Recryopreservation (recryo) is occasionally applied in clinical, while the underlying mechanism of impaired clinical outcomes after recryo remains unclear. In this study, frozen embryo transfer (FET) cycles of single blastocyst transfer in an academic reproductive medicine center were enrolled. According to the number of times blastocysts experienced cryopreservation, they were divided into the cryopreservation (Cryo) group and the Recryo group. Donated human blastocysts were collected and detected for mechanism exploration. It was found that recryo procedure resulted in impaired blastocyst developmental potential, including decreased implantation rate, reduced biochemical pregnancy rate, declined clinical pregnancy rate, higher early miscarriage rate, and lower live birth rate. Moreover, recryo led to impaired trophectoderm (TE) function, exhibiting lower human chorionic gonadotropin levels 12 days after FET. In addition, single-cell RNA sequencing showed that the expression of genes involved in cell adhesion and embryo development were altered. More specifically, activated endoplasmic reticulum (ER) pathway and induced apoptosis were further verified by immunofluorescence and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay involving in the recryo procedure. In conclusion, recryo could interfere with the process of blastocyst implantation by impairing TE function, affecting blastocyst adhesion, activating ER stress pathway and inducing apoptosis. It provides caution to embryologists about the potential risk of recryopreservation.

OBJECTIVE: Do different timings of progesterone administration for day 5 and day 6 blastocysts affect the live birth rate (LBR) of artificial frozen embryo transfer (FET) cycles?
METHODS: This retrospective cohort study included 1362 patients who underwent artificial FET cycles. The effects of 6 and 7 days of progesterone administration prior to blastocyst transfer on clinical outcomes were compared in day 5 and day 6 blastocysts. Univariable and multivariable regression analyses were undertaken.
RESULTS: In all patients, LBR was comparable between the two groups (51.8% versus 47.9%, P = 0.165). For day 6 blastocysts, after adjusting for confounders, the 7-day progesterone regimen resulted in a significantly higher LBR (44.8% versus 36.4%, P = 0.039, adjusted OR = 1.494, 95% CI 1.060-2.106) and lower pregnancy loss rate (15.4% versus 25.2%, P = 0.031, adjusted OR = 0.472, 95% CI 0.260-0.856) compared with the 6-day progesterone regimen. For day 5 blastocysts, there were no significant differences in pregnancy outcomes between the two regimens, but the rate of low birthweight was higher with the 7-day progesterone regimen than with the 6-day progesterone regimen (13.9% versus 6.7%, P = 0.032).
CONCLUSIONS: In all blastocyst analyses, no difference in LBR was found between the 6- and 7-day progesterone regimens in artificial FET cycles. For day 6 blastocysts, LBR was significantly higher with the 7-day progesterone regimen than with the 6-day progesterone regimen, whereas for day 5 blastocysts, pregnancy outcomes were comparable between the two regimens.

UNASSIGNED: This study investigated whether RNA-Seq-based endometrial receptivity test (rsERT)-which provides precision for the optimal hour of the window of implantation (WOI)-can improve clinical outcomes of frozen embryo transfer (FET) cycles in patients with a history of repeated implantation failure (RIF).
UNASSIGNED: Patients with a history of RIF who received at least one autologous high-quality blastocyst during the subsequent FET cycle were retrospectively enrolled and divided into two groups: rsERT and FET, comprising patients who underwent rsERT-guided pET (n=115) and standard FET without rsERT (n=272), respectively.
UNASSIGNED: In the rsERT group, 39.1% (45/115) of patients were receptive. rsERT patients showed a higher probability of achieving both positive human chorionic gonadotropin (63.5% vs. 51.5%, P=0.03) and clinical pregnancy (54.8% vs. 38.6%, P=0.003) rates. In subgroup analysis, rsERT patients with non-receptive results had higher clinical pregnancy rates than patients undergoing FET (58.6% vs. 38.6%, P=0.003). rsERT patients with receptive results guided by rsERT with a precise WOI time had higher, although non-significant, clinical pregnancy rates (48.9% vs. 38.6%, P=0.192) than patients who underwent standard-time FET.
UNASSIGNED: Hourly precise rsERT can significantly improve the probability of achieving clinical pregnancy in patients with RIF, especially in those with non-receptive rsERT results.

OBJECTIVE: To investigate whether operative hysteroscopy in addition to vacuum aspiration for the management of early pregnancy loss effectively increases the success rate of subsequent frozen embryo transfer.
METHODS: Propensity score-matched cohort study.
METHODS: Women with a miscarriage at 5 to 16 gestational weeks during an IVF cycle in Peking University Third Hospital from 2015 to 2022.
METHODS: Hysteroscopy plus vacuum aspiration versus conventional vacuum aspiration.
METHODS: Live birth rate in the subsequent frozen embryo transfer.
RESULTS: 347 women who underwent vacuum aspiration plus hysteroscopy and 2,562 women who underwent conventional vacuum aspiration were included in the analysis. After propensity score matching (1:1 ratio), 325 women were included in each group. Compared to women who underwent vacuum aspiration, those who underwent vacuum aspiration plus hysteroscopy were associated with a lower rate of live birth in the propensity-based matched cohort (22% vs 30%, aOR = 0.68 (0.47, 0.97)). Biochemical, clinical and multiple pregnancy rates were not significantly different, as was miscarriage rate. In the overall cohort, 11 women experienced surgery reintervention in the vacuum aspiration group (0.4%), while no one required surgery reintervention in the vacuum aspiration plus hysteroscopy group.
CONCLUSIONS: Women who underwent vacuum aspiration plus hysteroscopy might be associated with lower rates of live birth compared to those who underwent vacuum aspiration. Further studies are necessary to establish this relationship definitively.

OBJECTIVE: To determine whether polycystic ovary syndrome (PCOS) increases adverse pregnancy and birth outcomes in women undergoing frozen embryo transfer (FET).
METHODS: Retrospective cohort study. The PCOS group was matched 1:2 with the control group population using propensity score matching (PSM).
METHODS: During an 8-year period, 2,955 patients aged 20 to 40 years who underwent FET and delivered between January 2015 and December 2022 at the Reproductive Medical Center of Ruijin Hospital were evaluated for adverse pregnancy outcomes.
METHODS: None.
METHODS: All patients were assessed for specific pregnancy complications and birth outcomes, with a sub-group analysis conducted to compare PCOS patients with and without hyperandrogenism.
RESULTS: Women with PCOS demonstrated higher rates of gestational diabetes mellitus (24.9% vs. 16.4%; relative risk (RR) 1.51 [95% confidence interval (CI): 1.26-1.82]; P <0.001), gestational hypertension (12.2% vs. 8.9%; RR 1.37 [95% CI: 1.05-1.80]; P = 0.022), preterm prelabour rupture of membranes (7.0% vs. 3.6%; RR 1.92 [95% CI: 1.29-2.86]; P = 0.001), cervical length shortening (1.8% vs. 0.4%; RR 8.39 [95% CI: 1.56-12.49]; P = 0.002), large-for-gestational age (17.4% vs. 13.7%; RR 1.27 [95% CI: 1.02-1.57]; P = 0.032), and low birth weight (19.9% vs. 16.0%; RR 1.25 [95% CI: 1.02-1.52]; P = 0.030) in overall PSM analysis. Newborns of patients with PCOS had a higher risk of preterm birth < 37 weeks (10.5% vs. 6.6%; RR 1.59 [95% CI: 1.12-2.26]; P = 0.009) in singleton pregnancies. PCOS patients with hyperandrogenism showed a higher incidence of cervical length shortening (5.5% vs. 0.5%; adjusted odds ratio (AOR) 15.62 [95% CI: 2.25-108.48]; P = 0.005) compared to those without, after adjusting for relevant confounders.
CONCLUSIONS: PCOS increases the incidence of adverse pregnancy outcomes after FET cycles. Our study suggests women with PCOS may warrant further monitoring and additional counseling before and during pregnancy.

BACKGROUND: In recent years, with benefits from the continuous improvement of clinical technology and the advantage of fertility preservation, the application of embryo cryopreservation has been growing rapidly worldwide. However, amidst this growth, concerns about its safety persist. Numerous studies have highlighted the elevated risk of perinatal complications linked to frozen embryo transfer (FET), such as large for gestational age (LGA) and hypertensive disorders during pregnancy. Thus, it is imperative to explore the potential risk of embryo cryopreservation and its related mechanisms.
METHODS: Given the strict ethical constraints on clinical samples, we employed mouse models in this study. Three experimental groups were established: the naturally conceived (NC) group, the fresh embryo transfer (Fresh-ET) group, and the FET group. Blastocyst formation rates and implantation rates were calculated post-embryo cryopreservation. The impact of FET on fetal growth was evaluated upon fetal and placental weight. Placental RNA-seq was conducted, encompassing comprehensive analyses of various comparisons (Fresh-ET vs. NC, FET vs. NC, and FET vs. Fresh-ET).
RESULTS: Reduced rates of blastocyst formation and implantation were observed post-embryo cryopreservation. Fresh-ET resulted in a significant decrease in fetal weight compared to NC group, whereas FET reversed this decline. RNA-seq analysis indicated that the majority of the expression changes in FET were inherited from Fresh-ET, and alterations solely attributed to embryo cryopreservation were moderate. Unexpectedly, certain genes that showed alterations in Fresh-ET tended to be restored in FET. Further analysis suggested that this regression may underlie the improvement of fetal growth restriction in FET. The expression of imprinted genes was disrupted in both FET and Fresh-ET groups.
CONCLUSIONS: Based on our experimental data on mouse models, the impact of embryo cryopreservation is less pronounced than other in vitro manipulations in Fresh-ET. However, the impairment of the embryonic developmental potential and the gene alterations in placenta still suggested it to be a risky operation.

OBJECTIVE: To report utilization, effectiveness, and safety of assisted reproductive technologies in 2015 and 2016.
METHODS: Retrospective, cross-sectional survey of 3103 assisted reproductive technology clinics in 74 countries in 2015 and 3249 clinics in 79 countries in 2016 that submitted cycle and pregnancy outcome data through national and regional registries.
METHODS: Patients undergoing assisted reproductive technology procedures.
METHODS: Assisted reproductive technology.
METHODS: Outcomes on country, regional, and global levels.
RESULTS: Reported for 2015: 2,358,239 cycles with 548,652 babies born; for 2016: 2,807,963 cycles with 647,188 babies born. Estimated in 2015, ≥2,683,677 cycles resulted in >675,134 babies; in 2016, ≥3,100,448 cycles resulted in ≥723,026 babies. Reported cycles represent approximately 80% of global utilization. In 2015 and 2016, 27.6% and 27.8%, respectively, of women undergoing fresh autologous cycles were age ≥40 years. Frozen-thawed embryo transfer cycles accounted for 47.0% and 51.9%, respectively, of all embryo transfers in 2015 and 2016. Oocyte donation cycles accounted for 6.7% and 7.1% of all embryo transfers in 2015 and 2016. Intracytoplasmic sperm injection was performed in 57.7% and 56.4% of autologous aspiration cycles in 2015 and 2016, respectively. The cumulative delivery rate per aspiration cycle for fresh and frozen-thawed embryo transfer was 32.4% in 2015 and 33.1% in 2016, respectively. The average number of transferred embryos was 1.70 in 2015 and 1.69 in 2016. The proportion of single embryo transfers in fresh autologous cycles increased from 42.1% in 2015 to 44.0% in 2016. The twin delivery rate decreased from 16.0% in 2015 to 14.7% in 2016, and the triplet rate decreased from 0.6% in 2015 to 0.4% in 2016. The proportion of single embryo transfers in frozen-thawed embryo transfer autologous cycles was 62.2% in 2015 and 64.2% in 2016, with twin and triplet rates of 10.1% and 0.3% in 2015 and 10.0% and 0.2% in 2016, respectively.
CONCLUSIONS: Utilization of assisted reproductive technology and births per cycle increased from 2015 to 2016 while multiple births were reduced . Increasing proportion of frozen-thawed embryo transfer cycles, continuing wide variation in use of intracytoplasmic sperm injection, and increase in single embryo transfer rates are reported.

OBJECTIVE: Does vitrification cryopreservation of embryos for more than 5 years affect the pregnancy outcomes after frozen embryo transfer (FET)?
CONCLUSIONS: Vitrification cryopreservation of good-quality blastocysts for more than 5 years is associated with a decrease in the implantation rate (IR) and live birth rate (LBR).
BACKGROUND: Previous studies have predominantly focused on embryos cryopreserved for relatively short durations (less than 5 years), yet the impact of extended cryopreservation duration on pregnancy outcomes remains a controversial issue. There is a relative scarcity of data regarding the efficacy and safety of storing embryos for 5 years or longer.
METHODS: This retrospective study involved 36 665 eligible vitrified-thawed embryo transfer cycles from 1 January 2016 to 31 December 2022, at a single fertility center in China.
METHODS: Patients were divided into three groups according to embryo storage time: Group 1 consisted of 31 565 cycles, with storage time of 0-2 years; Group 2 consisted of 4458 cycles, with a storage time of 2-5 years; and Group 3 included 642 cycles, with storage time exceeding 5 years. The main outcome measures were IR and LBR. Secondary outcome variables included rates of biochemical pregnancy, multiple pregnancy, ectopic pregnancy, and miscarriage, as well as neonatal outcomes. Reproductive outcomes were analyzed as binary variables. Multivariate logistic regression analysis was used to explore the effect of preservation time on pregnancy outcomes after correcting for confounding factors. In addition, we also assessed neonatal outcomes, such as large for gestational age (LGA) and small for gestational age (SGA).
RESULTS: IRs in the three groups (0-2, 2-5, and >5 years) were 37.37%, 39.03%, and 35.78%, respectively (P = 0.017), and LBRs in the three groups were 37.29%, 39.09%, and 34.91%, respectively (P = 0.028). After adjustment for potential confounding factors, compared with the 0-2 years storage group, prolonged embryo vitrification preservation time (2-5 years or >5 years) did not affect secondary outcomes such as rates of biochemical pregnancy, multiple pregnancy, ectopic pregnancy, and miscarriage (P > 0.05). But cryopreservation of embryos for more than 5 years reduced the IR (adjusted odds ratio (aOR) 0.82, 95% CI 0.69-0.97, P = 0.020) and LBR (aOR 0.76, 95% CI 0.64-0.91, P = 0.002). Multivariate stratified analysis also showed that prolonging the cryopreservation time of blastocysts (>5 years) reduced the IR (aOR 0.78, 95% CI 0.62-0.98, P = 0.033) and LBR (aOR 0.68, 95% CI 0.53-0.87, P = 0.002). However, no effect on cleavage embryos was observed (P > 0.05). We further conducted stratified analyses based on the number and quality of frozen blastocysts transferred, and the results showed that the FET results after transfers of good-quality blastocysts in the >5 years storage group were negatively affected. However, the storage time of non-good-quality blastocysts was not significantly associated with pregnancy outcomes. Regarding the neonatal outcomes (of singletons), embryo vitrification preservation time had no effect on preterm birth rates, fetal birth weight, or neonatal sex ratios. However, as the storage time increased, rates of SGA (5.60%, 4.10%, and 1.18%) decreased, while rates of LGA (5.22%, 6.75%, and 9.47%) increased (P < 0.05). After adjusting for confounding factors, the increase in LGA and the decrease in SGA were significantly correlated with the duration of storage time.
CONCLUSIONS: This was a retrospective study using data from a single fertility center, even though the data had been adjusted, our findings still need to be validated in further studies.
CONCLUSIONS: With the full implementation of the two-child policy in China, there may be more patients whose embryos have been frozen for a longer time in the future. Patients should be aware that the IR and LBR of blastocysts are negatively affected when the cryopreservation time is longer than 5 years. Couples may therefore consider shortening the time until FET treatment.
BACKGROUND: This study was supported by the National Nature Science Foundation of China (No. 82101672), Science and Technology Projects in Guangzhou (No. 2024A03J0180), General Guidance Program for Western Medicine of Guangzhou Municipal Health Commission (No. 20231A011096), and the Medical Key Discipline of Guangzhou (2021-2023). None of the authors have any conflicts of interest to declare.
BACKGROUND: N/A.

OBJECTIVE: This study was aimed to systematically evaluate the efficacy of artificial cycle-prepared frozen-thawed embryo transfer (FET) with or without gonadotrophin-releasing hormone agonist (GnRH-a) pretreatment for women with polycystic ovary syndrome (PCOS).
METHODS: The analysis was carried out by searching the PubMed, EMBASE, and CNKI databases with a combination of keywords before October 2021. The available studies of the effects of GnRH-a pretreatment or no pretreatment on FET in PCOS patients were considered. The risk ratios (RRs) or standardized mean differences (SMD) with 95% confidence intervals (CIs) were calculated with using subgroups and sensitivity analysis. The quality evaluation for this analysis was followed.
RESULTS: Seventeen studies including 3646 women were analyzed. GnRH-a pretreatment was significantly associated with a higher implantation rate (RR = 1.12, 95%CI: 1.00-1.24) and clinical pregnancy rate (RR = 1.19, 95%CI: 1.08-1.32) than the placebo. Moreover, in the GnRH-a pretreatment group, significant differences were detected for increasing the endometrium thickness among PCOS patients (SMD = 0.56, 95%CI: 0.20-0.92). However, for RCTs subgroup, no differences were observed, even after sensitivity analyses. In addition, the miscarriage rates, ectopic pregnancy rates, multiple pregnancy rates, and live birth rates were similar in both two groups.
CONCLUSIONS: Endometrial preparation using GnRH agonist pretreatment prior to FET seems to be the better choice for PCOS patients. However, well-designed RCTs are required for confirmation.

OBJECTIVE: To compare the pregnancy and neonatal outcomes of in vitro fertilization-embryo transfer (IVF-ET) with fresh or frozen embryos for male patients with severely low sperm count and motility.
METHODS: A total of 2300 male patients with severely low sperm count and motility underwent IVT-ET in the Reproduction Medicine Center, Sir Run Run Shaw Hospital from April 2018 to April 2022. After applying the propensity score matching (PSM), 473 fresh embryo transferred cycles and 473 frozen embryo transferred cycles were selected in the study, and the pregnancy and neonatal outcomes were compared between two groups.
RESULTS: There were no significant differences in pregnancy outcomes and neonatal outcomes between fresh and frozen embryo groups (all P>0.05). In the stratification analysis, the number of retrieved oocytes in the fresh good-quality embryo transfer group was significantly increased compared with the fresh poor-quality embryo group (P<0.05), but the very early pregnancy loss rates were similar between the two groups, while the rate in fresh good-quality embryo transfer group was significantly higher than that in the frozen good-quality embryo transfer group (P<0.05). Among different age groups of women, the number of retrieved oocytes and the level of estrogen in the fresh embryo transfer group was significantly higher in the 20 to <30 years old group than that in the 30 to <35 years old group (both P<0.05), but the clinical pregnancy rate was lower in the 20 to <30 years old group than that in the 30 to <35 years old group (P>0.05). Additionally, the very early pregnancy loss was significantly increased in the fresh embryo group compared with the frozen embryo group in the 20 to <30 years age group (P<0.05).
CONCLUSIONS: There is no significant difference in pregnancy and neonatal outcomes between fresh embryo transfer and frozen embryo transfer for male patients with severely low sperm count and motility undergoing IVF-ET. Due to shorter transfer time, less embryo freezing damage and reduced costs, fresh embryo transfer can be considered a first choice. However, it is not necessary to pursue fresh embryo transfer if maternal oestrogen levels are too high and there is a tendency of overstimulation.
目的: 评估因配偶重度少弱精子症不孕患者体外受精后移植新鲜胚胎（以下简称鲜胚移植）和冷冻胚胎（以下简称冻胚移植）的妊娠和新生儿结局，探讨该人群的最佳移植策略。方法: 收集2018年4月至2022年4月在浙江大学医学院附属邵逸夫医院生殖医学中心因男方重度少弱精子症不孕接受鲜胚和冻胚移植患者（n=2300）临床资料，如年龄、抗米勒管激素水平、移植日内膜厚度、移植胚胎等。根据移植方式分为鲜胚移植组和冻胚移植组。经过倾向性评分进行1∶1匹配后，鲜胚移植组和冻胚移植组各473例，评估两组的妊娠结局和新生儿结局。结果: 鲜胚移植组和冻胚移植组的妊娠结局和新生儿结局总体上未发现明显差异（均P>0.05）。胚胎分层分析中，全优胚胎鲜胚移植组取卵数较非优胚胎鲜胚移植组明显增加（P<0.05），但极早期妊娠丢失率两组间相近，且均明显高于全优胚胎冻胚移植组（均P<0.05）。女性不同年龄组分层分析结果显示，20~<30岁鲜胚移植组取卵数和雌激素水平均明显高于30~<35岁组（均P<0.05），但临床妊娠率略低于30~<35岁组且差异无统计学意义（P>0.05），20~<30岁鲜胚移植组的极早期妊娠丢失率较冻胚移植组明显增加（P<0.05）。结论: 因配偶重度少弱精子症不孕患者进行鲜胚移植或冻胚移植后总妊娠结局和新生儿结局无明显差异。鲜胚移植可以缩短移植时间，能避免胚胎冷冻损伤、降低费用，因此可以作为该类人群的首选移植方式。但如果母体雌激素水平过高，存在过度刺激倾向时，则不必刻意追求鲜胚移植。.