Perinatal outcomes of singletons following double vitrification-warming procedures: a retrospective study using propensity score analysis

Perinatal outcomes of singletons following double vitrification-warming procedures: a retrospective study using propensity score analysis | 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 Perinatal outcomes of singletons following double vitrification-warming procedures: a retrospective study using propensity score analysis Xiaoyue Shen, Min Ding, Yuan Yan, Chenyang Huang, Shanshan Wang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1902234/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Jan, 2023 Read the published version in BMC Pregnancy and Childbirth → Version 1 posted 13 You are reading this latest preprint version Abstract Background: Despite repeated cryopreservation is an occasional occurrence, the effect on perinatal outcomes was unclear. Therefore, the aim of this study was to evaluate the perinatal outcomes of singletons after embryo re-cryopreservation. Methods: In total, 647 live born singletons after blastocyst frozen-thawed embryo transfer cycles were investigated in this retrospective study. They were divided into two groups: the vitrified-warmed blastocysts were derived from vitrified-warmed cleavage embryos (revitrified group) or fresh cleavage embryos (once-vitrified group). Propensity score matching was used to control for potential confounding factors. Results: A total of 592 babies from once-vitrified group and 55 babies from the revitrified group. After PSM, 108 cases were generated for comparison. The median gestational age was 38 weeks for both groups and the birthweights were comparable (3390.6 ± 601.5g vs. 3412.8 ± 672.6g, P>0.05). The incidence of preterm birth (PTB) (20.4% vs. 16.7%), low birthweight (LBW) (3.7% vs. 7.4%), macrosomia (11.1% vs. 16.7%) or large for gestational age (LGA) (29.6% vs. 22.2%) was not significantly different between two groups. Logistic regression analysis indicated that double vitrification-warming procedures did not affect the occurrence of PTB (OR, 2.58 [95% CI, 0.77, 8.63]), LBW (OR, 0. 83 [0.08,8.29]), macrosomia (OR, 0.60 [0.13,2.69]), LGA (OR, 1.51 [0.53,4.27]), P>0.05. Conclusion: Our findings demonstrate that compared with once-vitrified，double vitrification-warming procedures does not increase the risk of adverse neonatal outcomes. vitrification cryopreservation frozen-thawed embryo transfer birth weight LGA Figures Figure 1 Background It has been decades since the first in vitro fertilization( IVF ) baby born, and then assisted reproduction has acquired significant advances，the number of available embryos in each IVF cycle has also increased, resulting in a slew of surplus embryo cryopreservation. Cryopreservation of embryos will increase the cumulative pregnancy rate for a single cycle of ovarian stimulation, the clinical pregnancy rate and live birth rate was be no lower than the fresh cycle, while reducing the risk of multiple pregnancies, ovarian stimulation [1-3], so cryopreservation has become a widespread reliable procedure in assisted reproductive technologies[4]. However, many studies have also shown that frozen-thawed embryo transfer （FET） increased risks of pregnancy-induced hypertension, large for gestational age, and high birth weight than fresh embryo transfer [5-7]. With the implementation of the single embryo transfer strategy, the number of surplus embryos increased[8]. In our center, in case of 2-3 embryos were frozen in one cryo-straw previously, when only one embryo was transferred, the surplus embryo will culture to blastocyst stage in vitro then refrozen by vitrification. Therefore, repeated cryopreservation procedures for surplus embryos should be considered. Most previous studies have focused on the effects of repeated freezing of embryos in pregnancy outcomes [9-11]. However, it is not clear whether embryos experiencing repeated cryopreservation process impairs perinatal outcomes. Therefore the present study aimed to evaluate the perinatal outcome of repeated cryopreservation by vitrification of human embryo at different developmental stage（from cleavage to blastocyst）. Methods Study design The medical files of all frozen-thawed blastocyst cycles from January 2013 to December 2019 at Reproductive Medicine Center of Nanjing Drum Tower Hospital were retrospectively reviewed. We established inclusion and exclusion criteria. Inclusion criteria：(1) single blastocyst transfer, (2) the patient had experienced at least one frozen-thawed cycle and had not received a live birth in the precede cycle, (3) with live singleton births and known perinatal outcomes. Exclusion criteria：(1) patients received multiple births, (2)endometriosis, (3) preimplantation genetic testing cycles, (4) history of recurrent pregnancy loss, and (5) uterine pathology. Totally 647 live born singletons were included in this study. They were divided into two groups according to the transferred blastocyst origin：vitrified-warmed blastocysts derived from fresh embryos(once-vitrified group, n=592) and vitrified-thawed cleavage embryos(revitrified-group, n=55). IVF/ICSI procedure and embryos culture Depending on the patients' age, ovarian reserve function, and ovarian responses in the previous ovulation cycle, gonadotrophin-releasing hormone agonist or antagonist protocols were used. When two to three dominant follicles reached a diameter of 18 mm, human chorionic gonadotropin (HCG) was injected. The oocytes were retrieved under transvaginal ultrasound guidance 36-38 hours after HCG administration. Retrieved oocytes were then fertilized in conventional IVF or intracytoplasmic sperm injection (ICSI). Two pronuclei and a second polar body were examined for normal fertilization at 16–18 h post-insemination. Embryos were cultured in G1/G2 sequential media (Vitrolife, Goteborg, Sweden) at 37°C in a 6% CO2, 5% O2 and 89% N2 high-humidity incubator. Blastocyst morphological evaluation was based on the Gardner scoring system. Vitrification cryopreservation and thawing procedures The vitrification cryopreservation and thawing procedures was performed in embryos，vitrification kit was produced and available at Kitazato Co., Fujinomiya, Japan. Before vitrification, the blastocyst was artificially shrunken by laser drilling. Cleavage embryos or shrunken blastocysts were equilibrated in equilibration solution for 5–8 min at room temperature, then placed into vitrification solution, 1 minute later the embryos were loaded onto the cryotop strip and plunged into liquid nitrogen immediately. For warming, the cryotop strip was removed from the liquid nitrogen and immediately transferred to thawing solution for 1 minute at 37◦C, dilution solution for 3 minutes, and then washed twice in washing solution 1 and washing solution 2 for 5 min each. After warming, embryos were cultured in embryo culture medium at 37°C in 6% CO2 for 2–4 h until transfer. Outcome Measures Overall baseline clinical characteristics for each patient included age, BMI, basal FSH，duration of infertility, parity, type of infertility and cause of infertility, and insemination methods (IVF or ICSI), and endometrium preparation protocol for FET，endometrial thickness. Any singleton birth ≥24 weeks of gestation was considered a live singleton birth. The birth weight, gestational age at delivery and gender were recorded for all live singletons. The neonatal outcomes evaluated were preterm birth (PTB, delivery between 24 and 37 weeks), low birthweight (LBW, birthweight 4000 g), average birthweight，sex ratio，small for gestational age (SGA), large for gestational age (LGA). SGA was defined as a weight below the 10th percentile for the gestational age and LGA was defined as having a birthweight greater than the 90th percentile for the gestational age at birth[12]. Statistical analysis Continuous variables were described by using mean±SD or median (interquartile range, IQR)，while categorical variables were described as absolute numbers and percentages. The data were analyzed using the Pearson's chi-squared test，Fisher's precision probability test or Student’s t-test. P-values <0.05 was considered statistically significant. 1:1Propensity score matching was used in data analysis to eliminate the influence of baseline characteristics on outcomes. The variables include maternal age, parity, basal FSH，BMI，duration of infertility, type of infertility ,parity, cause of infertility. To analyze the associations between the cryopreserved times and perinatal outcomes, logistic regression models were conducted for each outcome indicator using the before and after-matching data, and odds ratio (OR) and its 95% CI before and after adjusting for confounders were calculated. Statistical analysis was performed using SPSS statistical package version 26.0. Results Clinical characteristics and outcomes of the study cohort There were 7193 frozen-thawed single blastocyst transfer cycles were reviewed from January 2013 to December 2019 in this retrospective study. According to the inclusion and exclusion criteria, the remaining 647 cycles were analyzed（Figure1，Flowchart of the inclusion and exclusion of participants in this study）. Patients’ overall baseline demographics, baseline IVF characteristics and perinatal outcomes of the whole study population were displayed in Table 1. The female age at retrieval were 30.3±4.4 years. The average BMI and basal FSH of the study population were 22.5±3.3 kg/m 2 and 7.4±2.7 mIU/mL respectively. 75.7% patients underwent IVF, while the remaining 24.3% patients underwent ICSI. In the FET cycles, the hormone-replacement therapy (HRT) predominated in endometrium preparation (83.3%). The average birthweight for singletons was 3361.5 ± 589.3g. The preterm birth in singletons was 15.1%, rate of low birthweight and macrosomia were 5.6% and 13% respectively. The propensity score matching of basic characteristics between once-vitrified group and revitrified-group Among a total of 647 singleton live births, 55 babies resulted from revitrified-group while 592 were from once-vitrified group. The comparison of clinical characteristics between the two groups were listed in Table 2. In once-vitrified group, most of the patients were primipara (65.9%) and BMI was higher (22.5±3.4 vs. 22.2±2.7, p=0.03). In order to eliminate the influence of baseline characteristics on outcomes, a 1:1 propensity score matching was performed between the two groups. Finally, a total of 108 cases were matched by their propensity score. Before propensity score matching, two groups had significantly different characteristics but the propensity score matching balanced these characteristics between the cohorts (Table 2), suggesting the matched cohorts had highly similar baseline characteristics. Perinatal outcome s between the once-vitrified group and revitrified group before and after matching The perinatal outcomes were summarized in Table 3. No difference was observed on the birthweights between the two groups before or after marching (3356.8±582.1 g vs 3412.6±666.4 g，3390.6 ± 601.5 vs 3412.8 ± 672.6). In the once-vitrified, LBW and macrosomia was comparable to the revitrified group (P＞0.05). PTB occurred in 15.0% and 16.4% of the once-vitrified and revitrified groups respectively without significant difference. No differences were observed in terms of the infant sex ratio with boys between two matched cohorts (70.4% vs 77.8%，P>0.05). Likewise, there was no significant difference in the incidence of SGA or LGA between the two groups (P > 0.05). Modification of the cryopreservation times effect on perinatal outcomes by logistic regression models Moreover, we used logistic regression models to demonstrated the effect of double vitrification-warming procedures on perinatal outcomes. As seen in Table 4, compared to the once-vitrified group, the ORs for PTB, LBW, macrosomia and LGA in the revitrified group were 0.90 (95% CI: 0.43,1.91), 0.73 (95% CI: 0.25,2.14) ,0.74 (95% CI: 0.35,1.58) and 0.94 (95% CI: 0.49,1.81) P>0.05, before matching. After matching，the risk of being PTB, LBW ,macrosomia and LGA in the revitrified group compared to once-vitrified group were 1.28 (95% CI: 0.48,3.39), 0.48 (95% CI: 0.08,2.74) , 0.63 (95% CI: 0.21,1.90) and 1.47 (95% CI: 0.62,3.51), respectively. The adjusted outcome showed that PTB, LBW, macrosomia, LGA and birthweight was no statistical difference, adjusted for all confounding factors including the gestational age and infant gender. Discussion In this retrospective study, we assessed the effect of repeated vitrification-warming procedures on perinatal outcomes of human embryos. We found no increased risk of high birth weight and LGA singletons after repeated vitrification-warming procedures compared to once vitrification-warming procedures. More and more children are born depending on ART globally, so the safety of the offspring is more concerned. Embryo cryopreservation is a crucial part of assisted reproductive technology, and the proportion of FET had grown remarkably. In order to reduce the risk of multiple pregnancies and pregnancy complications, single embryo transfer is recommended. As multiple cleavage stage embryos might be frozen in one cryo-straw previously, after single embryo transfer, the surplus thawed embryos will be cultured to blastocyst stage and vitrified again, if this time of embryo transfer failed, these patients might choose to transfer these embryos which underwent double vitrification-warming procedures. As is known to all，compared with fresh embryo transfer，frozen embryo transfer is associated with higher risk of LGA and macrosomia in singletons [6, 13]. As well as the embryo culture period had a significant effect on the birthweight，after blastocyst stage transfer the incidence of high birth weight and LGA babies were increased[14]. However, it is not clear whether repeated frozen-thawed embryos increase the risk? Although the repeated cryopreservation of embryos is an occasional event, it is a useful method to avoid embryo wastage. The maternal and fetal health that experiences repeated freezing should be paid more attention to. There were several case reports demonstrating healthy live births after frozen thawed cycles transfer with embryos that were frozen-thawed twice [15-17]. And some retrospective studies have also shown that the embryos re-cryopreservation does not affect clinical pregnancy rates [9-11, 18]，perinatal outcomes were not described. The first follow-up study to present perinatal outcomes of children born after embryo re-cryopreservation show that human refrozen-thawed embryos resulted in normal live births after FET at a frequency comparable with that of once-frozen-thawed embryos，however, specific data on perinatal outcomes were not further analyzed[19]. A retrospective study by Lei Jin demonstrate that repeated cryopreservation will not negatively affect neonatal outcomes in singleton births[20]. In our study，patients with previous embryo transfer failure were selected in the control group，and all embryos were frozen using the same method-vitrification. Furthermore, in order to eliminate the influence of clinical baseline characteristics on results, a propensity score and logistic regression was used to control for potential confounding difference. After PSM, the Incidence of PTB, LBW, macrosomia and LGA had no difference between the once-vitrified group and the revitrified group. Logistic regression after adjusting for relevant confounding factors showed that the number of vitrification-warming procedure was not related to the Incidence of PTB, LBW, macrosomia, LGA or birthweight. The results are consistent with previous reports[19, 20]. Of course, there are several limitations in our study. First, it was a retrospective study with single-center participation. Second, although we used propensity score matching to eliminate the influence of baseline characteristics on FET outcomes as much as possible, it could not eliminate all the bias caused by confounders between the two groups. Moreover，because of the limited sample size, it was difficult to stratify the effects of repeated vitrification-warming procedures on birthweight by gender and gestational age. In addition, perinatal outcomes from fresh cycles were not included in this study, which may also create a bias. Nevertheless, the present study still presented perinatal outcomes of singletons following double vitrification-warming procedures which was occasional in the clinic, providing valuable information for clinical decision. Conclusions In summary, our results presented the neonatal safety of human refrozen-thawed embryos. Double vitrification-warming procedures of human embryos at different developmental stages do not affect perinatal outcomes. The re-cryopreservation procedure would be a valuable option to increase the cumulative pregnancy rate while preventing embryo waste under full informed consent. However, the maternal and child safety of re-cryopreservation procedure still needs to be confirmed by a long-term multicenter follow up cohort study. Abbreviations FET: frozen-thawed embryo transfer; PSM: propensity score matching; PTB: preterm birth; LBW: low birthweight; LGA: large for gestational age; SGA: small for gestational age; IVF: in-vitro fertilization; ICSI: intracytoplasmic sperm injection; BMI: body mass index; FSH: follicle-stimulating hormone; HRT: hormone-replacement therapy; HCG: human chorionic gonadotropin; IQR: interquartile range; OR: odds ratio; HRT: hormone-replacement therapy. Declarations Ethics approval and consent to participate The study received approval from the Ethics Committee of the Nanjing Drum Tower Hospital, The Affiliated Hospital to Nanjing University Medical School on 6 May 2021 (reference number 2021-163-01), which waived informed consent owing to the retrospective cohort study design. All patients did not provide written signed informed consent. All methods were conducted in compliance with relevant guidelines and regulations. Consent for publication Not applicable. Availability of data and materials The datasets generated and/or analysed during the current study are not publicly available for legal or ethical reasons, but are available from the corresponding author on reasonable request. Competing interests The authors have no conflicts of interest. Funding This work was supported by the [Jiangsu Provincial Key Research and Development Program #1] under Grant [number BE2019601]; and [National Natural Science Foundation of China] under Grant [number 81771537]. Author contributions JZ contributed to the study design. MD, JX collected data. CH, YY contributed data analysis. SW helped to perform the laboratory operations. XS was a major contributor in writing the manuscript. All authors read and approved the final manuscript. Acknowledgments The authors thank the nurses and laboratory staff of the Department of Assisted Reproduction for their assistance. References Zhang, W., X. Xiao, J. Zhang, W. Wang, J. Wu, et al., Clinical outcomes of frozen embryo versus fresh embryo transfer following in vitro fertilization: a meta-analysis of randomized controlled trials. Arch Gynecol Obstet, 2018. 298 (2): p. 259-72. Zhang, X., C. Ma, Z. Wu, L. Tao, R. Li, et al., Frozen-Thawed Embryo Transfer Cycles Have a Lower Incidence of Ectopic Pregnancy Compared With Fresh Embryo Transfer Cycles. Reprod Sci, 2018. 25 (9): p. 1431-5. Liu, X., H. Bai, W. Shi, J. Shi, Frozen-thawed embryo transfer is better than fresh embryo transfer in GnRH antagonist cycle in women with 3-10 oocytes retrieved: a retrospective cohort study. Arch Gynecol Obstet, 2019. 300 (6): p. 1791-6. Wong, K.M., S. Mastenbroek, S. Repping, Cryopreservation of human embryos and its contribution to in vitro fertilization success rates. Fertil Steril, 2014. 102 (1): p. 19-26. Smith, A., K. Tilling, D.A. Lawlor, S.M. Nelson, Live birth rates and perinatal outcomes when all embryos are frozen compared with conventional fresh and frozen embryo transfer: a cohort study of 337,148 in vitro fertilisation cycles. BMC Med, 2019. 17 (1): p. 202. Maheshwari, A., S. Pandey, E. Amalraj Raja, A. Shetty, M. Hamilton, et al., Is frozen embryo transfer better for mothers and babies? Can cumulative meta-analysis provide a definitive answer? Hum Reprod Update, 2018. 24 (1): p. 35-58. Litzky, J.F., S.L. Boulet, N. Esfandiari, Y. Zhang, D.M. Kissin, et al., Effect of frozen/thawed embryo transfer on birthweight, macrosomia, and low birthweight rates in US singleton infants. Am J Obstet Gynecol, 2018. 218 (4): p. 433 e1- e10. Cutting, R., Single embryo transfer for all. Best Pract Res Clin Obstet Gynaecol, 2018. 53 : p. 30-7. Koch, J., M.F. Costello, M.G. Chapman, S. Kilani, Twice-frozen embryos are no detriment to pregnancy success: a retrospective comparative study. Fertil Steril, 2011. 96 (1): p. 58-62. Zheng, X., Y. Chen, J. Yan, Y. Wu, X. Zhuang, et al., Effect of repeated cryopreservation on human embryo developmental potential. Reprod Biomed Online, 2017. 35 (6): p. 627-32. Farhi, J., S. Elizur, M. Yonish, D.S. Seidman, A. Shulman, et al., Assessment of a double freezing approach in the management of surplus embryos in IVF. 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Tables Table 1 Overall B aseline c linical characteristics and perinatal outcomes of the study cohort (n =647). Demographics Female age at retrieval, years 30.3±4.4 Parity Primipara 405(62.6) Multipara 242(37.4) Body mass index, kg/m 2 22.5±3.3 Basal FSH, mIU/mL 7.4±2.7 Duration of infertility, years 3.6±2.7 Type of Infertility Primary 316(48.8) Secondary 331(51.2) Cause of Infertility Ovulation disorder 40(6.2) Tubal factor 285(44.0) Male factors 68(10.5) Other factors 254(39.3) IVF characteristics Insemination method IVF 490(75.7) ICSI 157(24.3) Endometrial thickness, mm 9.4±1.7 Endometrial preparation protocol HRT 539(83.3) Ovulation induction 45（7.0） NC 63（9.7） Perinatal outcomes Gestational age, weeks 38(37-39) PTB (<37 weeks) 98（15.1） Gender Boys 361 (55.8) Girls 286 (44.2) Birthweight, g 3361.5±589.3 LBW (<2500g) 36（5.6） Macrosomia (≥4000g) 84（13） Data are presented as mean ± SD , median (IQR) and n (%). BMI, body mass index; NC, natural cycle; HRT, hormone replacement therapy; PTB, preterm birth; LBW, low birthweight; Table 2 T he propensity score matching of basic characteristics between once-vitrified group and revitrified group Before matching After matching Once-vitrified group （n=592） Revit`rified group （n=55） P Once-vitrified group （n=54） Revitrified group （n=54） P Female age at retrieval，years 30.4±4.4 29.3±4.1 0.41 29.6 ± 4.1 29.3 ± 4.2 0.71 Primipara 390(65.9) 15(27.3) ＜0.001 19(35.2) 15(27.8) 0.13 Body mass index, kg/m 2 22.5±3.4 22.2±2.7 0.03 22.4 ± 3.4 22.2 ± 2.8 0.72 Basal FSH, mIU/mL 7.5±2.8 6.5±1.5 0.06 7.1 ± 3.2 6.6 ± 1.5 0.25 Duration of infertility, years 3.5±2.7 3.7±2.5 0.43 3.8 ± 2.5 3.7 ± 2.5 0.73 Insemination method 0.44 0.82 IVF 446(75.3) 44(80.0) 41(75.9) 42(79.6) ICSI 146(24.7) 11(20.0) 13(24.1) 11(20.4) Type of Infertility 0.08 0.25 Primary 283(47.8) 33(60.0) 25 (46.3) 32 (59.3) Secondary 309(52.2) 22(40.0) 29 (53.7) 22 (40.7) Endometrial preparation protocol 0.81 0.57 HRT 491(82.9) 48(87.3) 43 (79.6) 47 (87) Ovulation induction 42(7.1) 3(5.5) 4 (7.4) 3 (5.6) NC 59(10.0) 4(7.3) 7 (13) 4 (7.4) Cause of Infertility 0.15 0.40 Ovulation disorder 38(6.4) 2(3.6) 3 (5.6) 2 (3.7) Tubal factor 253(42.7) 32(58.2) 26 (48.1) 31 (57.4) Male factors 62(10.5) 6(10.9) 3 (5.6) 6 (11.1) Other factors 239(40.4) 15(27.3) 22 (40.7) 15 (27.8) Embryo quality 0.23 0.51 High quality embryos 405(68.4) 42(76.4) 38 (70.4) 42 (77.8) Good quality embryos 187(31.6) 13(23.6) 16 (29.6) 12 (22.2) Data are presented as mean ± SD and n (%).NC: natural cycle; HRT: hormone replacement therapy. The blastocyst score was determined using Gardner blastocyst grading scale. Both the blastocyst inner cell mass and the trophectoderm cell cluster rated ≥B as high quality blastocysts；either the blastocyst inner cell mass or the trophectoderm cell cluster rated C as good quality blastocysts. Table 3 Perinatal outcomes of once-vitrified group and revitrified group before and after PS matching. Before matching After matching Once-vitrified group （n=592） Revitrified group （n=55） P Once-vitrified group（n=54） Revitrified group （n=54） P Gestational age, weeks 38(37-39) 38(37-39) 0.92 38(37-39) 38(37.7-39) 0.09 PTB (<37 weeks) 89(15.0) 9(16.4) 0.79 11 (20.4) 9 (16.7) 0.80 Neonatal abnormalities 7(1.2) 0(0.00) 1.00 0 (0.0) 0(0.00) / Birthweight, g 3356.8±582.1 3412.6±666.4 0.87 3390.6 ± 601.5 3412.8 ± 672.6 0.86 LBW (<2500 g) 32(5.4) 4(7.3) 0.56 2 (3.7) 4 (7.4) 0.67 Macrosomia (≥4000g) 75(12.7) 9(16.4) 0.44 6 (11.1) 9 (16.7) 0.58 LGA 134(22.6) 13(23.6) 0.86 16(29.6) 12(22.2) 0.38 SGA 15(2.5) 0(0) 0.63 1(1.9) 0(0) 0.49 Gender 0.45 0.51 Male 333(56.3) 28(50.9) 38 (70.4) 42 (77.8) Female 259(43.7) 27(49.1) 16 (29.6) 12 (22.2) Data are presented as mean ± SD, median (IQR) and n (%). PTB, preterm birth; LBW, low birthweight; LGA, large for gestational age; SGA,small for gestational age. Table 4 Adjusted odds ratios of PTB, LBW, macrosomia and birthweight difference （ once=1 ） Embryo vitrification-warming times PTB LBW Macrosomia Birthweight LGA OR（95%CI） P OR（95%CI） P OR（95%CI） P β（95%CI） P OR（95%CI） P Unadjusted OR before matching (n = 647) 0.90 (0.43,1.91) 0.79 0.73 (0.25,2.14) 0.56 0.74 (0.35,1.58) 0.44 55.81 (-107.39,219.01) 0.50 0.94 (0.49,1.81) 0.86 Adjusted OR before matching (n = 647) 1.06 (0.47,2.40) 0.88 0.77 (0.05,12.32) 0.85 0.67 (0.29,1.59) 0.37 40.11 (-81.66,210.17) 0.52 1.03 (0.50,2.11) 0.93 OR after matching (n =108) 1.28 (0.48,3.39) 0.62 0.48 (0.08,2.74) 0.41 0.63 (0.21,1.90) 0.41 22.28 (-221.17,265.72) 0.86 1.47 (0.62,3.51) 0.38 Adjusted after matching (n = 108) 2.58 (0.77,8.63) 0.12 0.83 (0.08,8.29) 0.88 0.60 (0.13,2.69) 0.51 1.51 (-187.74,190.77) 0.99 1.51 (0.53,4.27) 0.44 Adjusting for female retrieval age, BMI, FSH, embryo transfer cycles, parity, the type of infertility and the quality of embryos，gestational age and infant gender. β is the regression coefficient or partial regression coefficient of linear regression. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 14 Jan, 2023 Read the published version in BMC Pregnancy and Childbirth → Version 1 posted Editorial decision: Major revision 19 Oct, 2022 Reviews received at journal 18 Oct, 2022 Reviewers agreed at journal 12 Oct, 2022 Reviews received at journal 06 Oct, 2022 Reviewers agreed at journal 28 Sep, 2022 Reviewers agreed at journal 25 Sep, 2022 Reviewers agreed at journal 30 Aug, 2022 Reviewers agreed at journal 28 Aug, 2022 Reviewers invited by journal 17 Aug, 2022 Editor assigned by journal 17 Aug, 2022 Editor invited by journal 08 Aug, 2022 Submission checks completed at journal 08 Aug, 2022 First submitted to journal 27 Jul, 2022 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. 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Hospital, Nanjing University Medical School","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Min","middleName":"","lastName":"Ding","suffix":""},{"id":127285426,"identity":"28379d67-f870-4178-be95-3eecf27ee921","order_by":2,"name":"Yuan Yan","email":"","orcid":"","institution":"Drum Tower Hospital, Nanjing University Medical School","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuan","middleName":"","lastName":"Yan","suffix":""},{"id":127285427,"identity":"a4c93c6d-4754-4560-a0d0-4a6f181483fc","order_by":3,"name":"Chenyang Huang","email":"","orcid":"","institution":"Drum Tower Hospital, Nanjing University Medical School","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Chenyang","middleName":"","lastName":"Huang","suffix":""},{"id":127285429,"identity":"72e48e7f-090e-44ee-927b-2c88912dcf15","order_by":4,"name":"Shanshan Wang","email":"","orcid":"","institution":"Drum Tower Hospital, Nanjing University Medical School","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shanshan","middleName":"","lastName":"Wang","suffix":""},{"id":127285430,"identity":"52fb7187-6f0c-4460-830f-ec8aaece6ca9","order_by":5,"name":"Jianjun Zhou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+klEQVRIiWNgGAWjYDACCRA2YGBgbAAyHjAwyLGxtx8gQUsCA4MxH8+ZBMJa4ACoNnGehIMBXh3ys5uPSVgU2OUxz8g9JpHYdji9TQKo80fFNpxaGOccS5OQMEguZpyRlwbSktsm3XiAsefMbZxamCVyzIBamBMbZwAZYC0yBxKYGdtwa2GDaKmHa0lnk0gwwKuFB6LlMFxLAkEtEhJpyRYSBscTG3veGFsknEs3bAMG8kF8fpGfkXzwtsSf6sSN7TmGNz6UWcvLt7cffPCjArcWSBAACcMGBhYJRrZmsMgBvOqBgPEDyDqg1g8Mf+oIKR4Fo2AUjIIRCADeRFVDuP7VaQAAAABJRU5ErkJggg==","orcid":"","institution":"Drum Tower Hospital, Nanjing University Medical School","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Jianjun","middleName":"","lastName":"Zhou","suffix":""},{"id":127285434,"identity":"d1596aa3-d3ca-4d22-967d-659485e4be58","order_by":6,"name":"Jun Xing","email":"","orcid":"","institution":"Drum Tower Hospital, Nanjing University Medical School","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"Xing","suffix":""}],"badges":[],"createdAt":"2022-07-27 15:29:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1902234/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1902234/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12884-023-05369-z","type":"published","date":"2023-01-14T18:18:14+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":25048443,"identity":"81c04a65-a6fc-402c-b191-b285cb5ee4d8","added_by":"auto","created_at":"2022-08-10 15:58:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":22602,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of the inclusion and exclusion of participants in this study\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-1902234/v1/fe08a61919ce2173be9b9459.png"},{"id":44716749,"identity":"9bd46ae6-8295-4036-8a8c-9e051928c4b6","added_by":"auto","created_at":"2023-10-16 18:29:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":489099,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1902234/v1/679d6e78-1d04-4e93-9844-80b4052aa7e4.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Perinatal outcomes of singletons following double vitrification-warming procedures: a retrospective study using propensity score analysis","fulltext":[{"header":"Background","content":"\u003cp\u003eIt has been decades since the first in vitro fertilization( IVF ) baby born, and then assisted reproduction has acquired significant\u0026nbsp;advances，the number of available embryos in each IVF cycle has also increased, resulting in a slew of surplus embryo cryopreservation.\u0026nbsp;Cryopreservation\u0026nbsp;of embryos will increase the cumulative pregnancy rate for a single cycle of ovarian stimulation, the clinical pregnancy rate and live birth rate was be no lower than the fresh cycle, while reducing the risk of multiple pregnancies, ovarian stimulation\u0026nbsp;[1-3],\u0026nbsp;so\u0026nbsp;cryopreservation\u0026nbsp;has become a widespread reliable procedure in assisted reproductive technologies[4].\u0026nbsp;However, many studies have also shown that \u0026nbsp;frozen-thawed embryo transfer\u0026nbsp;（FET）\u0026nbsp;increased risks of pregnancy-induced hypertension, large for gestational age, and high birth weight than fresh\u0026nbsp;embryo transfer\u0026nbsp;[5-7].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWith the implementation of the single embryo transfer strategy, the number of surplus embryos increased[8]. In our center, in case of 2-3 embryos were frozen in one cryo-straw previously, when only one embryo was transferred, the surplus embryo will culture to blastocyst stage in vitro then refrozen by vitrification. Therefore, repeated cryopreservation procedures for surplus embryos should be considered. Most previous studies have focused on the effects of repeated freezing of embryos in pregnancy outcomes [9-11]. However, it is not clear whether embryos experiencing repeated cryopreservation process impairs perinatal outcomes. Therefore the present study aimed to evaluate the perinatal outcome of repeated cryopreservation by vitrification of human embryo at different developmental stage（from cleavage to blastocyst）.\u0026nbsp;\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eStudy design\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe medical files of all\u0026nbsp;frozen-thawed blastocyst cycles\u0026nbsp;from January 2013 to December 2019 at Reproductive Medicine Center of Nanjing Drum Tower Hospital were retrospectively reviewed. We established inclusion and exclusion criteria.\u0026nbsp;Inclusion criteria：(1)\u0026nbsp;single blastocyst transfer, (2) the patient\u0026nbsp;had experienced at least one frozen-thawed cycle and had not received a live birth in the\u0026nbsp;precede cycle, (3)\u0026nbsp;with live singleton births and known perinatal outcomes. Exclusion\u0026nbsp;criteria：(1)\u0026nbsp;patients received multiple births, (2)endometriosis, (3) preimplantation genetic testing cycles, (4) history of recurrent pregnancy loss, and (5) uterine pathology. Totally\u0026nbsp;647 live born\u0026nbsp;singletons\u0026nbsp;were included in this study.\u0026nbsp;They\u0026nbsp;were divided into two groups\u0026nbsp;according to the transferred blastocyst origin：vitrified-warmed blastocysts\u0026nbsp;derived from fresh embryos(once-vitrified group, n=592) \u0026nbsp;and vitrified-thawed cleavage embryos(revitrified-group, n=55).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIVF/ICSI procedure\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;and embryos culture\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDepending on the patients\u0026apos; age, ovarian reserve function, and ovarian responses in the previous ovulation cycle, gonadotrophin-releasing hormone agonist or antagonist protocols were used. When two to three dominant follicles reached a diameter of 18 mm, human chorionic gonadotropin (HCG) was injected. The oocytes were retrieved under transvaginal ultrasound guidance 36-38 hours after HCG administration. Retrieved oocytes were then fertilized in conventional IVF or intracytoplasmic sperm injection (ICSI). Two pronuclei and a second polar body were examined for normal fertilization at 16\u0026ndash;18 h post-insemination. Embryos were cultured in G1/G2 sequential media (Vitrolife, Goteborg, Sweden) at 37\u0026deg;C in a 6% CO2, 5% O2 and 89% N2 high-humidity incubator. Blastocyst morphological evaluation was based on the Gardner scoring\u0026nbsp;system.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eVitrification\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;cryopreservation and thawing procedures\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe vitrification cryopreservation and thawing procedures was\u0026nbsp;performed\u0026nbsp;in embryos，vitrification kit was produced and available\u0026nbsp;at\u0026nbsp;Kitazato Co., Fujinomiya, Japan. Before vitrification, the blastocyst was artificially shrunken by laser drilling.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCleavage embryos or shrunken\u0026nbsp;blastocysts\u0026nbsp;were equilibrated in equilibration solution for 5\u0026ndash;8 min\u0026nbsp;at room temperature, then placed into vitrification solution, 1 minute later the embryos were loaded onto the cryotop strip and\u0026nbsp;plunged into\u0026nbsp;liquid nitrogen immediately.\u0026nbsp;For warming, the cryotop strip was removed from the liquid nitrogen and immediately transferred to thawing solution for 1 minute at 37◦C, dilution solution for 3 minutes, and then washed twice in washing solution 1 and washing solution 2 for 5 min each.\u0026nbsp;After warming, embryos were cultured in embryo culture medium at 37\u0026deg;C in 6% CO2 for 2\u0026ndash;4 h until transfer.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOutcome Measures\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOverall baseline clinical characteristics\u0026nbsp;for each patient\u0026nbsp;included age, BMI,\u0026nbsp;basal FSH，duration of infertility, parity, type of infertility and cause of infertility, and insemination methods (IVF or ICSI), and endometrium preparation protocol for FET，endometrial thickness.\u003c/p\u003e\n\u003cp\u003eAny singleton birth \u0026ge;24 weeks of gestation was considered a live singleton birth.\u0026nbsp;The birth weight, gestational age at delivery and gender were recorded for all live singletons. The neonatal outcomes evaluated were preterm birth (PTB, delivery between 24 and 37 weeks), low birthweight (LBW, birthweight \u0026lt;2500 g),\u0026nbsp;macrosomia (birthweight \u0026gt;4000 g), average birthweight，sex ratio，small for gestational age\u0026nbsp;(SGA), large for gestational age (LGA). SGA was defined as a weight below the 10th percentile for the gestational age and LGA was defined as having a birthweight greater than the 90th percentile for the gestational age at birth[12].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eContinuous variables were described by using mean\u0026plusmn;SD or median (interquartile range, IQR)，while categorical variables were described as absolute numbers and percentages. The data were analyzed using the Pearson\u0026apos;s chi-squared test，Fisher\u0026apos;s precision probability test or Student\u0026rsquo;s t-test. P-values \u0026lt;0.05 was considered statistically significant. 1:1Propensity score matching was used in data analysis to eliminate the influence of baseline characteristics on outcomes. The variables include maternal age, parity, basal FSH，BMI，duration of infertility, type of infertility ,parity, cause of infertility. To analyze the associations between the cryopreserved times and perinatal outcomes, logistic regression models were conducted for each outcome indicator using the before and after-matching data, and odds ratio (OR) and its 95% CI before and after adjusting for confounders were calculated. Statistical analysis was performed using SPSS statistical package version 26.0.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eClinical characteristics and outcomes\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eof the study cohort\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere were 7193\u0026nbsp;frozen-thawed single\u0026nbsp;blastocyst\u0026nbsp;transfer cycles were reviewed from January 2013 to December 2019 in this retrospective study. According to the inclusion and exclusion criteria, the remaining 647\u0026nbsp;cycles were analyzed（Figure1，Flowchart of the inclusion and exclusion of participants in this study）.\u0026nbsp;Patients’ overall baseline demographics, baseline IVF characteristics and perinatal outcomes of the whole study population were displayed in Table 1.\u0026nbsp;The female age at retrieval were 30.3±4.4 years. The average BMI and basal FSH of the study population were 22.5±3.3 kg/m\u003csup\u003e2\u003c/sup\u003e and 7.4±2.7 mIU/mL respectively. 75.7% patients underwent IVF, while the remaining 24.3% patients underwent ICSI. In the FET cycles, the\u0026nbsp;hormone-replacement therapy (HRT)\u0026nbsp;predominated in endometrium preparation\u0026nbsp;(83.3%). The average birthweight for singletons was 3361.5 ± 589.3g. The preterm birth in singletons was 15.1%, rate of low birthweight and\u0026nbsp;macrosomia\u0026nbsp;were 5.6% and 13% respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe propensity score matching of basic characteristics between\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eonce-vitrified\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;group and\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003erevitrified-group\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAmong a total of 647 singleton live births, 55 babies resulted from revitrified-group while 592 were from once-vitrified group.\u0026nbsp;The comparison of clinical characteristics between the two groups were listed in Table 2. In once-vitrified group, most of the patients were primipara (65.9%) and BMI was higher (22.5±3.4 vs. 22.2±2.7, p=0.03).\u003c/p\u003e\n\u003cp\u003eIn order to\u0026nbsp;eliminate\u0026nbsp;the influence of baseline characteristics on outcomes, a 1:1 propensity score matching was performed between the two groups.\u0026nbsp;Finally, a total of 108 cases were matched by their propensity score. Before propensity score matching, two groups had significantly different characteristics but the propensity score matching balanced these characteristics between the cohorts (Table 2), suggesting the matched cohorts had highly similar baseline characteristics.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePerinatal\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;outcome\u003c/strong\u003e\u003cstrong\u003es\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;between the once-vitrified group and revitrified group before and after matching\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe perinatal outcomes were summarized in Table 3. No difference was observed on the birthweights\u0026nbsp;between\u0026nbsp;the two groups before or after marching (3356.8±582.1 g vs 3412.6±666.4 g，3390.6 ± 601.5 vs 3412.8 ± 672.6).\u0026nbsp;In the once-vitrified, LBW and macrosomia was comparable to the revitrified group (P＞0.05). PTB occurred in 15.0% and 16.4% of the once-vitrified and revitrified groups respectively without significant difference. No differences were observed in terms of the infant sex ratio with boys between\u0026nbsp;two matched cohorts (70.4% vs 77.8%，P\u0026gt;0.05). Likewise, there was no significant difference in the incidence of SGA or LGA between the two groups (P \u0026gt; 0.05).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eModification of the\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ecryopreservation\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;times effect on perinatal outcomes by logistic regression models\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMoreover, we used logistic regression models to demonstrated the effect of double vitrification-warming procedures on perinatal outcomes. As seen in Table 4, compared to the once-vitrified group, the ORs for PTB, LBW, macrosomia and LGA in the revitrified group were 0.90 (95% CI: 0.43,1.91), 0.73 (95% CI: 0.25,2.14) ,0.74 (95% CI: 0.35,1.58) and 0.94 (95% CI: 0.49,1.81) P\u0026gt;0.05, before matching. After matching，the risk of being PTB, LBW ,macrosomia and LGA in the revitrified group compared to once-vitrified group were 1.28 (95% CI: 0.48,3.39), 0.48 (95% CI: 0.08,2.74) , 0.63 (95% CI: 0.21,1.90) and 1.47 (95% CI: 0.62,3.51), respectively. The adjusted outcome showed that PTB, LBW, macrosomia, LGA and birthweight was no statistical difference, adjusted for all confounding factors including the gestational age and infant gender.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this retrospective study,\u0026nbsp;we assessed the effect of repeated vitrification-warming procedures on perinatal outcomes of human embryos. We found no increased risk of high birth weight and LGA singletons after repeated vitrification-warming procedures compared to once vitrification-warming procedures.\u003c/p\u003e\n\u003cp\u003eMore and more children are born depending on ART globally, so the safety of the offspring is more concerned.\u0026nbsp;Embryo cryopreservation is a crucial part of assisted reproductive technology, and\u0026nbsp;the proportion of FET had grown remarkably. In order to reduce the risk of multiple pregnancies and pregnancy complications, single embryo transfer is recommended. As\u0026nbsp;multiple cleavage stage\u0026nbsp;embryos might be\u0026nbsp;frozen in one cryo-straw previously, after single embryo transfer, the surplus thawed embryos will be cultured to blastocyst stage and vitrified again, if this time of embryo transfer failed, these patients might choose to transfer these embryos which underwent double vitrification-warming procedures.\u0026nbsp;As is known to all，compared with fresh embryo transfer，frozen embryo transfer\u0026nbsp;is associated with higher risk of LGA and macrosomia in singletons\u0026nbsp;[6, 13].\u0026nbsp;As well as the embryo culture period had a significant effect on the birthweight，after blastocyst stage transfer the incidence of high birth weight and LGA babies were increased[14].\u0026nbsp;However, it is not clear whether repeated frozen-thawed embryos increase the risk?\u0026nbsp;Although the repeated cryopreservation of embryos is an occasional event, it is a useful method to avoid embryo wastage.\u0026nbsp;The maternal and fetal health that experiences repeated freezing should be paid more attention to.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThere were several case reports demonstrating healthy live births after frozen thawed cycles transfer with embryos that were frozen-thawed twice\u0026nbsp;[15-17]. And some retrospective studies have also shown that the embryos re-cryopreservation does not affect clinical pregnancy rates\u0026nbsp;[9-11, 18]，perinatal outcomes were not described.\u0026nbsp;The first follow-up study to present perinatal outcomes of children born after embryo re-cryopreservation show that human refrozen-thawed embryos resulted in normal live births after FET at a frequency comparable with that of once-frozen-thawed embryos，however, specific\u0026nbsp;data on perinatal outcomes were not further analyzed[19]. A retrospective study by Lei Jin demonstrate that repeated cryopreservation will not negatively affect\u0026nbsp;neonatal outcomes in singleton births[20].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn our study，patients with\u0026nbsp;previous embryo transfer failure\u0026nbsp;were selected in the control group，and all embryos were frozen using the same method-vitrification.\u0026nbsp;Furthermore, in order to eliminate the influence of clinical baseline characteristics on results, a propensity score and logistic regression was used to control for potential confounding difference. After PSM, the Incidence of PTB, LBW, macrosomia and LGA had no difference between the\u0026nbsp;once-vitrified group\u0026nbsp;and\u0026nbsp;the revitrified group. Logistic regression after adjusting for relevant confounding factors showed that the number of vitrification-warming procedure was not related to the Incidence of PTB, LBW, macrosomia, LGA or birthweight. The results are consistent with previous reports[19, 20].\u003c/p\u003e\n\u003cp\u003eOf course, there are several limitations in our study. First, it was a retrospective study with single-center participation.\u0026nbsp;Second,\u0026nbsp;although we used propensity score matching to eliminate the influence of baseline characteristics on FET outcomes as much as possible, it could not eliminate all the bias caused by confounders between the two groups. Moreover，because of the limited sample size, it was difficult to stratify the effects of repeated vitrification-warming procedures on birthweight by gender and gestational age.\u0026nbsp;In addition, perinatal outcomes\u0026nbsp;from fresh cycles were not included in this study, which may also create a bias. Nevertheless, the present study still\u0026nbsp;presented\u0026nbsp;perinatal outcomes of singletons following double vitrification-warming procedures which was occasional in the clinic, providing valuable information for clinical decision.\u003c/p\u003e\n"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, our results presented the neonatal safety of human refrozen-thawed embryos. Double vitrification-warming procedures of human embryos at different developmental stages do not affect perinatal outcomes. The re-cryopreservation procedure would be a valuable option to increase the cumulative pregnancy rate while preventing embryo waste under full informed consent. However, the maternal and child safety of re-cryopreservation procedure still needs to be confirmed by a long-term multicenter follow up cohort study.\u003c/p\u003e\n"},{"header":"Abbreviations","content":"\u003cp\u003eFET: frozen-thawed embryo transfer; PSM: propensity score matching; PTB: preterm birth; LBW: low birthweight; LGA: large for gestational age; SGA: small for gestational age; IVF: in-vitro fertilization; ICSI: intracytoplasmic sperm injection; BMI: body mass index; FSH: follicle-stimulating hormone; HRT: hormone-replacement therapy; HCG: human chorionic gonadotropin; IQR: interquartile range; OR: odds ratio; HRT: hormone-replacement therapy.\u003c/p\u003e\n"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study received approval from the Ethics Committee of\u0026nbsp;the\u0026nbsp;Nanjing Drum Tower Hospital, The Affiliated Hospital to Nanjing University Medical School\u0026nbsp;on 6 May 2021 (reference number 2021-163-01), which\u0026nbsp;waived informed consent owing to the retrospective cohort study design.\u0026nbsp;All patients did not provide written signed informed consent. All methods were conducted in compliance with relevant guidelines and regulations.\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\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analysed during the current study are not publicly available for legal or ethical reasons, but are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the [Jiangsu Provincial Key Research and Development Program #1] under Grant [number BE2019601]; and [National Natural Science Foundation of China] under Grant [number 81771537].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJZ contributed to the study design. MD, JX collected\u0026nbsp;data. CH, YY contributed data analysis. SW helped to perform the laboratory operations. XS was a major contributor in writing the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank the nurses and laboratory staff of the Department of Assisted Reproduction for their assistance.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZhang, W., X. Xiao, J. Zhang, W. Wang, J. Wu, et al., \u003cem\u003eClinical outcomes of frozen embryo versus fresh embryo transfer following in vitro fertilization: a meta-analysis of randomized controlled trials.\u003c/em\u003e Arch Gynecol Obstet, 2018. \u003cstrong\u003e298\u003c/strong\u003e(2): p. 259-72.\u003c/li\u003e\n\u003cli\u003eZhang, X., C. Ma, Z. Wu, L. Tao, R. Li, et al., \u003cem\u003eFrozen-Thawed Embryo Transfer Cycles Have a Lower Incidence of Ectopic Pregnancy Compared With Fresh Embryo Transfer Cycles.\u003c/em\u003e Reprod Sci, 2018. \u003cstrong\u003e25\u003c/strong\u003e(9): p. 1431-5.\u003c/li\u003e\n\u003cli\u003eLiu, X., H. Bai, W. Shi, J. Shi, \u003cem\u003eFrozen-thawed embryo transfer is better than fresh embryo transfer in GnRH antagonist cycle in women with 3-10 oocytes retrieved: a retrospective cohort study.\u003c/em\u003e Arch Gynecol Obstet, 2019. \u003cstrong\u003e300\u003c/strong\u003e(6): p. 1791-6.\u003c/li\u003e\n\u003cli\u003eWong, K.M., S. Mastenbroek, S. Repping, \u003cem\u003eCryopreservation of human embryos and its contribution to in vitro fertilization success rates.\u003c/em\u003e Fertil Steril, 2014. \u003cstrong\u003e102\u003c/strong\u003e(1): p. 19-26.\u003c/li\u003e\n\u003cli\u003eSmith, A., K. Tilling, D.A. Lawlor, S.M. Nelson, \u003cem\u003eLive birth rates and perinatal outcomes when all embryos are frozen compared with conventional fresh and frozen embryo transfer: a cohort study of 337,148 in vitro fertilisation cycles.\u003c/em\u003e BMC Med, 2019. \u003cstrong\u003e17\u003c/strong\u003e(1): p. 202.\u003c/li\u003e\n\u003cli\u003eMaheshwari, A., S. Pandey, E. Amalraj Raja, A. Shetty, M. Hamilton, et al., \u003cem\u003eIs frozen embryo transfer better for mothers and babies? Can cumulative meta-analysis provide a definitive answer?\u003c/em\u003e Hum Reprod Update, 2018. \u003cstrong\u003e24\u003c/strong\u003e(1): p. 35-58.\u003c/li\u003e\n\u003cli\u003eLitzky, J.F., S.L. Boulet, N. Esfandiari, Y. Zhang, D.M. Kissin, et al., \u003cem\u003eEffect of frozen/thawed embryo transfer on birthweight, macrosomia, and low birthweight rates in US singleton infants.\u003c/em\u003e Am J Obstet Gynecol, 2018. \u003cstrong\u003e218\u003c/strong\u003e(4): p. 433 e1- e10.\u003c/li\u003e\n\u003cli\u003eCutting, R., \u003cem\u003eSingle embryo transfer for all.\u003c/em\u003e Best Pract Res Clin Obstet Gynaecol, 2018. \u003cstrong\u003e53\u003c/strong\u003e: p. 30-7.\u003c/li\u003e\n\u003cli\u003eKoch, J., M.F. Costello, M.G. Chapman, S. Kilani, \u003cem\u003eTwice-frozen embryos are no detriment to pregnancy success: a retrospective comparative study.\u003c/em\u003e Fertil Steril, 2011. \u003cstrong\u003e96\u003c/strong\u003e(1): p. 58-62.\u003c/li\u003e\n\u003cli\u003eZheng, X., Y. Chen, J. Yan, Y. Wu, X. Zhuang, et al., \u003cem\u003eEffect of repeated cryopreservation on human embryo developmental potential.\u003c/em\u003e Reprod Biomed Online, 2017. \u003cstrong\u003e35\u003c/strong\u003e(6): p. 627-32.\u003c/li\u003e\n\u003cli\u003eFarhi, J., S. Elizur, M. Yonish, D.S. Seidman, A. Shulman, et al., \u003cem\u003eAssessment of a double freezing approach in the management of surplus embryos in IVF.\u003c/em\u003e Reprod Biomed Online, 2019. \u003cstrong\u003e38\u003c/strong\u003e(4): p. 517-9.\u003c/li\u003e\n\u003cli\u003eZhu, L., R. Zhang, S. Zhang, W. Shi, W. Yan, et al., \u003cem\u003e[Chinese neonatal birth weight curve for different gestational age].\u003c/em\u003e Zhonghua Er Ke Za Zhi, 2015. \u003cstrong\u003e53\u003c/strong\u003e(2): p. 97-103.\u003c/li\u003e\n\u003cli\u003eSha, T., X. Yin, W. Cheng, I.Y. Massey, \u003cem\u003ePregnancy-related complications and perinatal outcomes resulting from transfer of cryopreserved versus fresh embryos in vitro fertilization: a meta-analysis.\u003c/em\u003e Fertil Steril, 2018. \u003cstrong\u003e109\u003c/strong\u003e(2): p. 330-42 e9.\u003c/li\u003e\n\u003cli\u003eMakinen, S., V. Soderstrom-Anttila, J. Vainio, A.M. Suikkari, T. Tuuri, \u003cem\u003eDoes long in vitro culture promote large for gestational age babies?\u003c/em\u003e Hum Reprod, 2013. \u003cstrong\u003e28\u003c/strong\u003e(3): p. 828-34.\u003c/li\u003e\n\u003cli\u003eYokota, Y., H. Yokota, M. Yokota, S. Sato, Y. Araki, \u003cem\u003eBirth of healthy twins from in vitro development of human refrozen embryos.\u003c/em\u003e Fertil Steril, 2001. \u003cstrong\u003e76\u003c/strong\u003e(5): p. 1063-5.\u003c/li\u003e\n\u003cli\u003eFarhat, M., B. Zentner, F. Lossos, Y. Bdolah, H. Holtzer, et al., \u003cem\u003eSuccessful pregnancy following replacement of embryos previously refrozen at blastocyst stage: case report.\u003c/em\u003e Hum Reprod, 2001. \u003cstrong\u003e16\u003c/strong\u003e(2): p. 337-9.\u003c/li\u003e\n\u003cli\u003eSmith, L.K., E.H. Roots, M.J. Dorsett, \u003cem\u003eLive birth of a normal healthy baby after a frozen embryo transfer with blastocysts that were frozen and thawed twice.\u003c/em\u003e Fertil Steril, 2005. \u003cstrong\u003e83\u003c/strong\u003e(1): p. 198-200.\u003c/li\u003e\n\u003cli\u003eSills, E.S., G.U. Murray, M.G. Genton, D.J. Walsh, G.D. Coull, et al., \u003cem\u003eClinical features and reproductive outcomes for embryos undergoing dual freeze-thaw sequences followed by blastocyst transfer: critique of 14 consecutive cases in IVF.\u003c/em\u003e Fertil Steril, 2009. \u003cstrong\u003e91\u003c/strong\u003e(4 Suppl): p. 1568-70.\u003c/li\u003e\n\u003cli\u003eMurakami, M., A. Egashira, K. Murakami, Y. Araki, T. Kuramoto, \u003cem\u003ePerinatal outcome of twice-frozen-thawed embryo transfers: a clinical follow-up study.\u003c/em\u003e Fertil Steril, 2011. \u003cstrong\u003e95\u003c/strong\u003e(8): p. 2648-50.\u003c/li\u003e\n\u003cli\u003eWang, M., J. Jiang, Q. Xi, D. Li, X. Ren, et al., \u003cem\u003eRepeated cryopreservation process impairs embryo implantation potential but does not affect neonatal outcomes.\u003c/em\u003e Reprod Biomed Online, 2021. \u003cstrong\u003e42\u003c/strong\u003e(1): p. 75-82.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e \u003cstrong\u003eOverall B\u003c/strong\u003e\u003cstrong\u003easeline\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ec\u003c/strong\u003e\u003cstrong\u003elinical characteristics and perinatal outcomes\u0026nbsp;of the study cohort (n =647).\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellpadding=\"0\" cellspacing=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003e\u003cstrong\u003eDemographics\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eFemale age at retrieval, years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e30.3\u0026plusmn;4.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eParity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003ePrimipara\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e405(62.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eMultipara\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e242(37.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eBody mass index, kg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e22.5\u0026plusmn;3.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eBasal FSH, mIU/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e7.4\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eDuration of infertility, years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e3.6\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eType\u0026nbsp;of\u0026nbsp;Infertility\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003ePrimary\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e316(48.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eSecondary\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e331(51.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eCause of Infertility\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eOvulation disorder\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e40(6.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eTubal factor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e285(44.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eMale factors\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e68(10.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eOther factors\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e254(39.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003e\u003cstrong\u003eIVF characteristics\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eInsemination method\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eIVF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e490(75.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eICSI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e157(24.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eEndometrial thickness, mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e9.4\u0026plusmn;1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eEndometrial preparation protocol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eHRT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e539(83.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eOvulation induction\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e45（7.0）\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eNC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e63（9.7）\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003e\u003cstrong\u003ePerinatal outcomes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eGestational age, weeks\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e38(37-39)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003ePTB\u0026nbsp;(\u0026lt;37 weeks)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e98（15.1）\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eGender\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eBoys\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e361 (55.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eGirls\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e286 (44.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eBirthweight, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e3361.5\u0026plusmn;589.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eLBW\u0026nbsp;(\u0026lt;2500g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e36（5.6）\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"53.535353535353536%\"\u003e\n \u003cp\u003eMacrosomia (\u0026ge;4000g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"46.464646464646464%\"\u003e\n \u003cp\u003e84（13）\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 \u0026plusmn; SD , median (IQR) and n (%). BMI, body mass index; NC, natural cycle; HRT, hormone replacement therapy; PTB, preterm birth; LBW, low birthweight;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e \u003cstrong\u003eT\u003c/strong\u003e\u003cstrong\u003ehe propensity score matching of basic characteristics between\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eonce-vitrified\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;group\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eand revitrified\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;group\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellpadding=\"0\" cellspacing=\"0\" width=\"96%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" width=\"27.551020408163264%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" width=\"36.734693877551024%\"\u003e\n \u003cp\u003eBefore matching\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" width=\"35.714285714285715%\"\u003e\n \u003cp\u003eAfter matching\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"20.28985507246377%\"\u003e\n \u003cp\u003eOnce-vitrified group\u003c/p\u003e\n \u003cp\u003e（n=592）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.840579710144926%\"\u003e\n \u003cp\u003eRevit`rified\u0026nbsp;group\u003c/p\u003e\n \u003cp\u003e（n=55）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.594202898550725%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.28985507246377%\"\u003e\n \u003cp\u003eOnce-vitrified group\u003c/p\u003e\n \u003cp\u003e（n=54）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.840579710144926%\"\u003e\n \u003cp\u003eRevitrified group\u003c/p\u003e\n \u003cp\u003e（n=54）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.144927536231885%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eFemale age at retrieval，years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e30.4\u0026plusmn;4.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e29.3\u0026plusmn;4.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e29.6 \u0026plusmn; 4.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e29.3 \u0026plusmn; 4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003ePrimipara\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e390(65.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e15(27.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e＜0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e19(35.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e15(27.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eBody mass index, kg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e22.5\u0026plusmn;3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e22.2\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e22.4 \u0026plusmn; 3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e22.2 \u0026plusmn; 2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eBasal FSH, mIU/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e7.5\u0026plusmn;2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e6.5\u0026plusmn;1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e7.1 \u0026plusmn; 3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e6.6 \u0026plusmn; 1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eDuration of\u0026nbsp;infertility, years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e3.5\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e3.7\u0026plusmn;2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e3.8 \u0026plusmn; 2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e3.7 \u0026plusmn; 2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.73\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eInsemination method\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eIVF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e446(75.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e44(80.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e41(75.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e42(79.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eICSI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e146(24.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e11(20.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e13(24.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e11(20.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eType\u0026nbsp;of\u0026nbsp;Infertility\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003ePrimary\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e283(47.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e33(60.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e25 (46.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e32 (59.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eSecondary\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e309(52.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e22(40.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e29 (53.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e22 (40.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eEndometrial preparation protocol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eHRT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e491(82.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e48(87.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e43 (79.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e47 (87)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eOvulation induction\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e42(7.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e3(5.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e4 (7.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e3 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eNC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e59(10.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e4(7.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e7 (13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e4 (7.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eCause of Infertility\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eOvulation disorder\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e38(6.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e2(3.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e3 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e2 (3.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eTubal factor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e253(42.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e32(58.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e26 (48.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e31 (57.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eMale factors\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e62(10.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e6(10.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e3 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e6 (11.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eOther factors\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e239(40.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e15(27.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e22 (40.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e15 (27.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eEmbryo quality\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eHigh\u0026nbsp;quality embryos\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e405(68.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e42(76.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e38 (70.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e42 (77.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.125%\"\u003e\n \u003cp\u003eGood\u0026nbsp;quality embryos\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e187(31.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e13(23.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003e16 (29.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\"\u003e\n \u003cp\u003e12 (22.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\"\u003e\n \u003cp\u003e\u0026nbsp;\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\u0026nbsp;\u0026plusmn;\u0026nbsp;SD and n (%).NC: natural cycle; HRT: hormone replacement therapy. The blastocyst score was determined using Gardner blastocyst grading scale. Both the blastocyst inner cell mass and the trophectoderm cell cluster rated\u0026nbsp;\u0026ge;B as\u0026nbsp;high\u0026nbsp;quality blastocysts；either the blastocyst inner cell mass or the trophectoderm cell cluster rated C as good quality blastocysts.\u0026nbsp;\u003cbr\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e \u003cstrong\u003ePerinatal outcomes of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eonce-vitrified group and revitrified group\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ebefore and after PS matching.\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"0\" cellpadding=\"0\" cellspacing=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.448979591836736%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" width=\"39.795918367346935%\"\u003e\n \u003cp\u003eBefore matching\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" width=\"37.755102040816325%\"\u003e\n \u003cp\u003eAfter matching\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003eOnce-vitrified\u0026nbsp;group\u003c/p\u003e\n \u003cp\u003e（n=592）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003eRevitrified\u0026nbsp;group\u003c/p\u003e\n \u003cp\u003e（n=55）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003eOnce-vitrified group（n=54）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eRevitrified group\u003c/p\u003e\n \u003cp\u003e（n=54）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eGestational age, weeks\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e38(37-39)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e38(37-39)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e38(37-39)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e38(37.7-39)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003ePTB\u0026nbsp;(\u0026lt;37 weeks)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e89(15.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e9(16.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e11 (20.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e9 (16.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.80\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eNeonatal abnormalities\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e7(1.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e0(0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e0(0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eBirthweight, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e3356.8\u0026plusmn;582.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e3412.6\u0026plusmn;666.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e3390.6 \u0026plusmn; 601.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e3412.8 \u0026plusmn; 672.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eLBW\u0026nbsp;(\u0026lt;2500 g)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e32(5.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e4(7.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e2 (3.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e4 (7.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eMacrosomia (\u0026ge;4000g)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e75(12.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e9(16.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e6 (11.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e9 (16.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eLGA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e134(22.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e13(23.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e16(29.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e12(22.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eSGA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e15(2.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e0(0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e1(1.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e0(0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.49\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eGender\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eMale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e333(56.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e28(50.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e38 (70.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e42 (77.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.916666666666668%\"\u003e\n \u003cp\u003eFemale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e259(43.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e27(49.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.708333333333332%\"\u003e\n \u003cp\u003e16 (29.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e12 (22.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"3.125%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eData are presented as mean \u0026plusmn; SD, median (IQR) and n (%). PTB, preterm birth; LBW, low birthweight; LGA, large for gestational age; SGA,small for gestational age.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e4\u003c/strong\u003e \u003cstrong\u003eAdjusted odds ratios of PTB, LBW, macrosomia\u0026nbsp;and birthweight difference\u003c/strong\u003e\u003cstrong\u003e（\u003c/strong\u003e\u003cstrong\u003eonce=1\u003c/strong\u003e\u003cstrong\u003e）\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellpadding=\"0\" cellspacing=\"0\" width=\"98%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" width=\"16.3265306122449%\"\u003e\n \u003cp\u003eEmbryo vitrification-warming times\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" width=\"16.3265306122449%\"\u003e\n \u003cp\u003ePTB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" width=\"16.3265306122449%\"\u003e\n \u003cp\u003eLBW\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" width=\"15.306122448979592%\"\u003e\n \u003cp\u003eMacrosomia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" width=\"20.408163265306122%\"\u003e\n \u003cp\u003eBirthweight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" width=\"15.306122448979592%\"\u003e\n \u003cp\u003eLGA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.75%\"\u003e\n \u003cp\u003eOR（95%CI）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003eOR（95%CI）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.75%\"\u003e\n \u003cp\u003eOR（95%CI）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.75%\"\u003e\n \u003cp\u003e\u0026beta;（95%CI）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003eOR（95%CI）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eUnadjusted OR before matching (n = 647)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e0.90\u003c/p\u003e\n \u003cp\u003e(0.43,1.91)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e0.73\u003c/p\u003e\n \u003cp\u003e(0.25,2.14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e0.74\u003c/p\u003e\n \u003cp\u003e(0.35,1.58)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e55.81\u003c/p\u003e\n \u003cp\u003e(-107.39,219.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e0.94\u003c/p\u003e\n \u003cp\u003e(0.49,1.81)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eAdjusted OR before matching (n = 647)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e1.06\u003c/p\u003e\n \u003cp\u003e(0.47,2.40)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e0.77\u003c/p\u003e\n \u003cp\u003e(0.05,12.32)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e0.67\u003c/p\u003e\n \u003cp\u003e(0.29,1.59)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e40.11\u003c/p\u003e\n \u003cp\u003e(-81.66,210.17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003cp\u003e(0.50,2.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eOR after matching (n =108)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e1.28\u003c/p\u003e\n \u003cp\u003e(0.48,3.39)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e0.48\u003c/p\u003e\n \u003cp\u003e(0.08,2.74)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003cp\u003e(0.21,1.90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e22.28\u003c/p\u003e\n \u003cp\u003e(-221.17,265.72)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e1.47\u003c/p\u003e\n \u003cp\u003e(0.62,3.51)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eAdjusted after matching (n = 108)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e2.58\u003c/p\u003e\n \u003cp\u003e(0.77,8.63)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003cp\u003e(0.08,8.29)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\"\u003e\n \u003cp\u003e0.60\u003c/p\u003e\n \u003cp\u003e(0.13,2.69)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003e1.51\u003c/p\u003e\n \u003cp\u003e(-187.74,190.77)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003e1.51\u003c/p\u003e\n \u003cp\u003e(0.53,4.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAdjusting for female retrieval age, BMI, FSH, embryo transfer cycles, parity, the type of infertility and the quality of embryos，gestational age and infant gender. \u0026beta;\u0026nbsp;is the regression coefficient or partial regression coefficient of linear regression.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"vitrification, cryopreservation, frozen-thawed embryo transfer, birth weight, LGA","lastPublishedDoi":"10.21203/rs.3.rs-1902234/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1902234/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003eDespite repeated cryopreservation is an occasional occurrence, the effect on perinatal outcomes was unclear. Therefore, the aim of this study was to evaluate the perinatal outcomes of singletons after embryo re-cryopreservation.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eMethods: \u003c/strong\u003eIn total, 647 live born singletons after blastocyst frozen-thawed embryo transfer cycles were investigated in this retrospective study.\u003c/p\u003e\u003cp\u003eThey were divided into two groups: the vitrified-warmed blastocysts were derived from vitrified-warmed cleavage embryos (revitrified group) or fresh cleavage embryos (once-vitrified group). Propensity score matching was used to control for potential confounding factors.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003eA total of 592 babies from once-vitrified group and 55 babies from the revitrified group. After PSM, 108 cases were generated for comparison. The median gestational age was 38 weeks for both groups and the birthweights were comparable (3390.6 ± 601.5g vs. 3412.8 ± 672.6g, P\u0026gt;0.05). The incidence of preterm birth (PTB) (20.4% vs. 16.7%), low birthweight (LBW) (3.7% vs. 7.4%), macrosomia (11.1% vs. 16.7%) or large for gestational age (LGA) (29.6% vs. 22.2%) was not significantly different between two groups. Logistic regression analysis indicated that double vitrification-warming procedures did not affect the occurrence of PTB (OR, 2.58 [95% CI, 0.77, 8.63]), LBW (OR, 0. 83 [0.08,8.29]), macrosomia (OR, 0.60 [0.13,2.69]), LGA (OR, 1.51 [0.53,4.27]), P\u0026gt;0.05. \u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e Our findings demonstrate that compared with once-vitrified，double vitrification-warming procedures does not increase the risk of adverse neonatal outcomes.\u003c/p\u003e","manuscriptTitle":"Perinatal outcomes of singletons following double vitrification-warming procedures: a retrospective study using propensity score analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-08-10 15:58:17","doi":"10.21203/rs.3.rs-1902234/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2022-10-19T10:15:08+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2022-10-18T14:23:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"868c8dce-14ae-4135-b7ed-a90e07629001","date":"2022-10-12T12:36:06+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2022-10-06T21:53:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"72bde553-e841-4b97-ac73-eed38d89e275","date":"2022-09-28T18:07:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"0e35cf75-fc85-40aa-88b9-4c75ac88216d_SNPRID","date":"2022-09-25T16:43:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"64137f0b-7735-4c5c-acc4-5f29d9d78cd4","date":"2022-08-30T16:16:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"274c1d6a-c1eb-4d8d-b31d-3df64e8b050a","date":"2022-08-28T04:18:13+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-08-17T11:42:54+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-08-17T11:16:31+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2022-08-08T11:08:01+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2022-08-08T11:02:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Pregnancy and Childbirth","date":"2022-07-27T15:19:17+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4ab9ea2e-8ca5-4103-b2f5-67b55eea7e72","owner":[],"postedDate":"August 10th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T18:25:59+00:00","versionOfRecord":{"articleIdentity":"rs-1902234","link":"https://doi.org/10.1186/s12884-023-05369-z","journal":{"identity":"bmc-pregnancy-and-childbirth","isVorOnly":false,"title":"BMC Pregnancy and Childbirth"},"publishedOn":"2023-01-14 18:18:14","publishedOnDateReadable":"January 14th, 2023"},"versionCreatedAt":"2022-08-10 15:58:17","video":"","vorDoi":"10.1186/s12884-023-05369-z","vorDoiUrl":"https://doi.org/10.1186/s12884-023-05369-z","workflowStages":[]},"version":"v1","identity":"rs-1902234","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1902234","identity":"rs-1902234","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}