Impact of ovarian stimulation duration in GnRH antagonist protocols on the cumulative ongoing pregnancy rate in women with normal ovarian reserve: a cohort study.

Between January 2019 and December 2023, a total of 2,086 ovarian stimulation cycles using a GnRH antagonist protocol were evaluated in an intra-couple infertility context, excluding cycles involving preimplantation genetic testing or testicular sperm extraction. Among these, 376 cycles were excluded due to cycle dropout ( n  = 363), COS after ovarian tissue transplantation ( n  = 2), or oocyte cryopreservation following failure of sperm retrieval or sperm contamination ( n  = 11). Of the 1710 remaining cycles, an additional 254 were excluded based on extreme antral follicle count. Ultimately, 1456 cycles met all inclusion criteria and were analyzed in this study (Fig. 1 ). Of these, at least one embryo available for transfer was obtained in 1386 cycles (95.2%) with 964 (69.5%) resulting in a fresh embryo transfer. Fig. 1 Flowchart of the study population Flowchart of the study population For the calculation of the cumulative ongoing pregnancy rate, only cycles for which the reproductive potential of the stimulation cycle was fully exhausted were included. A cycle was considered evaluable when either an ongoing pregnancy had occurred or if all embryos originating from the cycle had been transferred. Based on this definition, 1339 cycles (92%) were eligible. This number corresponds to: cycles with an ongoing pregnancy after fresh or frozen embryo transfer ( n  = 487), cycles with no ongoing pregnancy but no remaining embryos to transfer (including cycles without any transferable embryo) ( N  = 782), and (3) cycles without any embryo ( N  = 70). cycles with an ongoing pregnancy after fresh or frozen embryo transfer ( n  = 487), cycles with no ongoing pregnancy but no remaining embryos to transfer (including cycles without any transferable embryo) ( N  = 782), and (3) cycles without any embryo ( N  = 70). The remaining 117 cycles (8%) were not included in the cumulative pregnancy rate analysis, as they had not yet resulted in pregnancy but still had at least one embryo available for potential future transfer. Patients’ characteristics as well as clinical, biological, and embryological parameters were analyzed across the three stimulation duration groups, defined by the 5th and 95th percentiles. Comparisons were performed between the short (≤ 8 days) and prolonged (≥ 14 days) groups versus the reference group (9–13 days) (Tables 1 , 2 and 3 ). A total of 122 cycles had a stimulation duration of ≤ 8 days, 1185 between 9 and 13 days (reference group) and 149 had a duration of ≥ 14 days. Median women age was significantly different between stimulation groups ( p  = 0.0004), being significantly higher in the prolonged stimulation group compared to the reference group. No significant difference was observed between the short and the reference groups. Ovarian reserve parameters (AMH level and AFC) also varied significantly, being higher in the short-duration group and lower in the prolonged group ( p  < 0.0001). No other significant differences were found in baseline characteristics or infertility etiology (Table 1 ). Pretreatment regimen varied significantly ( p  < 0.0001): the use of a pill-antagonist regimen was more frequent in the short-duration group (50.0% vs. 17.7%) and less common in the prolonged group (10.7%) compared to the reference. The type of gonadotropins did not differ significantly between groups. However, the initial gonadotropin dose also varied significantly between groups ( p  < 0.0001), with lower median dose in the short-duration group and higher dose in the prolonged group compared to the reference group. Moreover, the method of ovulation trigger also varied significantly ( p  = 0.007): hCG alone was more frequent in prolonged stimulations, while GnRH agonist use was less frequent in short stimulations. Endometrial thickness was significantly lower in the short-duration group compared to the reference (9.3 mm [7.75–10.83] vs. 10 mm [8.5–11.75]; p  = 0.0003). The number of intermediate follicles (12–15 mm) was higher in the short group and the number of follicles ≥ 16 mm was greater in the reference group whereas the prolonged group had fewer intermediate follicles, but a similar number of large follicles compared to reference. At least, the FORT index increased progressively with stimulation duration and was highest in the prolonged group ( p  < 0.0001) (Table 1 ). Table 1 Baseline characteristics of patients and cycle characteristics according to duration of ovarian stimulation (≤ 8 days, 9–13 days, ≥ 14 days) Duration of stimulation ≤ 8 days Med [IQ 25–75] or n/N (%) Duration of stimulation 9–13 days Med [IQ 25–75] or n/N(%) Duration of stimulation ≥ 14 days Med [IQ 25–75] or n/N(%) p- value* N 122 1185 149 Age (years) 34.50 [32.15–37.46] 36.08 [32.75–39] 37.42 [34.21–39.83]* 0.0004 BMI (kg/m2) 23.46 [20.74–26.72] 23.38 [20.80–26.45] 24.31 [21.10–27.69] 0.13 Smoking status 0.68  Current smoker 13/118 (11.02) 137/1142 (12) 11/141 (7.8)  Former smoker 10/118 (8.47) 88/1142 (7.71) 12/141 (8.51)  Never smoker 95/118 (80.51) 917/1142 (80.3) 118/141 (83.69) AMH (ng/mL) 2.54 [1.70–3.74]* 2.01 [1.21–3.29] 1.37 [0.79–2.47]* < 0.0001 AFC 21 [15–28]* 16 [11–23] 14 [9–19]* < 0.0001 Type of infertility 0.72  Primary (vs secondary) 86/122 (70.49) 842/1179 (71.42) 101/148 (68.24) Etiology of infertility  Unexplained infertility 56/122 (45.9) 518/1185 (43.71) 69/149 (46.31) 0.77  Tubal factor 14/122 (11.48) 212/1185 (17.89) 23/149 (15.44) 0.17  Endometriosis 22/122 (18.03) 171/1185 (14.43) 29/149 (19.46) 0.18  Ovulatory disorder 10/122 (8.2) 48/1185 (4.05) 9/149 (6.04) 0.077  Male infertility 32/122 (26.23) 336/1185 (28.35) 31/149 (20.81) 0.14 Pretreatment < 0.0001  E2 (vs pill) 61/122 (50.00)* 975/1185 (82.28) 113/149 (89.26)* Gonadotropin 0.48  FSH (vs FSH + LH) 63/122 (51.64) 633/1185 (53.42) 72/149 (48.32) Type of gonadotropin 0.51  FSHr 63/122 (51.64) 627/1185 (52.91) 71/149 (47.65)  hMG 38/122 (31.15) 335/1185 (28.27) 39/149 (26.17)  FSHr + hMG 13/122 (10.66) 135/1185 (11.39) 24/149 (16.11)  FSHr + LHr 8/122 (6.56) 88/1185 (7.43) 15/149 (10.07) Initial dose of gonadotropin 225 [200–300]* 300 [225–387.5] 300 [225–450]* < 0.0001 Total dose of gonadotropin (UI) 1800 [1490.63–2400]* 3000 [2250–3900] 4325 [3712.5–6300]* < 0.0001 Trigger method 0.007  hCGr 68/122 (55.74) 613/1185 (51.73) 95/149 (63.76)↑  GnRHa 6/122 (4.92)↓ 151/1185 (12.74) 12/149 (8.05)  Dual trigger 48/122 (39.34) 412/1185 (35.53) 42/149 (28.19) Maximal estradiol level (ng/ml) 2044 [1396–2574]* 2430 [1744–3502] 1986 [1433.5–2922.75]* < 0.0001 Endometrial thickness at trigger 9.3 [7.8–10.8]* 10 [8.5–11.8] 9.8 [8.3–11.5] 0.0003 Number of follicles between 12–15 mm at trigger 5.5 [3–9]* 4 [2–8] 3 [2–6]*  16 mm at trigger 4.5 [3–6]* 6 [3–8] 5 [3–8] 0.0003 FORT 23.08 [16.33–33.33]* 40.00 [27.27–57.14] 46.15 [34.62–69.23]* < 0.0001 AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer * Significantly different from 9–13 days group (Dunn’s test with Bonferroni correction, p  < 0.05) ↑significant over-representation (standardized residual ≥ + 2) ↓significant under-representation (standardized residual ≤ –2) Table 2 IVF and pregnancy outcomes according to duration of ovarian stimulation (≤ 8 days, 9–13 days, ≥ 14 days) Duration of stimulation ≤ 8 days Med [IQ 25–75] or n (%) Duration of stimulation 9–13 days Med [IQ 25–75] or n(%) Duration of stimulation ≥ 14 days Med [IQ 25–75] or n(%) p -value* N 122 1185 149 Number of oocytes retrieved 9 [6–13] 10 [6–14] 7 [5–12]* 0.002 Number of mature oocytes 7 [5–10] 8 [5–12] 6 [4–11]* 0.0002 Maturity rate 81.39 [62.5–92.9]* 86.67 [75.1–100] 85.71 [66.67–100] 0.001 Fertilization rate (%) 60.00 [44.44—78.93] 64.29 [45.80–77.78] 57.14 [30.95–75.96]* 0.049  ≥ 1 embryo obtained 116 (95.08) 1136 (95.86) 134 (89.93)* 0.006 Number of embryos obtained 5 [3–8] 6 [3–9] 4 [2–7]*  < 0.0001 Number of blastocyst 2 [0–4] 2 [0–4] 1 [0–3]* 0.003  ≥ 1 frozen embryo 57(46.72) 641 (54.09) 65 (43.62)* 0.023 Fresh embryo transfer 87 (71.31) 787 (66.41) 91 (61.07) 0.21 Fresh Embryo transfer (N) 87 787 91 Pregnancy rate 29 (33.33) 264 (33.55) 26 (28.57) 0.63 Ongoing pregnancy rate 20 (22.99) 217 (27.57) 20 (21.98) 0.37 Fresh embryo transfer D3 (N) 27 357 42 Pregnancy rate 9 (33.33) 100 (28.01) 13 (30.95) 0.79 Ongoing pregnancy rate 7 (25.93) 80 (22.41) 10 (23.81) 0.90 Fresh embryo transfer D5 (N) 60 430 49 Pregnancy rate 20 (33.33) 164 (38.14) 13 (26.53) 0.23 Ongoing pregnancy rate 13 (21.67) 137 (31.86) 10 (20.41) 0.08 Frozen Embryo transfer (N) 71 794 78 Ongoing pregnancy rate 23 (32.39) 214/794 (26.95) 26 (33.33) 0.33 Cumulative 110 1089 140 Cumulative ongoing pregnancy rate 39 (35.45) 406 (37.28) 43/(30.71) 0.30 * Significantly different from 9–13 days group (Dunn’s test with Bonferroni correction, p  < 0.05) Pregnancy rate: bHCG ≥ 100; Ongoing pregnancy: cardiac activity on first trimester ultrasound Table 3 Univariate and multivariate logistic regression analyses for factors associated with cumulative ongoing pregnancy rate Univariate (OR [IC95%]) p Multivariate (OR [IC95%]) p Age (vs 35—39) (years) < 0.00001 #  39 0.50 [0.41 −0.61] 0.52 [0.42—0.64] AFC (vs 14–20)  20 1.69 [1.43 −1.99] AMH (vs 1.45–2.7) (ng/ml)  2.7 1.53 [1.31- 1.79] 1.34 [1.12—1.60] BMI (vs 18.5–24.9) (kg/m 2 ) 0.41  ≤ 18.5 1.06 [0.69—1.63]  25–29.9 1.02 [0.8—1.30]  ≥ 30 0.81 [0.59—1.11] Smokers (Yes vs No) 1.03 [0.9—1.18] 0.61 FSH (FSH + LH vs FSH) 0.88 [0.79–0.98] 0.03 # 1.01 [0.86–1.19] 0.91 Pretreatment (Pill vs E2) 1.09 [1.01—1.18] 0.03 # 0.99 [0.99 −1] 0.057 FORT 0.99 [0.98 −0.99] 0.0008 # Trigger method (vs hCGr) 0.0001 #  GnRHa 1.56 [1.24—1.96]  Dual trigger 0.68 [0.57—0.82] Duration of stimulation (vs 9–13 days) 0.29 0.22  ≤ 8 days 1.04 [0.78—1.39] 0.76 [0.55 −1.06]  ≥ 14 days 0.84 [0.64—1.11] 1.14 [0.84—1.56] AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer Odd ratios (OR) with 95% confidence intervals (CI) are presented Variables with p  < 0.20 ( # ) in univariate analysis were included in the multivariate model A p value < 0.05 (*) was considered statistically significant in multivariate analysis Baseline characteristics of patients and cycle characteristics according to duration of ovarian stimulation (≤ 8 days, 9–13 days, ≥ 14 days) AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer * Significantly different from 9–13 days group (Dunn’s test with Bonferroni correction, p  < 0.05) ↑significant over-representation (standardized residual ≥ + 2) ↓significant under-representation (standardized residual ≤ –2) IVF and pregnancy outcomes according to duration of ovarian stimulation (≤ 8 days, 9–13 days, ≥ 14 days) * Significantly different from 9–13 days group (Dunn’s test with Bonferroni correction, p  < 0.05) Pregnancy rate: bHCG ≥ 100; Ongoing pregnancy: cardiac activity on first trimester ultrasound Univariate and multivariate logistic regression analyses for factors associated with cumulative ongoing pregnancy rate AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer Odd ratios (OR) with 95% confidence intervals (CI) are presented Variables with p  < 0.20 ( # ) in univariate analysis were included in the multivariate model A p value < 0.05 (*) was considered statistically significant in multivariate analysis The number of retrieved oocytes varied significantly ( p  = 0.0015), being highest in the reference group. The number of mature oocytes followed the same trend, while maturity rate was significantly lower in the short-duration group. The proportion of cycles yielding at least one embryo differed significantly, being lower in prolonged stimulation (89.9%) compared to reference (95.9%) ( p  = 0.0062). The total number of embryos, number of blastocysts, and likelihood of having at least one frozen embryo were all significantly reduced in the prolonged group. No significant difference in ongoing pregnancy rate after fresh or frozen embryo transfer was observed between groups (Table 2 ). Baseline characteristics of women who achieved or not at least one ongoing pregnancy are shown in Supplementary Table 1. Women with ongoing pregnancy were younger, had higher AMH and AFC levels, and showed stronger ovarian response markers (lower gonadotropin doses, higher FORT and number of mature oocytes). Stimulation duration did not differ significantly between groups ( p  = 0.31). In univariate analysis, younger age, higher AMH and AFC, higher FORT, and use of a pill-antagonist protocol were significantly associated with cumulative ongoing pregnancy. Women aged ≤ 35 years had higher odds compared to those aged 35–39 years (OR = 1.85 [1.58–2.17], p   39 years was associated with lower odds (OR = 0.50 [0.41–0.61], p  < 0.00001). Similarly, high AMH and AFC were associated with improved outcomes, while low E2 levels predicted lower success. Stimulation duration was not significantly associated with outcome: ≤ 8 days (OR = 1.04 [0.78–1.39]) and ≥ 14 days (OR = 0.84 [0.64–1.11]), p  = 0.29) (Table 3 ). In multivariate analysis, only age and AMH remained independently predictive. Women aged ≤ 35 years had higher odds of pregnancy (OR = 1.72 [1.44–2.05], p   39 years had lower odds (OR = 0.52 [0.42–0.64]). AMH > 2.7 ng/mL was positively associated (OR = 1.34 [1.12–1.60], p  = 0.0003), and AMH ≤ 1.45 ng/mL was negatively associated (OR = 0.70 [0.59–0.85]). After adjustment for age, AMH, stimulation protocol, and FORT index, stimulation duration was still not significantly associated with cumulative ongoing pregnancy ( p  = 0.22). Baseline characteristics of patients undergoing a fresh embryo transfer are detailed in Supplementary Table 2. In univariate analysis, younger age, higher AFC, protocol type, and day-5 transfer were significantly associated with higher chances of pregnancy. In multivariate analysis, only age remained independently predictive. Neither stimulation duration ( p  = 0.27) nor embryo transfer day ( p  = 0.1) were independently associated with pregnancy outcome after fresh embryo transfer (Table 4 ). Table 4 Univariate and multivariate logistic regression analyses for factors associated with ongoing pregnancy after fresh embryo transfer Univariate (OR [IC95%]) p Multivariate (OR [IC95%]) p Age (vs 35–39 years)   39 years 0.58 [0.46–0.76] 0.65 [0.49–0.86] AFC (vs 14–20) 0.005 # 0.34  ≤ 13 0.72 [0.59—0.88] 0.82 [0.63–1.07]  > 20 1.23 [1.00—1.52] 1.15 [0.88–1.5] AMH (vs 1.45–2.7 ng/ml) 0.08 #  ≤ 1.45 ng/ml 0.8 [0.65–0.98]  > 2.7 ng/ml 1.18 [0.96–1.45] BMI (vs 18.5–24.9 kg/m 2 ) 0.19 # 0.29  ≤ 18.5 kg/m 2 0.97 [0.53–1.79] 0.93 [0.5–1.76]  25–29.9 kg/m 2 1.19 [0.86–1.65] 1.15 [0.81–1.63]  ≥ 30 kg/m 2 0.7 [0.44–1.09] 0.73 [0.45–1.19] Smokers (Yes vs No) 1.05 [0.84–1.31] 0.67 FSH (FSH + LH vs FSH) 1.07 [0.93–1.24] 0.31 Protocol (Pill- antagonist vs E2 antagonist) 1.16 [0.97–1.38] 0.1 # Trigger method (vs hCGr) 0.09 #  GnRHa 0.87 [0.75—1.02]  Dual trigger Endometrial thickness at trigger (vs 8–9.3 mm) 0.25  ≤ 8 mm 0.86 [0.64–1.15]  9.3–10.5 mm 0.81 [0.62–1.07]  10.5–12.5 mm 1.06 [0.78–1.44]  ≥ 12 mm 1.31 [0.98–1.75] FORT 0.99 [0.98–0.99] 0.008 # 0.99 [0.98–1] 0.25 Number of mature oocytes (vs 5–10) 0.13 #   10 1.2 [0.96—1.49] Duration of stimulation (vs 9–13 days) 0.36 0.27  ≤ 8 days 0.94 [0.64–1.37] 0.75 [0.5–1.13]  ≥ 14 days 0.89 [0.61–1.29] 1.11 [0.74–1.68] Day of fresh embryo transfer (vs day 3) 1.19 [1.03–1.38] 0.01 # 1.15 [0.97–1.36] 0.1 AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer Odd ratios (OR) with 95% confidence intervals (CI) are presented Variables with p  < 0.20 (#) in univariate analysis were included in the multivariate model A p value < 0.05 (*) was considered statistically significant in multivariate analysis Univariate and multivariate logistic regression analyses for factors associated with ongoing pregnancy after fresh embryo transfer AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer Odd ratios (OR) with 95% confidence intervals (CI) are presented Variables with p  < 0.20 (#) in univariate analysis were included in the multivariate model A p value < 0.05 (*) was considered statistically significant in multivariate analysis Baseline characteristics of patients undergoing a frozen embryo transfer are detailed in Supplementary Table 3. Among patients undergoing frozen embryo transfer, ongoing pregnancy was significantly associated with younger age (at stimulation and at FET), higher AFC and AMH, and the type of endometrial preparation. Stimulation duration was not significantly associated with pregnancy outcome ( p  = 0.33). In multivariate analysis, only age at stimulation (OR = 1.6 [1.3–1.98], p  < 0.0001) and the type of endometrial preparation (OR = 0.8 [0.67–0.95], p  = 0.008) remained independently predictive of ongoing pregnancy after FET (Table 5 ). Table 5 Univariate and multivariate logistic regression analyses for factors associated with ongoing pregnancy after frozen embryo transfer Univariate (OR [IC95%]) p Multivariate (OR [IC95%]) p Age at stimulation (vs 35–39) (years)  < 0.0001 #   39 0.64 [0.47–0.86] 0.63 [0.47–0.86] Age at FET (vs 35–39) (years)   39 0.62 [0.47–0.81] AFC (vs 14–20) 0.02#  ≤ 13 0.83 [0.67–1.04]  > 20 1.31 [1.08–1.59] AMH (vs 1.45–2.7) (ng/ml) 0.02# 0.06  ≤ 1.45 0.79 [0.62–1.01] 0.82 [0.63–1.05]  > 2.7 1.3 [1.07–1.58] 1.27 [1.04–1.56] Protocol (Corpus luteal cycle vs Artificial cycle) 0.79 [0.67–0.94] 0.006# 0.8 [0.67–0.95] 0.008* Duration of stimulation (vs 9–13 days) 0.34 0.1  ≤ 8 days 1.07 [0.74–1.56] 0.91 [0.61–1.33]  ≥ 14 days 1.12 [0.78–1.61] 1.4 [0.95–2.04] AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer Odd ratios (OR) with 95% confidence intervals (CI) are presented Variables with p  < 0.20 (#) in univariate analysis were included in the multivariate model A p value < 0.05 (*) was considered statistically significant in multivariate analysis Univariate and multivariate logistic regression analyses for factors associated with ongoing pregnancy after frozen embryo transfer AFC Antral Follicle Count, AMH Anti-mullerian hormone, BMI Body Mass Index, FET Frozen Embryo Transfer Odd ratios (OR) with 95% confidence intervals (CI) are presented Variables with p  < 0.20 (#) in univariate analysis were included in the multivariate model A p value < 0.05 (*) was considered statistically significant in multivariate analysis

We conducted a retrospective, monocentric, observational study at Antoine Béclère University Hospital (Clamart, France). This study was approved by the local institutional review board (IRB approval number 2025–02) and conducted in accordance with the French legislation regarding retrospective analyses of anonymized medical data. All IVF/ICSI cycles performed between January 2019 and December 2023 using a GnRH antagonist protocol in an intra-couple infertility context were eligible. Cycles were included if performed in women aged 18 to 43 years, without preimplantation genetic testing or testicular sperm extraction. Cycles were excluded in cases of dropout before oocyte retrieval, conversion to oocyte cryopreservation due to failed sperm retrieval or contamination, and cycles performed after ovarian tissue transplantation. Since the study focused on expected normo-responders to COS, women with an extreme antral follicle count (AFC), defined as AFC ≥ 40 (indicative of polycystic ovarian morphology), or AFC < 5, consistent with POSEIDON criteria for low ovarian reserve, were also excluded [ 14 , 15 ]. Before initiating COS, most patients underwent pre-treatment with estradiol or combined estrogen-progestin pills. Estradiol was administered in the luteal phase of the preceding cycle and stopped the day before stimulation. Combined oral contraceptives were administered for 10 to 21 days, followed by a 5 to 7 days washout period. Exogenous FSH administration (recombinant FSH: Gonal F®, Merck Serono, Darmstadt, Germany; Bemfola®, Gedeon Richter, Budapest, Hungary; Ovaleap®, Teva, Ulm, Germany; highly purified hMG: Menopur®, Ferring, Saint-Prex, Switzerland; Fertistart®, Gedeon Richter, Budapest, Hungary or combined rFSH/rLH: Pergoveris®, Merck Serono, Darmstadt, Germany). Treatment was initiated in the follicular phase following hormonal assessment and ultrasound evaluation. The gonadotropin starting dose was determined by the physician according to women’s age, body mass index (BMI), antral follicle count (AFC) and anti-Müllerian hormone (AMH) levels. Follicular growth was monitored using transvaginal sonography (to assess follicle count and median size) and hormonal measurements (serum levels of estradiol, LH and progesterone). A GnRH antagonist (Ganirelix acetate: Orgalutran®, Organon, Oss, Netherlands; Fyremadel®, Ferring, Saint-Prex, Switzerland; or Cetrorelix acetate: Cetrotide®, Ferring, Saint-Prex, Switzerland) was routinely introduced on the 6th day of ovarian stimulation (S6) to prevent an LH surge [ 16 ]. Final oocyte maturation was usually performed when at least four follicles reached an average diameter of ≥ 16 mm, using recombinant hCG (Ovitrelle® 250UI, Merck Serono, Darmstadt, Germany), and/or GnRH agonist (Triptorelin acetate 0.2 mg, sc, Decapeptyl®, IPSEN Pharma, Boulogne-Billancourt, France). In high-response situations, GnRH agonist trigger was systematically favored to minimize the risk of OHSS and to avoid unnecessarily early triggering based on estradiol levels alone. Oocyte retrieval was performed 36 to 37 h later. Depending on the semen parameters, conventional IVF or ICSI were performed as previously described [ 17 ]. Embryos were cultured in a specialized medium until cleavage stage (day 2–3) or blastocyst (day 5–6). Embryo evaluation on day 2–3 embryos evaluation included the assessment of the number and regularity of blastomeres (embryonic cells) and the degree of embryonic fragmentation. Blastocysts were evaluated using the degree of expansion and the number of inner cell masses and trophoblast cells [ 18 ]. When possible, fresh embryo transfers were performed. Embryo transfers were systematically performed under transabdominal ultrasound guidance. Luteal phase support consisted in vaginal progesterone (Micronized progesterone, Progestan®, Besins Healthcare, Montrouge, France, 400 mg daily) starting on the day of oocyte retrieval and continued until the end of the first trimester in case of pregnancy. Frozen embryo transfer (FET) was performed either in the case of freeze-all strategy or after failure of fresh embryo transfer when supernumerary embryos were obtained. Only embryos reaching the blastocyst stage were vitrified as previously described [ 19 ]. In case of frozen embryo transfer, two main protocols were used for endometrial preparation: The artificial cycle protocol using hormone replacement therapy (FET-HRT) consisted in oral estradiol (Provames® 2 mg, Sanofi-Aventis, Paris, France, two tablets administered twice daily) or transdermal estradiol patches (Dermestril®, Estradiol, Rottapharm Ltd., Dublin, Ireland) in cases of contraindication to oral administration (200 µg every three days), combined with aspirin starting on the first day of menstruation. When the endometrial thickness reached ≥ 7 mm with a trilaminar pattern, vaginal progesterone supplementation was initiated (Progestan® 200 mg (Besins Healthcare, Montrouge, France) administered at a dosage of 400 mg twice a day), associated with Dydrogesterone (Duphaston®, Theramex, France) taken orally three times a day. If the endometrium did not reach this threshold, Provames® could be used with a vaginal administration. The natural, modified natural or mild stimulated cycles involve the use of the corpus luteum either by respecting the woman's natural ovulation without medical intervention (natural or modified cycles), or by inducing ovulation with gonadotrophins in case of irregular cycles or when ovulation needs to be controlled. In the modified natural and stimulated protocol and mild stimulated, ovulation was triggered as soon as the follicle exceeded 16 mm and the endometrial thickness was ≥ 7 mm. This approach allows precise scheduling of embryo transfer. The artificial cycle protocol using hormone replacement therapy (FET-HRT) consisted in oral estradiol (Provames® 2 mg, Sanofi-Aventis, Paris, France, two tablets administered twice daily) or transdermal estradiol patches (Dermestril®, Estradiol, Rottapharm Ltd., Dublin, Ireland) in cases of contraindication to oral administration (200 µg every three days), combined with aspirin starting on the first day of menstruation. When the endometrial thickness reached ≥ 7 mm with a trilaminar pattern, vaginal progesterone supplementation was initiated (Progestan® 200 mg (Besins Healthcare, Montrouge, France) administered at a dosage of 400 mg twice a day), associated with Dydrogesterone (Duphaston®, Theramex, France) taken orally three times a day. If the endometrium did not reach this threshold, Provames® could be used with a vaginal administration. The natural, modified natural or mild stimulated cycles involve the use of the corpus luteum either by respecting the woman's natural ovulation without medical intervention (natural or modified cycles), or by inducing ovulation with gonadotrophins in case of irregular cycles or when ovulation needs to be controlled. In the modified natural and stimulated protocol and mild stimulated, ovulation was triggered as soon as the follicle exceeded 16 mm and the endometrial thickness was ≥ 7 mm. This approach allows precise scheduling of embryo transfer. A serum pregnancy test (βhCG) was performed 10 or 12 days after a blastocyst or cleavage stage embryo transfer, respectively. Data were extracted from the electronic medical record (Medifirst ® software) in February 2025. Collected data included patients characteristics (age, BMI, smoking habits, menstrual cycle regularity, AFC, AMH and infertility etiology), COS parameters (ART type, pretreatment method, type of gonadotropin used, total gonadotropin dose, duration of the stimulation, number of follicles between 12–15 mm at trigger, number of follicles ≥ 16 mm the day of triggering, triggering method, estradiol peak at trigger and endometrial thickness at trigger). As indirect markers of ovarian response to ovarian stimulation, we calculated the FORT (ratio of follicles ≥ 16 mm at trigger, or follicles ≥ 14 mm adding + 2 mm the day before if no scan was available, over the AFC measured on the first day of ovarian stimulation). Data from the oocyte pickup were also collected: number of cumulo-oocyte complexes retrieved, number of mature oocytes (MII) and maturity rate (number of mature oocytes (MII) divided by the total number of retrieved oocytes), fertilization rate (defined as the ratio between the number of fertilized oocytes with two pronuclei (2PN) and the number of mature oocytes), number of embryos obtained, number of frozen embryos, number of fresh embryos transferred, and the day of transfer. For FET cycles, we collected data from the frozen embryo transfer (FET) cycle: number of cycles with FET and FET protocol. The pregnancy was defined by a positive serum β-hCG > 100. The ongoing pregnancy was defined as the presence of cardiac activity on first trimester ultrasound. The cumulative ongoing pregnancy rate (COPR) per oocyte retrieval was defined as the proportion of cycles that resulted in at least one ongoing pregnancy after fresh and/or frozen embryo transfer. Cycles were considered evaluable for the COPR calculation when either an ongoing pregnancy occurred or when all embryos generated from that retrieval had been transferred without achieving an ongoing pregnancy, including cycles with no transferable embryos. Cycles with remaining frozen embryos and no ongoing pregnancy at the time of analysis were not included in this calculation. Stimulation duration was classified as ≤ 8 days, 9–13 days (reference), or ≥ 14 days, corresponding to the ≤ 5th, 5th–95th, and ≥ 95th percentiles, respectively. Continuous variables were analyzed using the Kruskal–Wallis test. When significant, post hoc pairwise comparisons were conducted with Bonferroni correction, each group being compared to the reference group. Categorical variables were analyzed using Chi-square or Fisher’s exact tests, as appropriate. To evaluate predictive factors of ongoing pregnancy after fresh or frozen embryo transfer, or cumulative ongoing pregnancy, we first compared patients with and without ongoing pregnancy using the Mann–Whitney test for continuous variables and the Chi-square test for categorical variables. Variables were then transformed into categories based on tertiles or thresholds described in the literature, and univariate logistic regression analyses were performed. Variables with a p -value < 0.20 in univariate analysis, and without strong collinearity, were included in the multivariate logistic regression model. Stimulation duration was systematically included in the multivariate analysis regardless of its univariate significance. Results were expressed as odds ratios (OR) with 95% confidence intervals (CI). A p -value < 0.05 was considered statistically significant.

Infertility is a major public health issue, affecting approximately 15—25% of couples of reproductive age in France [ 1 ]. Assisted reproductive technologies (ART), particularly In Vitro Fertilization (IVF) with or without Intra-Cytoplasmic Sperm Injection (ICSI) plays a central role in the management of infertility and offers effective solutions across a wide range of etiologies. The success of IVF/ICSI relies on several key steps, among which controlled ovarian stimulation (COS) is essential, as it directly influences the number of oocytes retrieved and, ultimately, reproductive outcomes. During the natural menstrual cycle, follicular development occurs during the follicular phase under the influence of follicle-stimulating hormone (FSH), leading to the selection and maturation of a dominant follicle. This phase typically lasts around 12–14 days, during which rising estradiol levels secreted by the granulosa cells of the dominant follicle support endometrial proliferation [ 2 , 3 ]. Once a critical threshold is reached, estradiol triggers the luteinizing hormone (LH) surge responsible for ovulation [ 4 ]. COS aims to pharmacologically extend and amplify this follicular phase in order to promote the synchronous development of multiple follicles. The duration of this stimulated follicular phase may therefore represent a key factor influencing oocyte maturation, embryo development, and endometrial receptivity. Several COS protocols are currently used in IVF, among which the GnRH antagonist protocol is now recommended as the first-line strategy for women with normal ovarian reserve according to the current ESHRE guidelines [ 5 ]. The GnRH antagonist protocol involves the administration of gonadotropins during the follicular phase, typically over 8–14 days, to promote the recruitment and maturation of multiple follicles. Although widely used, the optimal duration of ovarian stimulation remains unclear. Compared with GnRH agonist protocols, antagonist regimens are generally associated with a shorter duration of stimulation [ 6 ]. In clinical practice, a stimulation duration of approximately 10–12 days is often considered optimal in women with normal ovarian reserve [ 7 ]. However, the literature remains inconsistent regarding the impact of stimulation duration on IVF/ICSI outcomes. While some studies reported poorer outcomes after shorter stimulation durations [ 8 , 9 ], others found no significant association [ 10 , 11 ]. Notably, many studies did not consistently focus on GnRH antagonist cycles, which may partly explain these discrepancies.. In addition, prolonged ovarian stimulation (generally ≥ 12 days), within antagonist protocols has been associated with poorer clinical outcomes, particularly lower live birth rates [ 12 ], possibly reflecting a suboptimal ovarian response or a decline in oocyte and embryo quality. Furthermore, most studies assessing the impact of stimulation duration have primarily focused on fresh embryo transfers performed on day 3 or day 5 while frozen embryo transfers are frequently excluded. Only a limited number of studies have assessed cumulative outcomes, such as cumulative ongoing pregnancy rate (COPR) or cumulative live birth rate (CLBR), which more accurately reflect the overall efficacy of a stimulation cycle [ 13 ]. The primary objective of this study was to evaluate whether the duration of ovarian stimulation in GnRH antagonist protocols influences the COPR per oocyte retrieval in women with normal ovarian reserve undergoing IVF/ICSI. Secondary objectives included the analysis of ovarian response parameters and clinical outcomes according to stimulation duration. Outcomes were evaluated separately for fresh embryo transfers and frozen blastocyst transfers.

Although no statistically significant differences were observed, our study suggests that in IVF/ICSI cycles using a GnRH antagonist protocol in women with normal ovarian reserve, a stimulation duration of 9 to 13 days may be associated with slightly more favorable biological and clinical outcomes compared to shorter or prolonged durations. However, stimulation length alone was not an independent predictor of cumulative ongoing pregnancy, reinforcing the importance of a broader, individualized assessment in clinical decision-making. These findings raise the question of whether a more refined classification of stimulation duration could help identify an optimal timing window for triggering. Prospective studies with standardized protocols—including detailed endocrine profiling and embryo assessment—are needed to validate this hypothesis and further elucidate the interaction between stimulation dynamics, endometrial receptivity, and embryo quality. Future algorithms incorporating patient characteristics (age, AMH, AFC), hormonal response, and follicular kinetics may support more personalized strategies. Artificial intelligence systems could be developed to integrate these multidimensional data and help clinicians in real-time to optimize stimulation protocols, improving both efficacy and safety in ART [ 36 ]. Importantly, our results also support the feasibility of fresh embryo transfer regardless of stimulation length, provided follicular and endometrial maturity criteria are met. In line with recent ESHRE recommendations, tailoring the timing of ovulation triggering to real-time biological parameters rather than fixed stimulation durations may optimize outcomes while maintaining safety.

In this large retrospective study of 1456 IVF/ICSI cycles using only GnRH antagonist protocol, we investigated whether the duration of ovarian stimulation influences the COPR in women with normal ovarian reserve. Stimulation cycles were categorized into three groups based on the 5 th and 95 th percentile (≤ 8 days, 9–13 days and ≥ 14 days). After adjusting for confounding variables, neither very short nor prolonged stimulation durations were significantly associated with COPR. Furthermore, multivariate analysis confirmed that stimulation duration did not impact the chance of ongoing pregnancy following either fresh or frozen embryo transfer. These findings align with those of Stout et al., who assessed CLBR, including all embryos transfer (fresh and frozen) [ 13 ]. This supports the notion that, within a GnRH antagonist protocol, stimulation length alone should not be considered a limiting factor for cumulative pregnancy success. In our cohort, age and ovarian reserve were the only independent predictive factors of COPR. When analyzed separately, age remained the primary determinant of pregnancy after fresh embryo transfer. In frozen embryo transfer cycles, age and the endometrial preparation protocol were significantly associated with outcomes. These observations are consistent with previous reports emphasizing the prognostic value of maternal age and ovarian reserve in ART [ 20 , 21 ]. Although not statistically significant, we observed a trend toward higher cumulative ongoing pregnancy rates in the group with stimulation durations of 9 to 13 days. This trend is in line with earlier studies, including Sarkar et al., who described a bell-shaped association between stimulation duration and IVF success, with optimal outcomes observed between 9 and 12 days [ 8 ]. Both shorter (≤ 8 days) and longer (≥ 13 days) stimulation durations were associated with reduced live birth rates (20.8% and 25%, respectively). Our findings suggest the existence of an optimal stimulation window, beyond which oocyte or endometrial quality may decline. We also compared women and IVF characteristics and outcomes according to ovarian stimulation duration. When comparing IVF outcomes across stimulation duration groups, prolonged stimulation (≥ 14 days) was associated with lower, though not statistically significant, rates of cumulative ongoing pregnancy and fresh transfer outcomes compared to the reference group (9–13 days). Women in this group were significantly older and had a poorer ovarian reserve, known predictors of lower ART success. As expected, the initial gonadotropin dose was higher in the prolonged stimulation group, in line with their poorer reserve parameters. Multivariate analysis confirmed that stimulation duration itself was not an independent predictor after adjustment. These findings suggest that poorer outcomes in prolonged stimulations may reflect patient characteristics rather than stimulation length per se. Similar conclusions were drawn by Aybar et al., who showed that longer stimulation duration in poor ovarian responders was associated with reduced pregnancy rates before adjustment, but not after [ 22 ]. Conversely, other studies found prolonged stimulation (≥ 13 days) to be an independent negative predictor even after adjustment [ 23 , 24 ], while Ryan et al. reported that only women with PCOS did not experience this adverse effect [ 25 ]. The initial gonadotropin dose may have contributed to the observed differences in stimulation duration. Prolonged stimulation may impair oocyte competence due to excessive gonadotropin exposure, leading to post-maturity (4), and may also disrupt endometrial receptivity via premature progesterone elevation, accelerating endometrial maturation and creating a temporal mismatch with the embryo [ 26 – 28 ]. Future research stratified by age and ovarian response is needed to elucidate whether extended stimulation affects live birth rates directly or indirectly. Short stimulations (≤ 8 days) were also associated with slightly lower, though not statistically significant, pregnancy rates (35.45% vs. 37.28% for 9–13 days). Patients in this group had higher ovarian reserve parameters, suggesting a rapid follicular response and early triggering. Their initial gonadotropin dose was lower when compared in the short stimulation group, reflecting their higher ovarian reserve . We observed a greater number of intermediate-sized follicles (12–15 mm), often associated with oocyte maturity [ 29 ], but a lower maturity rate, FORT index, and number of follicles ≥ 16 mm than in the reference group. These findings raise the possibility that accelerated follicular growth may not allow full cytoplasmic maturation despite nuclear maturity induced by hCG. This may reduce the proportion of mature oocytes and embryos. This situation might mimic for some aspects conditions observed in in vitro maturation (IVM) protocols, which are associated with lower oocyte competence [ 30 ]. Therefore, prolonging stimulation by one or two days could allow more complete in vivo maturation and possibly optimize the oocyte potential. In accordance with this hypothesis, Yoldemir et al. reported that shorter stimulation durations were associated with a higher incidence of early embryonic developmental abnormalities — including increased fragmentation and blastomere asymmetry [ 31 ] and others reported lower MII rates after ≤ 6 days of stimulation compared to 9–10 days [ 32 ]. Despite a shorter stimulation duration, the number of oocytes retrieved generally remains high which may help compensate for a potential maturation deficit. In order to reduce potential bias from extreme responders, we excluded patients with an AFC > 40 to allow for more accurate assessment of the impact of stimulation duration among normal responders. When maturity criteria are carefully applied, early triggering in rapid responders may still yield satisfactory outcomes, as supported by several studies [ 10 , 13 , 33 ]. For instance, Stout et al., reported no significant differences in clinical pregnancy or live birth rates in early responders triggered before day 9 [ 13 ] and Martin et al., found no association between stimulation duration and success, emphasizing oocyte quality instead [ 33 ]. A 2021 Cochrane review also found no difference in live birth rates between mild and conventional stimulation [ 34 ]. Another concern with short stimulation durations is their potential impact on endometrial receptivity, which can be partially assessed by endometrial thickness. An endometrial thickness < 7 mm might associated with reduced implantation rates [ 35 ], even this impact remain debates. In our study, endometrial thickness at trigger varied significantly according to stimulation duration ( p  < 0.0001). Specifically, the short stimulation group had a thinner endometrium with a median of 9 mm, compared to 10 mm in the reference group. Although 9 mm remains above the commonly accepted threshold for endometrium adequacy, this difference may reflect slightly reduced endometrial development in rapid responders. Our study presents several strengths, including a large sample size with the consistent use of the GnRH antagonist protocol across all cycles, reducing protocol-related bias. The inclusion of both fresh and frozen embryo transfers allowed for a comprehensive analysis of outcomes, providing a more realistic and reliable reflection of clinical success in ART. The study focused on the cumulative ongoing pregnancy rate as the primary outcome, which is a clinically meaningful endpoint closely correlated with live birth and increasingly favored in ART research. Also, by excluding patients with extreme phenotypes (very low ovarian reserve or PCOM), we focused on a more representative population of "normo-responders," making the conclusions applicable to a wide range of clinical scenarios. However, some limitations must be acknowledged. As a retrospective study, it is subject to selection and information bias. Baseline characteristics differed across groups, especially age and ovarian reserve, which may confound the association with stimulation duration. Although multivariate analysis adjusted for these variables, residual confounding cannot be ruled out. Moreover, although our study focused on expected normo-responders and excluded extreme ovarian reserve profiles, further studies with age-stratified analyses or alternative designs may help to better delineate the impact of stimulation duration across different responder subgroups. In addition, center-specific practices may have influenced outcomes. For example, type of endometrial preparation was associated with pregnancy outcomes, possibly reflecting local protocols. Finally, embryo quality was not systematically recorded, precluding a detailed analysis of the impact of stimulation duration on embryo competence. This represents an important area for future investigation.

Supplementary Material 1. Supplementary Material 1.