Hormone replacement versus natural frozen embryo transfer for euploid embryos

Opening the black box: why do euploid blastocysts fail to implant? A systematic review and meta-analysis

BACKGROUND

A normal chromosomal constitution defined through PGT-A assessing all chromosomes on trophectoderm (TE) biopsies represents the strongest predictor of embryo implantation. Yet, its positive predictive value is not higher than 50-60%. This gap of knowledge on the causes of euploid blastocysts' reproductive failure is known as 'the black box of implantation'.

OBJECTIVE AND RATIONALE

Several embryonic, maternal, paternal, clinical, and IVF laboratory features were scrutinized for their putative association with reproductive success or implantation failure of euploid blastocysts.

SEARCH METHODS

A systematic bibliographical search was conducted without temporal limits up to August 2021. The keywords were '(blastocyst OR day5 embryo OR day6 embryo OR day7 embryo) AND (euploid OR chromosomally normal OR preimplantation genetic testing) AND (implantation OR implantation failure OR miscarriage OR abortion OR live birth OR biochemical pregnancy OR recurrent implantation failure)'. Overall, 1608 items were identified and screened. We included all prospective or retrospective clinical studies and randomized-controlled-trials (RCTs) that assessed any feature associated with live-birth rates (LBR) and/or miscarriage rates (MR) among non-mosaic euploid blastocyst transfer after TE biopsy and PGT-A. In total, 41 reviews and 372 papers were selected, clustered according to a common focus, and thoroughly reviewed. The PRISMA guideline was followed, the PICO model was adopted, and ROBINS-I and ROB 2.0 scoring were used to assess putative bias. Bias across studies regarding the LBR was also assessed using visual inspection of funnel plots and the trim and fill method. Categorical data were combined with a pooled-OR. The random-effect model was used to conduct the meta-analysis. Between-study heterogeneity was addressed using I2. Whenever not suitable for the meta-analysis, the included studies were simply described for their results. The study protocol was registered at http://www.crd.york.ac.uk/PROSPERO/ (registration number CRD42021275329).

OUTCOMES

We included 372 original papers (335 retrospective studies, 30 prospective studies and 7 RCTs) and 41 reviews. However, most of the studies were retrospective, or characterized by small sample sizes, thus prone to bias, which reduces the quality of the evidence to low or very low. Reduced inner cell mass (7 studies, OR: 0.37, 95% CI: 0.27-0.52, I2 = 53%), or TE quality (9 studies, OR: 0.53, 95% CI: 0.43-0.67, I2 = 70%), overall blastocyst quality worse than Gardner's BB-grade (8 studies, OR: 0.40, 95% CI: 0.24-0.67, I2 = 83%), developmental delay (18 studies, OR: 0.56, 95% CI: 0.49-0.63, I2 = 47%), and (by qualitative analysis) some morphodynamic abnormalities pinpointed through time-lapse microscopy (abnormal cleavage patterns, spontaneous blastocyst collapse, longer time of morula formation I, time of blastulation (tB), and duration of blastulation) were all associated with poorer reproductive outcomes. Slightly lower LBR, even in the context of PGT-A, was reported among women ≥38 years (7 studies, OR: 0.87, 95% CI: 0.75-1.00, I2 = 31%), while obesity was associated with both lower LBR (2 studies, OR: 0.66, 95% CI: 0.55-0.79, I2 = 0%) and higher MR (2 studies, OR: 1.8, 95% CI: 1.08-2.99, I2 = 52%). The experience of previous repeated implantation failures (RIF) was also associated with lower LBR (3 studies, OR: 0.72, 95% CI: 0.55-0.93, I2 = 0%). By qualitative analysis, among hormonal assessments, only abnormal progesterone levels prior to transfer were associated with LBR and MR after PGT-A. Among the clinical protocols used, vitrified-warmed embryo transfer was more effective than fresh transfer (2 studies, OR: 1.56, 95% CI: 1.05-2.33, I2 = 23%) after PGT-A. Lastly, multiple vitrification-warming cycles (2 studies, OR: 0.41, 95% CI: 0.22-0.77, I2 = 50%) or (by qualitative analysis) a high number of cells biopsied may slightly reduce the LBR, while simultaneous zona-pellucida opening and TE biopsy allowed better results than the Day 3 hatching-based protocol (3 studies, OR: 1.41, 95% CI: 1.18-1.69, I2 = 0%).

WIDER IMPLICATIONS

Embryo selection aims at shortening the time-to-pregnancy, while minimizing the reproductive risks. Knowing which features are associated with the reproductive competence of euploid blastocysts is therefore critical to define, implement, and validate safer and more efficient clinical workflows. Future research should be directed towards: (i) systematic investigations of the mechanisms involved in reproductive aging beyond de novo chromosomal abnormalities, and how lifestyle and nutrition may accelerate or exacerbate their consequences; (ii) improved evaluation of the uterine and blastocyst-endometrial dialogue, both of which represent black boxes themselves; (iii) standardization/automation of embryo assessment and IVF protocols; (iv) additional invasive or preferably non-invasive tools for embryo selection. Only by filling these gaps we may finally crack the riddle behind 'the black box of implantation'.

Obstetric and neonatal outcomes after natural versus artificial cycle frozen embryo transfer and the role of luteal phase support: a systematic review and meta-analysis

BACKGROUND

The number of frozen embryo transfers (FET) has increased dramatically over the past decade. Based on current evidence, there is no difference in pregnancy rates when natural cycle FET (NC-FET) is compared to artificial cycle FET (AC-FET) in subfertile women. However, NC-FET seems to be associated with lower risk of adverse obstetric and neonatal outcomes compared with AC-FET cycles. Currently, there is no consensus about whether NC-FET needs to be combined with luteal phase support (LPS) or not. The question of how to prepare the endometrium for FET has now gained even more importance and taken the dimension of safety into account as it should not simply be reduced to the basic question of effectiveness.

OBJECTIVE AND RATIONALE

The objective of this project was to determine whether NC-FET, with or without LPS, decreases the risk of adverse obstetric and neonatal outcomes compared with AC-FET.

SEARCH METHODS

A systematic review and meta-analysis was carried out. A literature search was performed using the following databases: CINAHL, EMBASE, and MEDLINE from inception to 10 October 2022. Observational studies, including cohort studies, and registries comparing obstetric and neonatal outcomes between singleton pregnancies after NC-FET and those after AC-FET were sought. Risk of bias was assessed using the ROBINS-I tool. The quality of evidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation approach. We calculated pooled odds ratios (ORs), pooled risk differences (RDs), pooled adjusted ORs, and prevalence estimates with 95% CI using a random effect model, while heterogeneity was assessed by the I2.

OUTCOMES

The conducted search identified 2436 studies, 890 duplicates were removed and 1546 studies were screened. Thirty studies (NC-FET n = 56 445; AC-FET n = 57 231) were included, 19 of which used LPS in NC-FET. Birthweight was lower following NC-FET versus AC-FET (mean difference 26.35 g; 95% CI 11.61-41.08, I2 = 63%). Furthermore NC-FET compared to AC-FET resulted in a lower risk of large for gestational age (OR 0.88, 95% 0.83-0.94, I2 = 54%), macrosomia (OR 0.81; 95% CI 0.71-0.93, I2 = 68%), low birthweight (OR 0.81, 95% CI 0.77-0.85, I2 = 41%), early pregnancy loss (OR 0.73; 95% CI 0.61-0.86, I2 = 70%), preterm birth (OR 0.80; 95% CI 0.75-0.85, I2 = 20%), very preterm birth (OR 0.66, 95% CI 0.53-0.84, I2 = 0%), hypertensive disorders of pregnancy (OR 0.60, 95% CI 0.50-0.65, I2 = 61%), pre-eclampsia (OR 0.50; 95% CI 0.42-0.60, I2 = 44%), placenta previa (OR 0.84, 95% CI 0.73-0.97, I2 = 0%), and postpartum hemorrhage (OR 0.43; 95% CI 0.38-0.48, I2 = 53%). Stratified analyses on LPS use in NC-FET suggested that, compared to AC-FET, NC-FET with LPS decreased preterm birth risk, while NC-FET without LPS did not (OR 0.75, 95% CI 0.70-0.81). LPS use did not modify the other outcomes. Heterogeneity varied from low to high, while quality of the evidence was very low to moderate.

WIDER IMPLICATIONS

This study confirms that NC-FET decreases the risk of adverse obstetric and neonatal outcomes compared with AC-FET. We estimate that for each adverse outcome, use of NC-FET may prevent 4 to 22 cases per 1000 women. Consequently, NC-FET should be the preferred treatment in women with ovulatory cycles undergoing FET. Based on very low quality of evidence, the risk of preterm birth be decreased when LPS is used in NC-FET compared to AC-FET. However, because of many uncertainties-the major being the debate about efficacy of the use of LPS-future research is needed on efficacy and safety of LPS and no recommendation can be made about the use of LPS.

Natural cycle frozen embryo transfer: a survey of current assisted reproductive technology practices in the U.S

PURPOSE

Emerging data suggests improved obstetric outcomes with frozen embryo transfer (FET) in an ovulatory or natural cycle (NC-FETs), as compared to programmed endometrial preparation. The objective of this study is to better understand practice patterns and provider attitudes regarding the use of NC-FETs in the United States (U.S.).

METHODS

In this cross-sectional study, an anonymous 22-question survey was emailed to 441 U.S. Assisted Reproductive Technology (ART) clinics to assess the utilization of NC endometrial preparation for FET, protocols used, restrictions to offering NC-FET, and providers' perspectives on advantages and disadvantages of NC-FET. Descriptive statistics were used to analyze survey responses.

RESULT(S)

The survey response rate was 49% (216/441). Seventeen percent of responding clinics did not offer NC-FET. Of the clinics that did not offer NC-FET, 65% had only 1-2 physicians in their practice. Common reasons for not offering NC-FET included "lack of timing predictability for transfer" (81%) and "increased burden on staff/laboratory personnel on holidays and weekends" (54%). Of clinics offering NC-FET, 76% reported < 25% of cycles used the NC for endometrial preparation. Over half (52%) of clinics that offered NC-FET reported having eligibility restrictions for NC-FET. Reported benefits of NC-FET were "patient satisfaction" (18%), "decreased cost of medications" (18%), and "avoidance of intramuscular progesterone" (17%). The attitude towards NC-FET in their clinics was reported as positive by 65% of respondents.

CONCLUSION

NC-FETs are offered by most U.S. ART clinics but are used only in the minority of FET cycles for endometrial preparation, and use is often restricted.

Risk Factors of Preterm Birth and Low Birth Weight in Singletons Conceived Through Frozen Embryo Transfer: A Retrospective Study

Background

The risks of adverse perinatal outcomes in offspring conceived following frozen-thawed embryo transfer (FET) assisted reproductive technology (ART) are inconsistent. The aim of this study was to analyze the risk factors for preterm birth and low birth weight in singletons after FET.

Methods

386 FET cycles was conducted at the Reproductive Medicine Center of Meizhou People's Hospital. The relationship between clinical characteristics and outcomes (term birth and preterm birth, normal birth weight and low birth weight) was analyzed.

Results

The rate of primary infertility, basal FSH and T levels, gestational age, birth weight, and proportion of male fetuses were significantly different in the preterm and full-term groups. Logistic regression analysis showed that high maternal age (≥35 years) (OR 3.652, 95% CI: 1.683-7.925, P=0.001), primary infertility (OR 2.869, 95% CI: 1.461-5.632, P=0.002), low FSH level (<6.215 mIU/mL) (OR 3.272, 95% CI: 1.743-6.144, P<0.001), and hormone replacement therapy (HRT) method (OR 2.780, 95% CI: 1.088-7.100, P=0.033) may increase risk of preterm birth after FET. Gestational age and birth weight were significantly different in fetuses with low birth weight (<2500g, n=38) and normal birth weight (≥2500g and <4000g, n=333). Logistic regression analysis showed that low basal FSH level (<6.215 mIU/mL) (OR 0.425, 95% CI: 0.209-0.865, P=0.018), and HRT method of endometrial preparation for FET (OR 0.272, 95% CI: 0.079-0.934, P=0.039) may reduce the risk of low birth weight after FET.

Conclusion

High maternal age, primary infertility, low FSH level, HRT method of endometrial preparation for FET, and male fetus may increase risk of preterm birth after FET. In addition, primary infertility, low basal FSH level, and HRT method of endometrial preparation may reduce the risk of low birth weight after FET.

The impact of different cycle regimens on birthweight of singletons in frozen-thawed embryo transfer cycles of ovulatory women

OBJECTIVE

To investigate whether different endometrial preparation regimens affect neonatal outcomes after frozen-thawed embryo transfer (FET).

DESIGN

Retrospective cohort study.

SETTING

Tertiary care academic medical center.

PATIENTS

A total of 3,639 patients with live-born singletons were categorized into three groups on the basis of the type of endometrial preparation regimens. Of these, 1,225, 2,136, and 278 live-born singletons were conceived through natural cycle FET, artificial cycle FET, and stimulated cycle FET, respectively.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURES

The main outcomes were the measures of birthweight including the absolute mean birthweight, Z-score, low birthweight, high birthweight (HBW), small for gestational age, and large for gestational age (LGA).

RESULTS

After controlling for a variety of covariates, singletons from the artificial cycle FET group had a higher mean birthweight and Z-score than those from the natural cycle FET group and stimulated cycle FET group. The risk of LGA infants significantly increased in the artificial cycle group (14.0%) than that in the natural cycle group (10.3%) and stimulated cycle group (7.6%). The risk of hypertensive disorders of pregnancy in the artificial cycle group (4.4%) was significantly higher than that in the natural cycle group (2.5%). The stimulated cycle FET singletons had a higher risk of low birthweight than the natural cycle FET singletons. The other perinatal outcomes, including the incidence of preterm birth, small for gestational age, and gestational diabetes mellitus, were comparable between the groups before or after adjustment for confounders.

CONCLUSIONS

Singletons from artificial cycle FET were associated with a higher risk of LGA infants, and natural cycle FET may be a better regimen for ovulatory women. Our results indicate a link between the absence of the corpus luteum and adverse perinatal outcomes, and further studies are needed to detect the underlying mechanism.

Natural cycle increases the live-birth rate compared with hormone replacement treatment for frozen-thawed single euploid blastocyst transfer

BACKGROUND

A number of studies have compared the clinical outcomes between the two endometrial preparation methods: natural cycles (NCs) and hormone replacement treatment (HRT) before frozen embryo transfer, but the results were conflicting. In order to mitigate the potential effect of embryos per se, several researchers have worked on this subject for euploid blastocyst transfer, but the results were still inconsistent. Therefore, the present study was aimed to investigate the clinical outcomes between HRT and NC for autologous single vitrified-warmed euploid blastocyst transfer based on our data.

METHODS

A total of 598 frozen-thawed single euploid blastocyst transfer cycles in the assisted reproductive center of Northwest Women's and Children's Hospital from January 2014 to May 2021 were retrospectively analyzed. Women were stratified into the NC (n = 125) or HRT (n = 473) group according to the patient's preference and the physician's guidance. Multivariate regression models and subgroup analysis were constructed to analyze the association between endometrial preparation and live birth.

RESULTS

Women in the NC group had a higher live birth rate (68.80% versus 58.35%, P = 0.034) and a lower risk of total pregnancy loss (8.51% versus 21.14%, P = 0.005) when compared with women in the HRT group. The biochemical pregnancy rate (75.20% versus 74.00%, P = 0.784) and clinical pregnancy rate (74.40% versus 69.98%, P = 0.334) were similar between the two groups (NC versus HRT). NC was associated with an increased odds of live birth compared with HRT by different multivariable analysis models (Model 1: adjusted odds ratio [aOR], 95% confidence interval [CI]: 0.57, 0.36 - 0.90; Model 2: aOR, 95%CI: 0.57, 0.35 - 0.92). In addition, the increased chance of live birth in the NC group was found in all subgroups. No major obstetrical complications and two malformation livebirths were reported.

CONCLUSIONS

In women undergoing single euploid frozen blastocyst transfers, the NC group was associated with a lower pregnancy loss rate and an ultimately higher live birth rate than the HRT group. Although HRT is convenient for both clinicians and patients, the lower live birth rate should be taken into account and NC might be the first choice of endometrial preparation method.

Pregnancy Outcomes After Frozen-Thawed Embryo Transfer in the Absence of a Corpus Luteum

Background: Nowadays, frozen-thawed embryo transfer (FET) cycles represent a high proportion of fertility treatments worldwide. Recent studies suggest differences in pregnancy outcomes depending on the FET treatment protocol used. The reason for this is still unclear, but the number of corpora lutea (CL) at conception is discussed as a possible factor. This study aims to investigate whether maternal and neonatal outcomes for pregnancies following FET lacking a CL differ from FET with one or more CL in order to explore a potential link between CL absence and adverse pregnancy outcomes.

Methods: The study was designed as a retrospective, multi-center observational study with two cohorts after singleton live birth [0 CL cohort (FET in a programmed cycle, n = 114) and ≥ 1 CL cohort (FET in a natural or stimulated cycle, n = 68)]. Participants completed a questionnaire on the outcome of pregnancy and birth records were analyzed in a descriptive way. Multivariable logistic and linear regressions were performed in order to explore associations between CL absence and pregnancy outcomes. The strength of the agreement between the information in the survey and the diagnoses extracted from the files was assessed by Cohen's Kappa.

Results: The risk of hypertensive disorders of pregnancy was higher after FET in the absence of a CL compared to FET with CL presence (aOR 5.56, 95% CI 1.12 – 27.72). Birthweights and birthweight percentiles were significantly higher in the 0 CL group. CL absence was a predictor of higher birthweight (adjusted coefficient B 179.74, 95% CI 13.03 – 346.44) and higher birthweight percentiles (adjusted coefficient B 10.23, 95%, 95% CI 2.28 – 18.40) particularly in female newborns of the 0 CL cohort. While the strength of the agreement between the reported information in the survey and the actual diagnoses extracted from the files was good for the majority of outcomes of interest it was fair in terms of hypertension (κ = 0.38).

Conclusion: This study supports observations suggesting a potential link between a lack of CL at conception and adverse maternal and neonatal outcomes. Further investigations on causes and pathophysiological relationships are yet to be conducted.

Live birth rates after natural cycle versus hormone replacement therapy for single euploid blastocyst transfers: a retrospective cohort study

RESEARCH QUESTION

Is there any difference in live birth rate between the natural cycle and hormone replacement therapy (HRT) endometrial preparation protocols for women with regular menstrual cycles undergoing their first single vitrified-warmed euploid blastocyst transfer?

DESIGN

This was a retrospective cohort study that enrolled 722 women who underwent vitrified-warmed euploid blastocyst transfer at assisted reproductive technology (ART) centre of The First Affiliated Hospital of Zhengzhou University, from January 2013 to December 2019. Univariate and multivariate logistic regression models were used to analyse the relationship between the endometrial preparation protocols and live birth rates. Stratified analyses and sensitivity analyses were performed to ensure the reliability and stability of the results.

RESULTS

A total of 722 single vitrified-warmed euploid blastocyst transfer cycles were included. Overall, the live birth rates were 50.00% (110/220) in the natural cycle group and 47.61% (239/502) in the HRT group. Multiple logistic regression analyses showed that there was no significant association (adjusted odds ratio 0.82; 95% confidence interval 0.56-1.20; P = 0.313) between natural cycle and HRT protocols and the live birth rate. Interaction analysis showed that there was no significant difference in live birth rates between the two groups for any subgroup after adjusting for confounding factors.

CONCLUSIONS

For single vitrified-warmed euploid blastocyst transfer, natural cycle and HRT endometrial preparation protocols result in similar live birth rates among women with regular menstrual cycles. Further studies are needed into the effects of endometrial preparation protocols on pregnancy outcomes.

Natural cycle versus hormone replacement cycle for transferring vitrified-warmed embryos in eumenorrhoeic women. A retrospective cohort study

OBJECTIVE

To compare pregnancy, miscarriage and live birth rates and cycle monitoring parameters between Natural Cycle (NC-FET) and Hormone replacement cycle (HRC-FET) in eumenorrhoeic women undergoing vitrified-warmed autologous embryo transfer.

STUDY DESIGN

Single-centre retrospective cohort study analyzed 173 NC-FET and 507 HRC-FET cycles with transfer of day2/3/5/6 embryos. Natural cycle monitoring occurred with serial ultrasound with the first day of the scan determined by the shortest cycle frequency. Serum progesterone was ordered when ultrasound was ambiguous in ascertaining ovulation. For HRC-FET oral estradiol valerate was used in fixed or escalating doses with maximum daily dose of 12 mg. Transdermal estradiol gel was added when desired endometrial thickness was not achieved. Vaginal progesterone was introduced with Endometrial thickness(ET)> = 7 mm. Embryos were transferred after stage-appropriate progesterone exposure. Luteal support was given with vaginal progesterone in NC-FET and vaginal and oral progesterone in HRC-FET. Primary outcome was live-birth-rate. Secondary outcomes were ET, length-of-estrogenic-phase, numbers-of-ultrasounds&hormone-monitoring, pregnancy&miscarriage rate. The odds ratio for live-birth was adjusted for age, embryo number, previous-live-births, previous-losses, past-negative-ET-cycles, IVF-indication and embryo-developmental-stage. Quantitative variables were compared using unpaired-t-test and qualitative variables with chi-square test. Two tailed p-value < 0.05 was considered significant. Binary logistic regression was used to calculate adjusted odds for live-births.

RESULTS

The two cohorts were comparable in age, infertility-duration, previous-live-births, previous-losses, past-negative-ET-cycles, IVF-indication and embryo-developmental-stage. Length-of-estrogenic-phase was significantly shorter for NC-FET than HRC-FET 14.32 ± 2.83vs.18.18 ± 4.48; p = 0.0001) as was mean ultrasound-monitoring-scans (2.73 ± 0.95vs. 3.3 ± 1.04; p = 0.0001). Mean-endometrial-thickness (8.75 ± 1.83vs. 8.5 ± 1.25; p = 0.25) and mean-hormonal-tests (1.75 ± 1.28 vs. 1.88 ± 0.69; p = 0.09) did not differ significantly between NC-FET vs HRC-FET. Significantly higher live births took place in NC-FET vs. HRC-FET (87/173 = 50.3%vs.204/507 = 40.2%;p = 0.026). No significant difference was found in pregnancy rate (66.5% vs. 58%; p = 0.058) or in the pregnancy loss rate (24.3%vs30.6%; p = 0.23). The odds ratio for live-births adjusted for relevant variables was 1.48 (1.03-2.13) in NC-FET compared to HRC-FET.

CONCLUSIONS

NC-FET is a superior method of endometrial preparation compared to HRC-FET in eumenorrhoeic women since it has a shorter estrogenic phase, reduces patient visits to the hospital and improves live birth rates. Future adequately powered studies should look at antenatal and perinatal outcomes, patient satisfaction rates and cost-effectiveness in the two endometrial preparation regimes.

Effects of different cycle regimens for frozen embryo transfer on perinatal outcomes of singletons

STUDY QUESTION

Does the endometrial preparation protocol for frozen embryo transfer (FET) have an impact on perinatal outcomes?

SUMMARY ANSWER

Singleton newborns from conceptions after an artificial FET cycle had a higher risk of being large for gestational age (LGA).

WHAT IS KNOWN ALREADY

Most previous studies have concentrated on the clinical pregnancy, miscarriage and live birth rates of different endometrial preparation protocols for FET. However, the impacts of these cycle regimens on perinatal outcomes including birthweight, gestational age (GA) and related outcomes require more investigation.

STUDY DESIGN, SIZE, DURATION

We retrospectively analysed all singletons conceived by women who underwent non-donor FET cycles between July 2014 and July 2017. The propensity score matching (PSM) method using nearest neighbour matching at a proportion of 1:1 was established to adjust for factors that influence the probability of receiving different FET cycle regimens. The main outcomes of the study included birthweight and its related outcomes, Z-score, low birthweight (LBW, <2500 g), small for gestational age (SGA, ≤10th percentile of referential birthweight), LGA (≥90th percentile of referential birthweight) and macrosomia (birthweight >4000 g). The study outcomes also included GA at birth, preterm delivery (<37 weeks), very preterm delivery (<32 weeks), very low birthweight (VLBW, <1500 g), term LBW (at 37 weeks of gestation or greater) and preterm LBW (at <37 weeks of gestation).

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 9267 cycles with live-born singletons were included in the analysis in our centre between July 2014 and July 2017. Of these, 2224, 4299 and 2744 live-born singletons were conceived by natural cycle FET, stimulated cycle FET and artificial cycle FET, respectively. After PSM, 1947 cycles of natural cycle FET versus stimulated cycle FET, 1682 cycles of stimulated cycle FET versus artificial cycle FET and 2333 cycles of natural cycle FET versus artificial cycle FET were included in the analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

A higher mean birthweight and Z-score were observed in the artificial cycle FET group than in the stimulated cycle FET group (P = 0.005; P = 0.004, respectively). Singleton newborns conceived after artificial cycle FET were more likely to be LGA than those born after natural cycle FET or stimulated cycle FET (19.92% versus 16.94% and 19.29% versus 16.12%, respectively). The adjusted ORs (95% CIs) were 1.25 (1.05, 1.49) for artificial cycle FET compared with natural cycle FET (P = 0.014) and 1.26 (1.08, 1.46) for artificial cycle FET compared with stimulated cycle FET (P = 0.003). Newborns conceived after stimulated cycle FET had a lower mean GA at birth and a lower mean birthweight than those born after natural cycle FET or artificial cycle FET. The stimulated cycle FET group had lower adjusted odds of being macrosomia than the natural cycle FET group. No significant differences between natural cycle FET and stimulated cycle FET were found for any of the other outcomes.

LIMITATIONS, REASONS FOR CAUTION

This study had the disadvantage of being retrospective, and some cases were excluded due to missing data. The original allocation process was not randomized, which may have introduced bias. We have chosen not to account for multiple comparisons in our statistical analysis.

WIDER IMPLICATIONS OF THE FINDINGS

LGA can have long-term consequences in terms of risk for disease, which means that the influences of artificial cycle FET are of clinical significance and deserve more attention. Furthermore, these findings are critical for clinicians to be able to make an informed decision when choosing an endometrial preparation method.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from the National Natural Science Foundation of China (NSFC) (31770989 to Y.W.) and the Shanghai Ninth People's Hospital Foundation of China (JYLJ030 to Y.W.). None of the authors have any conflicts of interest to declare.

Pregnancy Outcomes After Different Cycle Regimens for Frozen-Thawed Embryo Transfer: A Retrospective Study Using Propensity Score Matching

Background: Nowadays, the choice of frozen embryo transfer (FET) regimens is mainly guided by personal convenience. Clinicians prefer the predictability and reliability of artificial cycle (AC) FET and have extended its usage to general in vitro fertilization population. More recent primary studies are beginning to challenge the comparability of AC-FET and suggest reduced clinical pregnancy rate and live birth rate (LBR) compared with those in modified natural cycle (mNC) FET (ovulation triggered by human chorionic gonadotrophin) and stimulated cycle (SC) FET.

Objective: To assess the pregnancy outcomes within matched mNC-FET, SC-FET, and AC-FET cycles by using propensity score matching (PSM) in a larger cohort.

Methods: A total of 16,946 women who underwent their first autologous FET cycle between July 2014 and July 2017 were evaluated. PSM, using the nearest neighbor matching, were established to adjust the baseline features within the three protocols in proportion of 1:1 (mNC-FET vs. SC-FET, mNC-FET vs. AC-FET, SC-FET vs. AC-FET). Furthermore, there were 3,567, 2,917, and 3,964 cycles compared between matched mNC-FET and SC-FET, mNC-FET and AC-FET, and SC-FET and AC-FET after the PSM, respectively.

Results: LBR was significant lower in the AC-FET group than that in the mNC-FET (40.0 vs. 43.3%) and SC-FET groups (40.9 vs. 46.5%). The adjusted odds ratios (95% CIs) were 1.11 (1.00, 1.24) for mNC/AC (P = 0.044) and 0.84 (0.76, 0.92) for AC/SC (P < 0.001), which indicated that the AC-FET group was associated with lowest LBR. The LBR was comparable between matched mNC-FET and SC-FET after adjusting for endometrial thickness. Moreover, a lower clinical pregnancy rate and a higher risk of early pregnancy loss were discovered in AC-FET cycles compared with those in SC-FET.

Conclusion: In view of our data, AC used for scheduling FET was associated with lower LBR compared with SC and modified natural cycle. This interpretation requires future verification from well-designed prospective multicenter randomized clinical trials, although the comparisons in our study were conducted in the homogenous population after the PSM.

Preimplantation Genetic Testing: Where We Are Today

BACKGROUND

Preimplantation genetic testing (PGT) is widely used today in in-vitro fertilization (IVF) centers over the world for selecting euploid embryos for transfer and to improve clinical outcomes in terms of embryo implantation, clinical pregnancy, and live birth rates.

METHODS

We report the current knowledge concerning these procedures and the results from different clinical indications in which PGT is commonly applied.

RESULTS

This paper illustrates different molecular techniques used for this purpose and the clinical significance of the different oocyte and embryo stage (polar bodies, cleavage embryo, and blastocyst) at which it is possible to perform sampling biopsies for PGT. Finally, genetic origin and clinical significance of embryo mosaicism are illustrated.

CONCLUSIONS

The preimplantation genetic testing is a valid technique to evaluated embryo euploidy and mosaicism before transfer.