/p\u003e\n\u003cp\u003eMII: Metaphase II Oocyte\u003c/p\u003e\n\u003cp\u003eNC: Natural Cycle\u003c/p\u003e\n\u003cp\u003eOR: Odds Ratio\u003c/p\u003e\n\u003cp\u003eRCT: Randomized Controlled Trial\u003c/p\u003e\n\u003cp\u003eSD: Standard Deviation\u003c/p\u003e\n\u003cp\u003eSET: Single Embryo Transfer\u003c/p\u003e\n\u003cp\u003erFSH: Recombinant Follicle-Stimulating Hormone\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eOur study was approved by the Medical Corporation Kobanawa Clinic Ethic Screening Committee (202311164) and in accordance with the Helsinki declaration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors received no specific funding for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMasato Kobanawa: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing\u0026ndash;original draft, and Writing\u0026ndash;review \u0026amp; editing\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets supporting the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe express special gratitude to\u0026nbsp;Editage (www.editage.com) for English language editing.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eACOG Practice Bulletin No. 110: noncontraceptive uses of hormonal contraceptives. Obstet Gynecol 2010;115:206\u0026ndash;18.\u003c/li\u003e\n\u003cli\u003eD\u0026apos;Arpe S, Di Feliciantonio M, Candelieri M, Franceschetti S, Piccioni MG, Bastianelli C. Ovarian function during hormonal contraception assessed by endocrine and sonographic markers: a systematic review. Reprod Biomed Online. 2016;33(4):436-448.\u003c/li\u003e\n\u003cli\u003eC\u0026eacute;drin-Durnerin I, Bst\u0026auml;ndig B, Parneix I, Bied-Damon V, Avril C, Decanter C, et al. Effects of oral contraceptive, synthetic progestogen or natural estrogen pre-treatments on the hormonal profile and the antral follicle cohort before GnRH antagonist protocol. Hum Reprod 2007;22:109\u0026ndash;16.\u003c/li\u003e\n\u003cli\u003eGriesinger G, Venetis CA, Marx T, Diedrich K, Tarlatzis BC, Kolibianakis EM. Oral contraceptive pill pretreatment in ovarian stimulation with GnRH antagonists for IVF: a systematic review and meta-analysis. Fertil Steril 2008;90: 1055\u0026ndash;63.\u003c/li\u003e\n\u003cli\u003eKobanawa M, Iwami N, Hanaoka M, Enatsu K, Ichiyama T. Cost-Effectiveness and Clinical Outcomes of Controlled Ovarian Stimulation With Follitropin Delta and Follitropin Alfa: A Retrospective Study. Cureus. 2024;16(12):e76371.\u003c/li\u003e\n\u003cli\u003eCohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum Associates\u003c/li\u003e\n\u003cli\u003eKang H. Sample size determination and power analysis using the G*Power software. J Educ Eval Health Prof. 2021;18:17.\u003c/li\u003e\n\u003cli\u003eKobanawa M. The gonadotropins starting dose calculator, which can be adjusted the target number of oocytes and stimulation duration days to achieve individualized controlled ovarian stimulation in Japanese patients. Reprod Med Biol. 2023;22(1):e12499.\u003c/li\u003e\n\u003cli\u003eIliodromiti S, Salje B, Dewailly D, et al.: Non-equivalence of anti-M\u0026uuml;llerian hormone automated assays-clinical implications for use as a companion diagnostic for individualised gonadotrophin dosing. Hum Reprod. 2017;32:1710-5. \u003c/li\u003e\n\u003cli\u003eGardner DK, Schoolcraft WB: Culture and transfer of human blastocysts. Curr Opin Obstet Gynecol. 1999;11:307-11. \u003c/li\u003e\n\u003cli\u003eMaheshwari A, McLernon D, Bhattacharya S: Cumulative live birth rate: time for a consensus?. Hum Reprod. 2015;30:2703-7.\u003c/li\u003e\n\u003cli\u003eKanda Y. Investigation of the freely available easy-to-use software \u0026lsquo;EZR\u0026rsquo; for medical statistics. Bone Marrow Transplant. 2013; 48(3): 452\u0026ndash;458.\u003c/li\u003e\n\u003cli\u003eLesoon LA, Mahesh VB. Stimulatory and inhibitory effects of progesterone on FSH secretion by the anterior pituitary. J Steroid Biochem Mol Biol. 1992;42(5):479-491.\u003c/li\u003e\n\u003cli\u003eRichter TA, Robinson JE, Evans NP. Progesterone blocks the estradiol-stimulated luteinizing hormone surge by disrupting activation in response to a stimulatory estradiol signal in the ewe. Biol Reprod. 2002;67(1):119-125.\u003c/li\u003e\n\u003cli\u003eSkinner DC, Evans NP, Delaleu B, Goodman RL, Bouchard P, Caraty A. The negative feedback actions of progesterone on gonadotropin-releasing hormone secretion are transduced by the classical progesterone receptor. \u003cem\u003eProc Natl Acad Sci U S A\u003c/em\u003e. 1998;95(18):10978-10983.\u003c/li\u003e\n\u003cli\u003eObruca A, Korver T, Huber J, Killick SR, Landgren B, Struijs MJ. Ovarian function during and after treatment with the new progestagen Org 30659. Fertil Steril. 2001;76(1):108-115.\u003c/li\u003e\n\u003cli\u003eHeikinheimo O, Gordon K, Williams RF, Hodgen GD. Inhibition of ovulation by progestin analogs (agonists vs antagonists): preliminary evidence for different sites and mechanisms of actions. Contraception. 1995; 53:55\u0026ndash;64.\u003c/li\u003e\n\u003cli\u003ePinilla L, Aguilar E, Dieguez C, Millar RP, Tena-Sempere M. Kisspeptins and Reproduction: Physiological Roles and Regulatory Mechanisms. Physiol Rev (2012) 92(3):1235\u0026ndash;316. \u003c/li\u003e\n\u003cli\u003eMessager S, Chatzidaki EE, Ma D, Hendrick AG, Zahn D, Dixon J, et al. Kisspeptin Directly Stimulates Gonadotropin-Releasing Hormone Release via G Protein-Coupled Receptor 54. Proc Natl Acad Sci USA (2005) 102(5):1761\u0026ndash;6. \u003c/li\u003e\n\u003cli\u003eHrabovszky E. Neuroanatomy of the Human Hypothalamic Kisspeptin System. Neuroendocrinology (2014) 99(1):33\u0026ndash;48. \u003c/li\u003e\n\u003cli\u003eHe W, Li X, Adekunbi D, Liu Y, Long H, Wang L, et al. Hypothalamic Effects of Progesterone on Regulation of the Pulsatile and Surge Release of Luteinising Hormone in Female Rats. Sci Rep (2017) 7(1):8096. \u003c/li\u003e\n\u003cli\u003eClarkson J, d\u0026apos;Anglemont de Tassigny X, Moreno AS, Colledge WH, Herbison AE. Kisspeptin-GPR54 Signaling is Essential for Preovulatory Gonadotropin-Releasing Hormone Neuron Activation and the Luteinizing Hormone Surge. J Neurosci Off J Soc Neurosci (2008) 28(35):8691\u0026ndash;7. \u003c/li\u003e\n\u003cli\u003eFernandois D, Na E, Cuevas F, Cruz G, Lara HE, Paredes AH. Kisspeptin is involved in ovarian follicular development during aging in rats. J Endocrinol. 2016;228(3):161-170.\u003c/li\u003e\n\u003cli\u003eGoldzieher JW, Stanczyk FZ. Oral contraceptives and individual variability of circulating levels of ethinyl estradiol and progestins. Contraception. 2008;78(1):4-9.\u003c/li\u003e\n\u003cli\u003eZiegler D, Jaaskelainen AS, Brioschi PA, Fanchin R, Bulletti C. Synchronization of endogenous and exogenous FSH stimuli in controlled ovarian hyperstimulation (COH). Human Reproduction 1998;13(3):561‐4.\u003c/li\u003e\n\u003cli\u003eNestour E, Marraoui J, Lahlou N, Roger M, Ziegler D, Bouchard P. Role of estradiol in the rise in follicle‐stimulating hormone levels during the luteal‐follicular transition. Journal of Clinical Endocrinology and Metabolism 1993;77(2):439‐42.\u003c/li\u003e\n\u003cli\u003eWright AA, Fayad GN, Selgrade JF, Olufsen MS. Mechanistic model of hormonal contraception. PLoS Comput Biol. 2020;16(6):e1007848.\u003c/li\u003e\n\u003cli\u003eTeichmann AT, Brill K, Albring M, Schnitker J, Wojtynek P, Kustra E. The influence of the dose of ethinylestradiol in oral contraceptives on follicle growth. Gynecol Endocrinol 1995;9:299\u0026ndash;305.\u003c/li\u003e\n\u003cli\u003eThatcher SS, Jones E, DeCherney AH. Ovarian cysts decrease the success of controlled ovarian stimulation and in vitro fertilization. Fertil Steril 1989;52: 812\u0026ndash;6.\u003c/li\u003e\n\u003cli\u003eKeltz MD, Jones EE, Duleba AJ, Polcz T, Kennedy K, Olive DL. Baseline cyst formation after luteal phase gonadotropin-releasing hormone agonist administration is linked to poor in vitro fertilization outcome. Fertil Steril 1995;64:568\u0026ndash;72.\u003c/li\u003e\n\u003cli\u003eSegal S, Shifren JL, Isaacson KB, Leykin L, Chang Y, Pal L, et al. Effect of a baseline ovarian cyst on the outcome of in vitro fertilization-embryo transfer. Fertil Steril 1999;71:274\u0026ndash;7.\u003c/li\u003e\n\u003cli\u003eBiljan MM, Mahutte NG, Dean N, Hemmings R, Bissonnette F, Tan SL. Effects of pretreatment with an oral contraceptive on the time required to achieve pituitary suppression with gonadotropin-releasing hormone analogues and on subsequent implantation and pregnancy rates. Fertil Steril. 1998;70(6):1063-1069.\u003c/li\u003e\n\u003cli\u003eFarquhar C, Rombauts L, Kremer JA, Lethaby A, Ayeleke RO. Oral contraceptive pill, progestogen or oestrogen pretreatment for ovarian stimulation protocols for women undergoing assisted reproductive techniques. Cochrane Database Syst Rev 2017;5:CD006109.\u003c/li\u003e\n\u003cli\u003eLu Y, Wang Y, Zhang T, Wang G, He Y, Lindheim SR, et al. Effect of pretreatment oral contraceptives on fresh and cumulative live birth in vitro fertilization outcomes in ovulatory women. Fertil Steril 2020;114:779\u0026ndash;86.\u003c/li\u003e\n\u003cli\u003eMontoya-Botero P, Martinez F, Rodr\u0026iacute;guez-Purata J, Rodr\u0026iacute;guez I, Coroleu B, Polyzos NP. The effect of type of oral contraceptive pill and duration of use on fresh and cumulative live birth rates in IVF/ICSI cycles. Hum Reprod 2020; 35:826\u0026ndash;36.\u003c/li\u003e\n\u003cli\u003eHuirne JA, van Loenen AC, Donnez J, et al. Effect of an oral contraceptive pill on follicular development in IVF/ICSI patients receiving a GnRH antagonist: a randomized study. Reprod Biomed Online. 2006;13(2):235-245.\u003c/li\u003e\n\u003cli\u003eFranks S, Stark J, Hardy K. Follicle dynamics and anovulation in polycystic ovary syndrome. Hum Reprod Update 2008;14:367\u0026ndash;78. \u003c/li\u003e\n\u003cli\u003eFilicori M, Cognigni GE, Ciampaglia W. Effects of LH on oocyte yield and developmental competence. Hum Reprod 2003;18:1357\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eNelson VL, Qin KN, Rosenfield RL, et al. The biochemical basis for increased testosterone production in theca cells propagated from patients with polycystic ovary syndrome. J Clin Endocrinol Metab 2001;86:5925\u0026ndash;33. \u003c/li\u003e\n\u003cli\u003eTesarik J, Mendoza C. Direct non-genomic effects of follicular steroids on maturing human oocytes: oestrogen versus androgen antagonism. Hum Reprod Update 1997;3:95\u0026ndash;100.\u003c/li\u003e\n\u003cli\u003eStanger JD, Yovich JL. Reduced in-vitro fertilization of human oocytes from patients with raised basal luteinizing hormone levels during the follicular phase. Br J Obstet Gynaecol. 1985;92(4):385-393.\u003c/li\u003e\n\u003cli\u003eSchindler AE, Campagnoli C, Druckmann R, et al. Classification and pharmacology of progestins. Maturitas. 2003;46 Suppl 1:S7-S16.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"progestin-only pretreatment, combined oral contraceptive pills, follicular synchronization, in vitro fertilization, controlled ovarian stimulation, cumulative live birth rate","lastPublishedDoi":"10.21203/rs.3.rs-6998674/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6998674/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground:\u003c/h2\u003e \u003cp\u003eHormonal pretreatment prior to controlled ovarian stimulation (COS) in assisted reproductive technology (ART) is widely used to improve follicular synchronization and schedule flexibility. However, the comparative impact of different pretreatment strategies\u0026mdash;progestin-only, combined oral contraceptive pills (COCP), and no pretreatment\u0026mdash;on follicular dynamics and clinical outcomes remains unclear.\u003c/p\u003e\u003ch2\u003eMethods:\u003c/h2\u003e \u003cp\u003eIn this retrospective cohort study, 240 patients undergoing their first IVF/ICSI cycle with a GnRH antagonist protocol and recombinant FSH monotherapy were analyzed. Participants were divided into three groups: progestin-only pretreatment (P group), COCP pretreatment (COCP group), and no pretreatment (control group). Baseline characteristics, follicular development, embryo quality, and cumulative reproductive outcomes were compared. Levene\u0026rsquo;s test was used to assess follicular size variability, and multivariable regression analyses were performed to adjust for confounding variables.\u003c/p\u003e\u003ch2\u003eResults:\u003c/h2\u003e \u003cp\u003eThe P group demonstrated significantly improved follicular synchronization, as evidenced by the lowest variability in the ratio of follicles\u0026thinsp;\u0026ge;\u0026thinsp;18 mm to \u0026ge;\u0026thinsp;14 mm. Embryological outcomes were superior in the P group, with higher oocyte maturation rate (p\u0026thinsp;=\u0026thinsp;0.040), fertilization rate (p\u0026thinsp;=\u0026thinsp;0.038), and number of good-quality blastocysts (p\u0026thinsp;=\u0026thinsp;0.015) compared to the other groups. The blastocyst development rate was also significantly greater (p\u0026thinsp;=\u0026thinsp;0.029). Although cumulative live birth rate (CLBR) did not reach statistical significance, a trend toward higher CLBR was observed in the P group (87.0%) compared to COCP (72.0%) and control (75.2%).\u003c/p\u003e\u003ch2\u003eConclusion:\u003c/h2\u003e \u003cp\u003eProgestin-only pretreatment leads to superior follicular synchronization and improved embryo developmental potential in GnRH antagonist IVF/ICSI cycles. These benefits may enhance ART efficiency and contribute to improved cumulative outcomes.\u003c/p\u003e","manuscriptTitle":"Progestin-Only Pretreatment Enhances Follicular Synchronization and Embryo Development: A Three-Arm Retrospective Cohort Study in GnRH Antagonist IVF Cycles","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-04 05:31:45","doi":"10.21203/rs.3.rs-6998674/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"eeedf295-28fc-4e3e-bdf0-b7ce99c001f2","owner":[],"postedDate":"July 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-04T05:31:48+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-04 05:31:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6998674","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6998674","identity":"rs-6998674","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}