Single Euploid Frozen Embryo Transfer Research Articles

P-711 Female age at embryo creation and embryo transfer do not impact the ongoing pregnancy rates in single euploid frozen embryo transfers

Abstract Study question Which factors influence the ongoing pregnancy rate in single euploid frozen embryo transfer (seFET) cycles? Summary answer Ongoing pregnancy rates in seFET cycles are significantly influenced by parity, BMI, embryo quality, trophectoderm biopsy day and endometrial preparation, but not by female age. What is known already The probability of a pregnancy is influenced by several factors and female age is the major determinant as the ovarian reserve decreases and embryo aneuploidy increases with age. Preimplantation genetic testing for aneuploidy and embryo selection was considered to mitigate the effect of female age on ART treatment outcomes by selecting euploid embryo(s) for embryo transfer (ET). Previously published data point to a decline in pregnancy rates with increased maternal age even when a euploid embryo is transferred. However, other factors besides embryo ploidy might play a role in the chance of achieving an ongoing pregnancy. Study design, size, duration Retrospective study, including 1923 women who underwent a seFET between 04/2017 and 08/2023. Patients’ (age at oocyte-pick-up and seFET, BMI, parity, endometrial preparation type) and embryo characteristics (Day of biopsy, embryo quality (EQ)) were considered for the analysis. Ongoing pregnancy was defined as viable pregnancy beyond 12 weeks of gestation. Participants/materials, setting, methods Women, undergoing a seFET either in a true natural cycle (NC) t or in a hormonal replacement cycle (HRT). Only cycles with embryos being biopsied on day 5 or day 6 and a known outcome of the cycle were included. Main results and the role of chance There were 990 (51.48%) ongoing pregnancies among 1923 included transfers. The ongoing pregnancy rates were 51.8%, 47.4%, 52.3% and 52.8% for women aged ≤35, >35 to ≤ 37, >37 to ≤ 40, and >40 years-old at seFET, respectively. Cochrane Armitage test did not show a significant trend for decreasing pregnancy rates with increasing female age at OPU (P = 0.679) or at transfer (P = 0.609). Multivariable regression analyses showed primiparous, and multiparous women were more likely to have an ongoing pregnancy compared to nulliparous women (OR: 2.96, 95%CI:2.22-3.94 and 2.73, 95%CI:2.10-3.55, respectively, P < 0.001 for both) and those who had a natural endometrial preparation (OR: 1.53, 95%CI: 1.24-1.88, P < 0.001). Transfers with good quality embryo had higher ongoing pregnancy rates compared to those who had a fair quality embryo (OR: 2.0, 95%CI: 1.37-2.91, P < 0.001). Being overweight or obese at the time of transfer were associated with lower ongoing pregnancy rates compared to normal weight (OR: 0.71, 95%CI: 0.56-0.89, and 0.68, 95%CI: 0.52-0.88, respectively, P = 0.003 for both). Age categories at the time of transfer did not show a significant effect on ongoing pregnancy rates in multivariable analyses (P > 0.05 for all) and there was no significant interaction between age at OPU and embryo quality categories either (P = 0.881 and 0.601). Limitations, reasons for caution The retrospective design of the study is a limitation. Wider implications of the findings This analysis did not confirm the otherwise reported negative impact of female age on the outcome of seFET cycles. Outcomes are significantly influenced by BMI, parity, EQ-related factors as well as the endometrial preparation. As BMI and endometrial preparation can be influenced, the adequate choice might improve seFET outcomes. Trial registration number not applicable

P-407 Exploring the effectiveness of tailoring estradiol supplementation duration to mimic the natural cycle length in artificial endometrial preparation for frozen embryo transfer cycles

Abstract Study question Is an estrogen supplementation duration similar in length to the follicular phase of a natural cycle associated with a better clinical pregnancy rate? Summary answer An estradiol supplementation duration, which is proportional to the natural follicular phase length, results in significantly better outcomes compared to shorter exposure durations What is known already The last decade witnessed a major increase in the use of single euploid frozen embryos. Artificial endometrial preparation (AEP) has proven to be effective to prepare the endometrium for implantation. However, several features of AEP need to be clarified mainly the duration of estrogen supplementation and until now no study took into consideration the difference between exogenous estrogen supplementation and the actual length of the follicular phase of each patient during AEP. Furthermore, most of the studies focused on upper limit of estrogen exposure while few considered the lower limit. Unfortunately, the results on pregnancy rates were mixed. Study design, size, duration 663 single euploid frozen embryo transfer cycles were included. Patients underwent vaginal ultrasound and hormonal blood measurement (Estradiol, Progesterone) on day 2 of their cycle. Estradiol valerate (4 mg the first 2 days then 6 mg daily, Orally) was started on the same day and another control was done around day 10. When triple lining pattern of the endometrium was seen, vaginal progesterone was initiated (800 mg daily) and SET was done after 120 hours. Participants/materials, setting, methods Patients with reported regular menstrual cycle (25-35 days) were included and the difference between estrogen supplementation and the actual follicular phase was calculated for each patient. Patients were sorted into 2 groups as follows: 231 women with normal interval (±2 days of follicular phase length), and 432 women with short interval (-3 days or shorter). Only the first single euploid embryo transfer cycles were analyzed for these patients. Main results and the role of chance Whereas patients had similar characteristics in both groups, the corresponding clinical pregnancy rates in normal and short supplementation groups were 69.3% (160/231) and 64% (277/432), respectively. After balancing the groups for BMI, embryo quality and endometrial thickness with inverse treatment probability weighting, those who received estradiol supplementation proportional to their natural follicular phase length had significantly higher clinical pregnancy rates compared to those who received it for shorter durations (adjusted OR: 1.48, 95% CI: 1.16 – 1.89, P = 0.002). Serum estradiol levels were available for 523 cycles, the clinical pregnancy rate in those within the 1st quartile (<155pmol/L), 2nd to 3rd quartile (155 to 275pmol/L) and 4th quartile (>275pmol/L) were 70%, 64.7% and 63%. After adjusting for BMI and embryo quality, higher (>275pmol/L) (adjusted OR: 0.84, 95% CI: 0.53-1.32, P = 0.442) and lower(<155pmol/L) (adjusted OR: 1.37, 95% CI: 0.85-2.22, P = 0.202) estradiol levels were not significantly associated with clinical pregnancy. Limitations, reasons for caution The present study could not address the influence of very long estrogen supplementation on clinical pregnancy rate due to limited samples. Further prospective studies, including larger populations, are needed to confirm our findings Wider implications of the findings Our data indicate that mimicking individually the natural cycle regarding estrogen supplementation duration in AEP for single euploid embryo transfer cycles can produce significant improvement in clinical pregnancy rates. Trial registration number not applicable

Ongoing pregnancy rates in single euploid frozen embryo transfers remain unaffected by female age: a retrospective study

Research questionIs female age a significant factor in the likelihood of an ongoing pregnancy in single euploid frozen embryo transfers (seFET)? DesignRetrospective study of 1923 seFET cycles from 1464 women, either in a natural cycle (NC) or a hormonal replacement therapy cycle. Outcome was the ongoing pregnancy rate (OPR). ResultsThere were 990 (51.48%) ongoing pregnancies among 1923 included transfers. The OPR were 51.4%, 49.1%, 53.3% and 52.3% for women aged ≤35, >35 to ≤37, >37 to ≤40, and >40 years-old at OPU without a significant trend for decreasing OPRs (P=0.679). No significant differences between the groups (OPR vs. no pregnancy or miscarriage) were seen for female age at transfer (P=0.609) or at OPU (P=0.816). Women who received good quality embryos (P<0.001), with lower BMI (P<0.001), at least one previous pregnancy (P<0.001) and a NC (P<0.001) had significantly higher OPR. Multivariable regression (adjusted for BMI, embryo quality, endometrial preparation) analysis did not show a significant effect of female age at OPU on achieving an OPR. Compared to women ≤35-year-old, none of the age groups had significantly higher or lower pregnancy rates. A multinomial regression analysis showed that both, miscarriage and no pregnancy vs. ongoing pregnancy was associated with BMI, embryo quality and endometrial preparation. Again, female age had no significant associations with either outcome. Conclusion(s)The herein presented data demonstrate no substantial impact of female age on its own on the OPR in seFET cycles, but a significant impact of embryo quality, BMI, previous parity and a NC protocol.

Live birth after single euploid frozen embryo transfer in a 39-year-old woman with high-grade mosaic Turner syndrome

Objective To describe the reproductive and obstetric outcomes of an intracytoplasmic sperm injection cycle with preimplantation genetic testing for aneuploidy in an advanced reproductive-age woman with high-grade mosaic Turner syndrome. Methods Case report of a 39-year-old woman diagnosed with mosaic Turner Syndrome 45,X[90]/46,XX[10] karyotype who underwent in vitro fertilization treatment with blastocyst trophectoderm biopsy for preimplantation genetic testing using next-generation sequencing. Result(s) Two of the four blastocysts biopsied were euploid. The patient achieved ongoing pregnancy after the first single euploid frozen embryo transfer, followed by the birth of a healthy child. Conclusion Autologous intracytoplasmic sperm injection cycles can be considered in a select group of advanced reproductive-age women diagnosed with high-grade mosaic Turner syndrome.

P-501 Live birth rates (LBR) are not influenced by a change in embryo quality imposed by embryo cryopreservation and thawing in single euploid frozen embryo transfers.

Abstract Study question Is a change of embryo quality through vitrification and thawing associated with a reduced LBR when a single euploid frozen embryo transfer is performed? Summary answer Live birth rates are not influenced by a change in embryo quality through embryo cryopreservation and thawing in single euploid frozen embryo transfer. What is known already Embryo aneuploidy is the most significant single factor and accounts for about 50% of implantation failure and miscarriage in human reproduction. Preimplantation genetic test for aneuploidy (PGT-A) presents a mean to identify euploid embryos, thereby improving pregnancy rates and reducing early pregnancy losses. However, after PGT-A on trophectoderm cells at blastocyst stage, embryos have to be cryopreserved and warmed later for the embryo transfer procedure. Embryo quality is known to impact implantation and ongoing pregnancy rates, therefore, the aim of this analysis was to evaluate the impact of a change in embryo quality between pre-vitrification and post-thaw on the outcome. Study design, size, duration This retrospective observational study included a total of 611 pregnant patients after frozen-thawed euploid single embryo transfer (FET) at a tertiary IVF centre between April 2017 and December 2020. All embryos transferred were cryopreserved after trophectoderm biopsy for PGT-A, performed either on day 5 or day 6. Each patient was only included once into the analysis. Endometrial preparation for FET was performed either in a natural cycle (NC) or as a hormonal replacement cycle (HRT). Participants/materials, setting, methods Patients with infertility, undergoing ovarian stimulation and FET in either a HRT or a NC as endometrial preparation approach, and who achieved a pregnancy, were included. Embryos were morphologically graded pre-vitrification and post-thaw based on inner cell mass and trophectoderm morphology on the day of cryopreservation. Four groups were initially established (top, good, fair, poor), hence for the analysis, fair and poor qualities were combined. Main results and the role of chance A total of 591 patient were analysed after exclusion of 20 patients due to the occurrence of late miscarriage and ectopic pregnancy. Patients’ characteristics are as follows (mean±SD (min-max)): age 33.87±5.55(20-47) years; AMH 3.20±3.28ng/mL(0.01-35.72); BMI(body mass index) 26.61±4.86kg/m2(14.84-40.31) and AFC 14.00±7.33(1-35). The changes in the embryo quality pre-vitrification and post-thaw were categorized in “no change”, “improved” or “degraded”. All groups were compared to top-quality-no change group. A binary logistic analysis evaluated the following groups regarding their combined impact on LB: top quality-degraded (odds ratio (OR)0.702; 95% confidence interval (CI)0.302-1.635, p = 0.413); good quality-no change (OR 1.022; CI:0.457-2.287; p = 0.958); good quality-degraded (OR 0.787; CI:0.330-1.880; P = 0.590); good quality-improved (OR 0.301; 0.056-1.628; P = 0.163); fair+poor quality-no change(OR 0.521; 0.203-1.340; P = 0.176); fair+poor quality-degraded (OR 0.283; 0.056-1.438; P = 0.128) and fair+poor quality-improved (OR 1.917; 0.431-8.534; P = 0.393). No impact on the probability of LB was seen in any combined group of change in embryo quality with its pre-grades. Furthermore, no association was found for age, BMI, AMH, pre-vitrification and post-thaw quality. Embryos biopsied on day 6 instead day 5 had a decreased chance of a LB (OR 0.516; 0.305-0.875, p = 0.014). Further on, NC was associated with significantly higher chance of LB compared to HRT cycle (OR 2.629; 1.606-4.305, p = &amp;lt;0.001). Limitations, reasons for caution Limitation is the retrospective design of the study and the grading of the embryos, which might be subjective and bearing interobserver variability. Wider implications of the findings Whereas a change in the embryo quality does not impact the chance of LB after single euploid FET, a NC approach increases the odds for LB. This fact should be considered for a personalized treatment approach and in the choice of the endometrial preparation protocol. Trial registration number not applicable

O-194 Blastulation timing in embryos is influenced by ploidy and is a predictor of transfer outcome

Abstract Study question Is there an association of the timing of blastulation (TE biopsy day) on embryo ploidy and pregnancy outcome after frozen embryo transfer? Summary answer Blastocysts expanded on day 5 are more likely to be euploid and result in an ongoing pregnancy after single euploid frozen embryo transfer (FET). What is known already Embryo selection for ET is commonly based on static morphological parameters for patients undergoing in vitro fertilization (IVF). Embryo quality on the day of biopsy in combination with preimplantation genetic testing (PGT) are considered important predictors for successful implantation. At present, coherent data regarding any association between the timing of blastulation with embryo ploidy and pregnancy outcomes following single FET are lacking. The aim of our study was to investigate the correlation of the culturing method and blastulation day (day 5/6/7) with embryo ploidy and outcomes of matched d5 vs d6 vs d7 FET cycles. Study design, size, duration This retrospective cohort study was performed at the CReATe Fertility Centre and its Reproductive Genetics Laboratory, between January 2019-December 2022. 29660 blastocysts from 5302 cycles (3645 patients) were analyzed using high resolution NGS PGT-A (10Mb resolution for copy number variations and 30%-70% for mosaicism). Pregnancy outcome data from 3942 single-FETs were analyzed. Average age of ovum provider was 32.9±5.8 and sperm provider 39.1±6.4. Clinical, laboratory and demographic data were obtained for statistical analysis. Participants/materials, setting, methods Embryos were allocated into four groups based on static morphological grading before biopsy on either d5 (n = 8312), d6 (n = 19183) or d7 (n = 2165): Good (&amp;gt;1/2BB), n = 5648, Average (1BB, 2BB), n = 10492, Poor (&amp;lt;1/2 BB) n = 12219 and Early blast, n = 1301. Embryo ploidy in each group and pregnancy outcomes from single euploid FET were compared between matched cycles of day 5 biopsy to days 6 and 7. Main results and the role of chance PGT-A analysis of 29660 embryos showed 53.1% were euploid, 33.9% were aneuploid and 13.0% were mosaic. There were significantly higher proportion of euploid embryos among those biopsied on d5 compared to d6 and d7 with average morphology grade (p = 0 O.R.=1.35979; p = 0.008098 O.R.=1.34442), poor (p = 0 O.R.=1.76481; p = 0 O.R.=2.73903) and early grades (p = 0 O.R.=2.71891; p = 0 O.R.=2.74271), but not among embryos with good grade (p = 0.244399 O.R.=1.07276; p = 0.182084 O.R.=1.38189). Ongoing pregnancy rates were significantly higher for d5 vs d6 biopsied embryos, for all morphology grade groups: good (p = 0.030036 O.R.=1.26598), average (p = 0 O.R.=1.80782), poor (p = 0.000303 O.R.=1.89235) and early blasts (p = 0.049501 O.R.=3.30556). D5 blasts had higher ongoing pregnancy rates compared to d7 among average and poor morphology grade as well as early blast (p = 0.000419 O.R.=8.93182, p = 0.000036 O.R.=7.29464, p = 0.010034, respectively), except among good grade embryos (p = 0.885598 O.R.=0.9028). Continuous culture of embryos in Embryoscope™ versus conventional incubator did not influence the ploidy (n = 24321; n = 4756, respectively) or the pregnancy outcome after FET (n = 3134; n = 752, respectively) while comparing between each day of biopsy. Limitations, reasons for caution Although this is the largest sample size study to investigate the association of blastulation with ploidy and pregnancy outcomes, the sample size for d7 embryos is relatively low and results should be confirmed in a bigger study. Wider implications of the findings Prioritization of euploid embryos for transfer should consider the timing to blastulation and embryos biopsied on d5 should be considered before those biopsied on d6 or d7. This data has potential to shed light on the impact of normal chromosomal content on preimplantation embryo development. Trial registration number not applicable

P-311 Embryo morphological grade and day of vitrification can impact the outcome of a single euploid frozen embryo transfer (FET)

Abstract Study question How does the embryo morphological grade and day of vitrification affect FET outcomes from in vitro fertilization cycles utilizing preimplantation genetic testing for aneuploidy (PGT-A)? Summary answer The morphological grade of a transferred embryo affects FET outcomes in age groups differently, and Day-5 embryos have significantly better pregnancy outcomes than Day-6 embryos. What is known already The use of PGT-A has shown to increase implantation rates, lower miscarriage rates and promote counseling for a single embryo transfer. Although euploid embryos are the priority for transfer, it is important to examine embryo characteristics that may influence these outcomes within these euploid embryos to maximize the outcome for each FET. Study design, size, duration In this retrospective study, 1,554 FETs transferring one euploid Day-5 or Day-6 embryo between January 2020 and October 2022 were evaluated, with the exclusion of donor oocyte, donor embryo, gestational carrier and Day-7 embryo transfer cycles. The inner cell mass and trophectoderm were each categorized as good (G), fair (F) or poor (P) respectively at the time of embryo cryopreservation. A total of 282 GG, 1,053 FG, and 209 FF embryos were transferred. Participants/materials, setting, methods Embryo grade categories were used to compare Day-5 versus Day-6 transfer outcomes and by age groups. Separating groups as &amp;lt; 34, 34-37, and ≥38 eliminated age as a significant factor. Primary outcomes included rates of positive chemical pregnancy (CP), biochemical loss (BL), clinical uterine gestation (CIG), and fetal cardiac activity (FCA). Independent t-tests compared age, and aggregate data was analyzed by proportional z-tests. A p-value &amp;lt;0.05 was defined as statistically significant with a 95% confidence interval. Main results and the role of chance Age and BL were not significant between transfer days or age groups. Day-5 had higher CP (GG: 84% vs 65%, p &amp;lt; 0.001; FG: 75% vs 59%, p = 0.006; FF: 63% vs 44%, p = 0.019), CIG (GG: 73% vs 57%, p = 0.006; FG: 64% vs 48%, p &amp;lt; 0.001; FF: 55% vs 34%, p = 0.007), and FCA (GG: 66% vs 52%, p = 0.022, FG: 60% vs 40%, p &amp;lt; 0.001, FF: 55% vs 30%, p &amp;lt; 0.001). For patients &amp;lt;34, GG had higher CP compared to FG and FF (74% vs 64%, p = 0.017; 74% vs 46%, p &amp;lt; 0.001), CIG (66% vs 55%s, p = 0.011; 66% vs 38%, p &amp;lt; 0.001) and FCA (61% vs 50%, p = 0.012; 61% vs 38%, p = 0.001). FG had higher CP (64% vs 46%, p = 0.007) and CIG (55% vs 38%, p = 0.008) compared to FF. For patients 34-37, GG and FG had higher CP (78% vs 53, p &amp;lt; 0.001; 70% vs 53%, p = 0.004), CIG (66% vs 42%, p = 0.002; 56% vs 42%, p = 0.029), and FCA (58% vs 35%, p = 0.002; 50% vs 35%, p = 0.011) compared to FF. When compared to FF in patients ≥38, GG and FG had increased CP (79% vs 47%, p &amp;lt; 0.001; 64% vs 47%, p = 0.012) and CIG (65% vs 36%, p = 0.004; 53% vs 36%, p = 0.010). Only GG had higher FCA (56% vs 36%, p = 0.049). Limitations, reasons for caution Even with the exclusion criteria, the retrospective nature of the study may be viewed as a limitation, so the significance of the results should be evaluated further. Wider implications of the findings Based on these results, this study demonstrates the need to compare the characteristics of euploid embryos before selection to maximize the chance of pregnancy. Embryos vitrified on Day-5 or categorized as GG, especially in patients &amp;lt;34, or FG should be prioritized over Day-6 or FF embryos. Trial registration number not applicable

A balancing act: sex selection after pre-implantation genetic testing for aneuploidy for first versus second baby.

How often do patients undergoing frozen embryo transfer (FET) after preimplantation genetic testing for aneuploidy (PGT-A) choose to select for sex and do sex selection rates differ before and after successful delivery of a first baby? When a choice was available between male and female embryos, patients selected the sex more frequently when trying to conceive the second child (62%) as compared to the first child (32.4%) and most commonly selected for the opposite sex of the first child. Sex selection is widely available in US fertility clinics. However, the rate of sex selection for patients undergoing FET after PGT-A is unknown. This is a retrospective cohort study of 585 patients that took place between January 2013 and February 2021. The study took place at a single, urban academic fertility center in the USA. Patients were included if they had a live birth after single euploid FET and returned for at least one subsequent euploid FET. The primary outcomes were the rates of sex selection for first versus second baby. Secondary outcomes were rate of selection for same versus opposite sex as first live birth and overall rate of selection for males versus females. Five hundred and eighty-five patients underwent a total of 1560 single euploid FETs resulting in either one or two live births. A choice between male and female euploid embryos was available for 919 FETs (first child: 67.5% (519/769) versus second child: 50.6% (400/791), P < 0.01). When a choice was available, patients selected the sex more frequently when trying to conceive the second child (first child: 32.4% (168/519) versus second child: 62.0% (248/400), P < 0.01). When sex was selected after first live birth, the opposite sex of the first child was selected 81.8% (203/248 FETs) of the time. Of transfers that involved sex selection, rates of male and female selection were similar for the first child, but selection for females was greater for the second child (first child: 51.2% (86/168) male versus 48.9% (82/168) female, second child: 41.1% (102/248) male versus 58.9% (146/248) female, P < 0.04). The study was performed at one urban academic medical center in the Northeastern US, which may limit generalizability to other settings where PGT-A may be performed less frequently, or sex selection may be limited or not permitted. In addition, we could not reliably account for whether patients or their partners had prior children and if so, of what sex. Patients undergoing PGT-A with both male and female euploid embryos were more likely to select for sex when attempting a second child and usually selected for the opposite sex of their first child. These findings highlight the potential for family balancing for patients who undergo PGT-A in settings where sex selection is permitted. This study received no funding. The authors have no conflicts of interest to declare. N/A.

Recent clomiphene citrate exposure does not impact subsequent clinical outcomes in single euploid frozen embryo transfer cycles

Do infertile couples who recently utilized clomiphene citrate (CC) for ovulation induction or ovarian stimulation (<90 days previously) followed by a single euploid embryo transfer (SEET) have lower implantation potential compared with patients who were not exposed to CC within 90 days before embryo transfer (ET)? There does not appear to be an association between recent CC exposure and lower implantation potential in patients who undergo a frozen embryo transfer (FET) of euploid embryos. Clomiphene has been found to be associated with lower pregnancy rates when compared against other ovarian stimulation medications. The majority of published research about the effects of CC on implantation potential suggest an anti-estrogenic effect on the endometrium. Quality evidence and information about utilization of CC and its effect on implantation potential after euploid ETs is lacking in the literature. A retrospective cohort study with propensity score matching was carried out. We included all patients that underwent an autologous SEET from September 2016 to September 2022 at a single academic-private ART center. The study group included patients that had utilized CC during either ovulation induction cycles and/or controlled ovarian stimulation at least 90 days before FET. A propensity score-matched control group of patients that were unexposed to CC within 90 days prior to SEET was used for comparisons. The primary outcome was positive pregnancy test (defined as a positive serum β-hCG measured 9 days after ET), with other outcomes including clinical pregnancy, ongoing pregnancy, biochemical pregnancy loss, and clinical pregnancy loss rates per SEET. Multivariate regression analyses fitted with generalized estimating equations were utilized to analyze if there was an association between CC utilization and IVF outcomes. Furthermore, the study evaluated the cumulative effect of CC and endometrial receptivity in vivo and subsequent IVF outcomes. A total of 593 patients with utilization of CC in <90 days before ET were compared with 1779 matched controls. Positive pregnancy test rates were comparable among the control group and the CC exposed groups, respectively (74.3% versus 75.7%, P = 0.79), as were clinical pregnancy (64.0% versus 65.0%, P = 0.60), ongoing pregnancy (51.8% versus 53.2%, P = 0.74), biochemical pregnancy loss (15.7% versus 14.03%, P = 0.45), and clinical pregnancy loss rates were also comparable among cohorts (17.1% versus 18.1%, P = 0.71). No association was found between utilization of clomiphene and lower implantation rates (adjusted odds ratio 0.95, 95% CI 0.76-1.18). Also, no differences were observed in sub-analyses based on multiple CC utilization periods. Finally, no association was found between the number of consecutive cumulative clomiphene cycles and sub-optimal IVF outcomes. The study has inherent bias that originated from its retrospective design. Serum levels of CC were not measured and sample size for the sub-analyses was small. There does not appear to be an association between recent CC exposure and lower implantation potential in patients who undergo a FET of euploid embryos. This finding remains consistent, even in patients who undergo multiple, consecutive clomiphene cycles prior to ET. There were no long-term effects of CC on endometrial development and clinical characteristics examined in this study. Patients that utilized CC medication prior to a SEET cycle for either ovarian stimulation or ovulation induction, can be assured that there is no evidence of a residual effect of recent CC administration that could jeopardize their pregnancy probability. No funding was received for the realization of this study. A.C. is advisor and/or board member of Sema4 (stakeholder in data) and Progyny. The other authors have no conflicts of interest to declare. N/A.

Effect of Timing by Endometrial Receptivity Testing vs Standard Timing of Frozen Embryo Transfer on Live Birth in Patients Undergoing In Vitro Fertilization

Endometrial receptivity testing is purported to improve live birth following frozen embryo transfer by identifying the optimal embryo transfer time for an individual patient; however, data are conflicting. To compare live birth from single euploid frozen embryo transfer according to endometrial receptivity testing vs standardized timing. Double-blind, randomized clinical trial at 30 sites within a multicenter private fertility practice in the Eastern US. Enrollment was from May 2018 to September 2020; follow-up concluded in August 2021. Participants underwent in vitro fertilization, preimplantation genetic testing for aneuploidy, endometrial receptivity testing, and frozen embryo transfer. Those with euploid blastocyst(s) and an informative receptivity result were randomized. Exclusion criteria included recurrent pregnancy loss, recurrent implantation failure, surgically aspirated sperm, donor egg(s), and unmitigated anatomic uterine cavity defects. The intervention group (n = 381) underwent receptivity-timed frozen embryo transfer, with adjusted duration of progesterone exposure prior to transfer, if indicated by receptivity testing. The control group (n = 386) underwent transfer at standard timing, regardless of receptivity test results. The primary outcome was live birth. There were 3 secondary outcomes, including biochemical pregnancy and clinical pregnancy. Among 767 participants who were randomized (mean age, 35 years), 755 (98%) completed the trial. All randomized participants were analyzed. The primary outcome of live birth occurred in 58.5% of transfers (223 of 381) in the intervention group vs 61.9% of transfers (239 of 386) in the control group (difference, -3.4% [95% CI, -10.3% to 3.5%]; rate ratio [RR], 0.95 [95% CI, 0.79 to 1.13]; P = .38). There were no significant differences in the intervention vs the control group for the prespecified secondary outcomes, including biochemical pregnancy rate (77.2% vs 79.5%, respectively; difference, -2.3% [95% CI, -8.2% to 3.5%]; RR, 0.97 [95% CI, 0.83 to 1.14]; P = .48) and clinical pregnancy rate (68.8% vs 72.8%, respectively; difference, -4.0% [95% CI, -10.4% to 2.4%]; RR, 0.94 [95% CI, 0.80 to 1.12]; P = .25). There were no reported adverse events. Among patients for whom in vitro fertilization yielded a euploid blastocyst, the use of receptivity testing to guide the timing of frozen embryo transfer, compared with standard timing for transfer, did not significantly improve the rate of live birth. The findings do not support routine use of receptivity testing to guide the timing of embryo transfer during in vitro fertilization. ClinicalTrials.gov Identifier: NCT03558399.

P-589 Natural endometrial preparation for single euploid frozen embryo transfer increases the likelihood of live birth in obese patients

Abstract Study question Does a natural endometrial preparation for single euploid frozen embryo transfer increase the odds of live birth (LB) in obese patients? Summary answer Compared to an artificial approach, a natural endometrial preparation for single euploid frozen embryo transfer improves the odds of LB in obese patients. What is known already Several protocols to prepare the endometrium for frozen embryo transfer have been described with comparable clinical outcomes, and no individual protocol has been demonstrated to be superior. Likewise, no specific patient group has been defined that can substantially benefit from a natural endometrial preparation. Despite obesity being linked to adverse clinical outcomes, observational studies and clinical trials have traditionally included participants with normal weight when comparing protocols, resulting in obese patients being underrepresented in clinical research. Therefore, studies focusing on endometrial preparation protocols for frozen embryo transfer that include obese patients are required. Study design, size, duration This study involved the analysis of a retrospective dataset including 975 single euploid frozen embryo transfer cycles performed at two tertiary referral centers between March 2017 and November 2019. The primary outcome was LB after natural and artificial endometrial preparation. Participants were stratified according to the World Health Organization Body mass index (BMI) classification into three groups (G): G1: Normal-weight ≤24.9 (n = 390), G2: Overweight 25 to 29.9 (n = 332), and G3: Obese ≥30 (n = 253). Participants/materials, setting, methods Cycles included infertility patients attempting a single euploid frozen blastocyst transfer under natural (n = 324) or artificial (n = 651) endometrial preparation. PGT-A was performed after trophectoderm biopsy using Next-Generation Sequencing. Spontaneous LH rise confirmed ovulation for natural endometrial preparation, and embryo transfer occurred five days after initial progesterone elevation. Hormones were measured from blood samples. For artificial preparation, embryo transfer was performed after oral estradiol and 120-hour vaginal progesterone exposure. All participants received luteal phase support. Main results and the role of chance Within each BMI group, no statistically significant differences in age were observed in patients between a natural and artificial endometrial preparation: G1 (33.5±5.1 vs. 32.7±5.2 years; p = 0.13), G2 (34.5±4.9 vs. 33.9±5.8 years; p = 0.39), and G3 (35.6±4.9 vs. 34.3±5.6 years; p = 0.1). Similarly, no statistically significant differences were observed regarding implantation rates: G1 (60% vs 57.1%; p = 0.57), G2 (54.8% vs 55.7%; p = 0.88), and G3 (64.3% vs 51.4%; p = 0.07). LB rates remained constant across all BMI groups when a natural preparation was conducted: G1 [56.66% (n = 85/150)], G2 [49.03% (n = 51/104)], and G3 [58.57% (n = 41/70)]. We observed a decrease in LB rates in G3 when an artificial endometrial preparation was performed: G1 [47.5% (n = 114/240)], G2 [44.73% (n = 102/228)], and G3 [34.42% (n = 63/183)]. The positive impact of a natural preparation on LB rates was more significant in G3, showing a 24% difference of effect between the natural and artificial endometrial preparations. Univariate logistic regression analysis showed a statistically significant difference in the primary outcome (LB) when a natural endometrial preparation was conducted in G3 (OR 2.69, 95% CI 1.53-4.74; p = 0.001), with no differences found in G1 (OR 1.45, 95% CI 0.96-2.18; p = 0.08) and G2 (OR 1.19, 95% CI 0.75-1.89; p = 0.73). Limitations, reasons for caution This study could be subject to bias due to its retrospective nature. Sperm quality was not considered for the present study. Wider implications of the findings Obese women appear to be the patient group that can obtain benefit from a natural endometrial preparation for frozen embryo transfer by increasing the odds of LB. Future prospective studies should confirm this hypothesis. A natural approach might be unfeasible in a subgroup of obese patients due to anovulatory cycles. Trial registration number not applicable

P-379 Ongoing pregnancy rate (OPR) of day (D) 7 euploid blastocysts is inferior to D5/D6 euploid blastocysts in frozen embryo transfer (FET) cycles

Abstract Study question Do delayed-grown D7 euploid blastocysts have similar OPRs as D5 or D6 euploid blastocysts in FET cycles? Summary answer Although OPR is significantly higher with D5/D6 euploid blastocysts than D7, patients aged &amp;gt;38 years might benefit when slow-developing blastocysts are routinely cultured till D7. What is known already Current IVF practice suggests that embryos of optimal development reach blastocyst stage 116±2 hours after insemination. Recently, high reproductive potential has been reported with D6 as well as with D7 blastocysts. Although D7 blastocysts have a delayed embryo development, euploidy rates range between 25% and 49% if biopsy is performed. Usable D7 blastocysts represent nearly 5% of embryos in IVF with acceptable pregnancy and live birth rates, however, data are still limited. Therefore, further evidence of FET outcomes with D5, D6 and D7 euploid blastocysts are needed to investigate whether prolonged in-vitro embryo culture till D7 should be performed routinely. Study design, size, duration A single centre observational study was performed between June 2017 and November 2021, including 1396 single euploid FET cycles with blastocysts biopsied on D5 (N = 795), D6 (N = 572) or D7 (N = 29). Patients underwent endometrial preparation for a FET in a natural cycle (NC) or hormone replacement treatment (HRT). Only blastocysts graded ≥ BL3CC (Gardner scoring) before trophectoderm (TE) biopsy on D5, D6 or D7, which re-expanded within 1-hour post-warming, were considered in the analysis. Participants/materials, setting, methods All warmed blastocysts were transferred after 120 hours of progesterone (P4) exposure. In NC, P4 was administered after ovulation until pregnancy test (PT). For HRT cycles, estradiol was prescribed until endometrial thickness reached ≥6 mm or a trilaminar pattern was seen on which P4 was supplemented until PT. OPR was recorded at 12 weeks by the presence of a gestational sac/s and fetal heartbeat. A multivariate logistic regression model with generalized estimating equation was performed. Main results and the role of chance Women’s mean age differed significantly for FET cycles performed with D5, D6 and D7 euploid blastocysts (33.2±5.6, 34.5±5.3 and 36.1±4.5 years old; P &amp;lt; 0.001) as well as AMH values (ng/mL) (3.6±3.6, 2.9±2.8 and 2.3±1.8; P &amp;lt; 0.001; respectively). OPR with D5 euploid blastocysts was significantly higher than D6 and D7 (55.6%, 44.9% and 10.3%; P &amp;lt; 0.001), however, miscarriage rates did not differ (9.3%, 6.6% and 6.9%; P = 0.201; respectively). Following an adjusted multivariate logistic regression model, the factors associated with a reduced OPR were: D7 FETs (OR: 0.19 [0.06-0.63]; P = 0.006), ICM grade C (OR: 0.29 [0.17-0.48]; P &amp;lt; 0.001) and TE grade C (OR: 0.58 [0.38-0.89]; P = 0.012). Contrary, OPR outcomes were increased in NC compared to HRT cycles (OR: 1.35 [1.06-1.71]; P = 0.013). A sub-analysis showed that advanced maternal age was a risk factor of having a D7 FET cycle (OR: 1.09 [1.01-1.17]; P = 0.025). In patients &amp;gt;38 years, OPR was improved if D7 FET cycles were performed however, this finding was nonsignificant (OR: 2.33 [0.19-29.4], P = 0.510). In patients &amp;lt;38 years, D7 FET cycles were significantly negatively associated with OPR outcomes (OR: 0.07 [0.01-0.54], P = 0.011). Regardless of patient’s age, OPR outcomes with D5/D6 were higher than D7 FETs. Limitations, reasons for caution The current results are based on an observational study including a limited sample size of D7 euploid blastocysts FET cycles. Additionally, live birth rates should be considered in a further analysis to validate the performance of D5 and D6, compared to D7 euploid blastocysts, in both, NC and HRT cycles. Wider implications of the findings Considering age as a risk factor of having delayed grown blastocysts in-vitro, culturing embryos till D7 can be a strategy to increase OPR in patients &amp;gt;38 years old. With an increase in age, patients are more likely to have blastocysts biopsied on D6/D7. OPR outcomes are increased in NC FETs. Trial registration number non-clinical trials

Endometrial compaction does not predict live birth in single euploid frozen embryo transfers: a prospective study.

Is there a relationship between endometrial compaction and live birth in euploid frozen embryo transfer (FET) cycles? Live birth rates (LBRs) were similar in both patients that demonstrated endometrial compaction or no compaction in single euploid FETs. There has been increasing interest in the correlation between endometrial compaction and clinical outcomes but there has been conflicting evidence from prior investigations. This was a prospective observational study from 1 September 2020 to 9 April 2021. This study was performed at a single, academically affiliated fertility center in which patients who had an autologous single euploid FET using a programmed or modified natural cycle protocol were included. All embryos had trophectoderm biopsy for preimplantation genetic testing for aneuploidy followed by vitrification at the blastocyst stage. Two ultrasound measurements of endometrial thickness (EMT) were obtained. The first measurement (T1) was measured transvaginally within 1 day of initiation of progesterone or ovulation trigger injection, and a second EMT (T2) was measured transabdominally at the time of embryo transfer (ET). The primary outcome (LBR) was based on the presence and proportion of compaction (percentage difference in EMT between T1 and T2). Of the 186 participants included, 54%, 45%, 35%, 28% and 21% of women exhibited >0%, ≥5%, ≥10%, ≥15% and ≥20% endometrial compaction, respectively. Endometrial compaction was not predictive of live birth at any of the defined cutoffs. A sub-analysis stratified by FET protocol type (n = 89 programmed; n = 97 modified natural) showed similar results. There was the potential for measurement error in the recorded EMTs. The T2 measurement was performed transabdominally, which may cause potential measurement error, as it is generally accepted that transvaginal measurements of EMT are more accurate, though, any bias is expected to be non-differential. The sub-analysis performed looking at FET protocol type was underpowered and should be interpreted with caution. Our study, however, represents a pragmatic approach, as it allowed patients to avoid having to come in for an extra transvaginal ultrasound the day before or on the day of ET. Assessing endometrial compaction may lead to unnecessary cycle cancellation. However, further studies are needed to determine if routine screening for endometrial compaction would improve clinical outcomes. No authors report conflicts of interest or disclosures. There was no study funding. NCT04330066.

Live birth rate following a euploid blastocyst transfer is not affected by double vitrification and warming at cleavage or blastocyst stage.

To compare reproductive outcomes following a euploid embryo transfer, between those embryos vitrified-warmed twice to those vitrified-warmed once. We retrospectively analysed 694 single euploid frozen embryo transfer cycles following preimplantation genetic testing for aneuploidy (PGT-A). For cycles in group 1 (N = 451), embryos were biopsied for PGT-A at blastocyst stage and vitrified. For cycles in group 2 (N = 146), embryos were vitrified at blastocyst stage, before being warmed and biopsied for PGT-A and vitrified again. For cycles in group 3 (N = 97), embryos were vitrified on day-3, before being warmed, cultured to day-5 and biopsied for PGT-A and re-vitrified. The pregnancy, clinical pregnancy and livebirth rate in group 2 were not statistically different to group 1 (pregnancy rate, adjusted OR 1.09, 95% CI 0.62-1.91; clinical pregnancy, aOR 0.89, 95% CI 0.58-1.37; live birth rate, aOR 0.85, 95% CI 0.56-1.28). There was also no significant difference between group 3 and group 1, with similar pregnancy rate (aOR 1.22, 95% CI 0.74-1.99), clinical pregnancy rate (aOR 1.21, 95% CI 0.75-1.96) and live birth rate (aOR 1.15, 95% CI, 0.73-1.80). There was no significant difference in miscarriage rates between all three groups. The age at the oocyte collection, embryo quality and day of biopsy were associated with pregnancy, clinical pregnancy and live birth rate. This study suggests that vitrifying and warming embryos twice at blastocyst or at cleavage and then blastocyst stage, can lead to similar reproductive outcomes to embryos vitrified-warmed once, after a single euploid embryo transfer.

Euploid day 7 blastocysts of infertility patients with only slow embryo development have reduced implantation potential

Research questionWhat is the reproductive potential of embryos that achieve blastulation on day 7 followed by preimplantation genetic testing for aneuploidies (PGT-A) for infertility patients with slow embryo development? DesignThis was a retrospective cohort study in a private IVF clinic of consecutive female infertility patients (n = 2966) aged 24–48 (36.3 ± 3.8) years who underwent frozen embryo transfer (FET) of a single euploid blastocyst. ResultsThe women underwent single euploid FET of an embryo that achieved blastulation on day 5 (n = 1880), day 6 (n = 986) or day 7 (n = 100). Day 7 embryos resulted in lower implantation and live birth rates compared with both day 5 and day 6 embryos (P < 0.001). The day 5, day 6 and day 7 groups had 68.5%, 55.2% and 36.0% live birth rates, respectively. The day 7 group was older than the day 5 group (P < 0.001); comparing age-matched cohorts, the day 7 group still had lower implantation and live birth rates (P < 0.0001 and P < 0.001, respectively). Embryo grade was unrelated to live birth rates. Day 7 embryos of expansion grade 5 or 6 or trophectoderm grade A were more likely to be euploid compared with expansion grade 3 or trophectoderm grade B. ConclusionsEuploid day 7 embryos represented reduced implantation potential, even when controlling for maternal age. Of all day 7 embryos that underwent PGT-A, euploidy was associated with expansion grade 5 or 6 and trophectoderm grade A. These results can help providers manage patient expectations in cases where infertile women have slow embryo development.

ENDOMETRIAL COMPACTION DOES NOT PREDICT CLINICAL PREGNANCY IN SINGLE EUPLOID FROZEN EMBRYO TRANSFERS: A PROSPECTIVE OBSERVATIONAL STUDY

To investigate the relationship between endometrial compaction and clinical pregnancy rate (CPR) in euploid frozen embryo transfer (FET) cycles. In this prospective observational study at a large academically-affiliated center, we included patients 18 to 43 years old who had an autologous single euploid FET with ≥7 mm endometrial thickness (EMT) on transvaginal ultrasound (TVUS). We excluded patients with body mass index >40 or <18.5 kg/m2, those using a gestational carrier, a history of ≥2 miscarriages, uterine factors, or a prior endometrial receptivity assay biopsy. All embryos had preimplantation genetic testing for aneuploidy (PGT-A) followed by vitrification at the blastocyst stage. FET protocols consisted of both programmed hormone replacement or natural cycles. We measured the initial EMT (T1) with TVUS within 1 day of initiation of progesterone or ovulation trigger injection. The second EMT (T2) was measured transabdominally at the embryo transfer. Endometrial compaction was calculated as the percent difference in EMT between T1 and T2. All T1 and T2 images were screened by a physician to ensure that the recorded EMTs were accurate. The primary outcome was CPR (gestational sac with fetal heartbeat on ultrasound between 6 to 9 weeks’ gestation). We compared CPR between those with and without compaction at various cutoffs (>0%, ≥5%, ≥10%, ≥15%, and ≥20%) using a chi-square test, and we calculated sensitivity, specificity, and positive negative predictive values of each cutoff. We considered P<0.05 to be statistically significant. The present study was adequately powered according to an apriori calculation. Of the 160 patients included, 75% were undergoing their first FET and 10% had a prior fresh embryo transfer. Only 30.6% patients exhibited any degree of compaction. Compaction was not predictive of CPR at any of the defined cutoffs (Table 1). A sub-analysis stratified by FET protocol type showed similar results. Endometrial compaction was not predictive of clinical pregnancy in single euploid FETs in the overall cohort nor by FET protocol type.

THE HYPOTHESIS OF PREFERENCIAL LOSS OF FEMALE EMBRYOS: EMBRYONIC SEX IS NOT ASSOCIATED WITH INCREASED ODDS OF EARLY PREGNANCY LOSS

The human sex ratio has long interested developmental biologists, statisticians, and other scientists. Primary Sex Ratio (PSR) in humans has been thought to be male-biased. Previously published studies about PSR have suggested this bias is due to a preferential loss of female conceptuses during the earliest stages of pregnancy1,2. To date, the dynamics of PSR from conception to birth are poorly understood. Literature about PSR is currently based on subjective estimates, extrapolations from large historical cohorts, or based on data sourced from natural conceptions3. Yet, the use of data from patients who undergo ART treatment presents an opportunity to observe embryonic sex prior to transfer through the application of PGT. This study aims to analyze whether the selection of female embryos prior to frozen embryo transfer (FET) are at higher risk of suffering early pregnancy loss as compared to the selection of male embryos. The study included patients who underwent a single euploid FET cycle from 2016-2021. Gender selection for family balancing cases were excluded from the analysis. PGT-A with NGS was performed for all cases. Cohorts were segregated into groups based on embryonic sex prior to transfer selection. Only top morphology embryos with a grade ≥4AA (Modified Gardner’s) were included in the study. Patient demographics and IVF cycle outcomes were recorded. Biochemical pregnancy loss (BPL) was defined as detectible serum ß-hCG and embryonic arrest prior to the development of a clinical pregnancy. Clinical pregnancy loss (CPL) was defined as the loss of a pregnancy diagnosed by ultrasonographic visualization of one or more gestational sacs. Comparative statistics and an adjusted mixed model with a GEE were utilized for statistical analyses. A sample size of 906 single, euploid FETs per cohort was calculated to ensure an 80% power to detect a difference of 5% on clinical pregnancy loss rates (α=0.05). 1,363 male were compared to 1,045 female FETs. No differences were found in patient’s age, BMI, AMH, endometrial thickness and other demographic variables between cohorts. Also, no differences were found in implantation, clinical pregnancy, ongoing pregnancy, BPL and CPL. After adjusting for age, BMI, AMH, day of biopsy and endometrial thickness, no association was found between embryo sex and increased odds of BPL (OR 0.50 CI95% 0.11-2.27, p=0.37); or CPL (OR 0.28 CI95% 0.07-1.16, p=0.08). By analyzing a large cohort of single euploid embryo transfers, we can observe the proportion of pregnancy losses that are not associated with aneuploidy, thus assessing the differences on early pregnancy loss rates based on embryonic sex while adjusting for other important covariates. For patients who undergo IVF with subsequent PGT-A and FET, there does not appear to be increased odds of pregnancy loss in selecting a single, euploid female embryo compared to male embryo counterparts.

P–360 Blastocyst biopsy day does have an impact on clinical pregnancies in different frozen embryo transfer (FET) regimens: natural cycle (NC) versus hormone replacement therapy (HRT)

Abstract Study question Do euploid blastocysts biopsied on day (D) 5 or D6 differ in clinical pregnancy rates when single FET are performed in NC or HRT cycles? Summary answer In single FET cycles, euploid D5 blastocysts have higher clinical pregnancy rates than D6 in NC, while outcomes are comparable in HRT cycles. What is known already: The synchronization between the endometrium and the embryo development is fundamental for a successful implantation. When performing FET with euploid blastocysts biopsied on D5 or D6, higher clinical pregnancy rates have been reported with D5 blastocysts, however contradictory findings were described due to the study design heterogeneity and endometrial preparation (EP) protocol variabilities. In FET cycles, no consensus has been defined of the superiority of NC over HRT cycles when euploid blastocysts are transferred. Consequently, the question remains unanswered if the clinical pregnancy rates of single euploid FET with D5 or D6 blastocysts differ when the EP protocol remains constant. Study design, size, duration A single center observational study was performed between June 2017 and November 2020, including 1027 single euploid FET with blastocysts biopsied on D5 or D6. All patients with primary or secondary infertility who underwent a FET in a NC or HRT EP protocol, with blastocysts graded ≥ BL3CC (Gardner scoring system) prior to biopsy were included. Vitrified-warmed blastocysts that did not re-expand within 1-hour post-warming were excluded from the analysis. Participants/materials, setting, methods In NCs, vaginal progesterone (P4) (Endometrin®) was administrated (3x100mg) after endocrinological confirmation of ovulation until pregnancy test. For HRT cycles, oral estradiol administration was started on day 2 (4 mg) and increased to 6mg on D5 of the cycle. When endometrial thickness was ≥6 mm, P4 was given (3x100mg) until pregnancy test. All FET were performed on D5 after start of P4 administration. Clinical pregnancy was recorded as the presence of an intrauterine gestational sac. Main results and the role of chance Women’s mean age was 33.8 ± 5.5 years. A total of 651 FETs were performed with D5 euploid blastocysts (37.6% in NC and 62.4% in HRT) and 376 with D6 (43.1% in NC and 56.9% in HRT). Clinical pregnancy rate in NC was higher with D5 blastocysts compared to D6 (66.9% vs 50.0%; OR = 0.494, 95% CI = 0.322–0.758; p &amp;lt; 0.001), while no significant differences were found when vitrified-warmed blastocysts were transferred in HRT cycles (64.3% vs 58.4%; OR = 0.781, 95% CI = 0.548–1.112; p = 0.164). Additionally, clinical miscarriage was significantly higher with D5 euploid blastocysts transferred in NC (D5=10.9% vs D6=3.7%, OR = 0.239, 95% CI = 0.044–0.837; p = 0.019). In HRT, miscarriage outcomes were similar between D5 and D6 euploid blastocysts (D5=18.7% vs D6=20.8%, OR = 0.781, 95% CI = 0.548–1.112; p = 0.164), but significantly higher (p &amp;lt; 0.001) than in NC. From a multinomial logistic regression model including age, blastocyst quality and day of biopsy as confounding factors, the clinical pregnancy rate was significantly affected by D6 blastocyst biopsy (OR = 0.571, 95% CI = 0.360–0.906, p = 0.017) and inner cell mass (ICM) grade A (OR = 3.941, 95% CI = 1.149–10.402; p = 0.006) or B (OR = 2.601, 95% CI = 1.146–5.907, p = 0.022) in NC. In HRT cycles, exclusively ICM was statistically significant (OR = 2.555, 95% CI = 1.214–5.381, p = 0.015 and OR = 2.397, 95% CI = 1.286–4.470, p &amp;lt; 0.001 for grade A and B, respectively). Limitations, reasons for caution The current results are based on an observational retrospective study. Live birth and perinatal outcomes should be considered in a further analysis to evaluate the performance of the NC vs HRT protocols when D5 or D6 euploid blastocysts are transferred in FET cycles. Wider implications of the findings: While the clinical pregnancies of D5 and D6 euploid blastocysts are comparable in HRT protocols only, the miscarriage rates seem to be significantly increased as compared to NC. Further studies are required to personalize EP protocols based on the day of blastocyst biopsy in order to improve clinical outcomes. Trial registration number No

P–359 Blastocyst quality, transfer difficulty and endometrial thickness affect clinical pregnancy after frozen embryo transfer (FET) of euploid blastocysts in the upper uterine cavity

Abstract Study question Which factors affect the clinical pregnancy rate (CPR) after single euploid frozen embryo transfers (FET), when the blastocyst is transferred in the upper uterine cavity area? Summary answer Blastocyst quality, embryo transfer difficulty and endometrial thickness affect the CPR in FET. What is known already There is a limited understanding of the factors affecting success rates after FET. The most important factors influencing implantation rates are patient characteristics, type of endometrial preparation, embryo quality and transfer difficulty. It has been shown that the position of the euploid blastocyst, measured as distance from the fundus (DFF) of the uterine cavity (mm), affects the implantation potential. Although the ideal location within the uterine cavity is still being debated in very heterogeneous patient populations, most studies have found that the highest pregnancy rates are obtained when the embryo is placed in the upper area of the uterine cavity. Study design, size, duration This single center retrospective cohort study included a total of 603 single euploid FET cycles, in the upper half of the uterine cavity, between January 2019 and November 2020 in ART Fertility Clinic Abu Dhabi, UAE. Participants/materials, setting, methods Trophectoderm biopsy samples were subjected to Next Generation Sequencing to screen the ploidy state. Vitrification and warming were performed using the Cryotop method (Kitazato, Biopharma). The full length of the uterine cavity and the longitudinal distance between the fundal endometrial surface and the air bubble after transfer were measured. Main results and the role of chance The patients were on average 33.9 (19–46) years old. The FET was performed in a natural cycle (NC) (n = 278) or hormone replacement therapy (HRT) (n = 325). Of the 603 transfers which had been performed in the upper half of the uterus, 412 (68.3%) resulted in a pregnancy and 311 (51.5%) in a clinical pregnancy. After bivariate analysis, the clinical pregnancy rate was significantly higher for high quality blastocysts (grade 1–2 versus 3–4) (p &amp;lt; 0.001), after easy embryo transfers (p = 0.001) and for higher endometrial thickness (p = 0.027). After performing a multivariate logistic regression analysis to consider the effect of all explanatory variables (age, Anti Müllerian hormone, body mass index, endometrial thickness, quality of the blastocyst, difficulty of the transfer [requirement of additional instrumentation], presence of mucus or blood on the transfer catheter, day 5 or day 6 biopsy, FET endometrial preparation), the clinical pregnancy was affected by the endometrial thickness: OR 1.20 [1.05–1.37], p = 0.007; transfer difficulty: OR 0.44 [0.25–0.79], p = 0.006; blastocyst quality 3: OR 0.38 [0.18–0.79], p = 0.01 and blastocyst quality 4: OR 0.15 [0.06–0.37], p &amp;lt; 0.0001. Age did not affect the clinical pregnancy after transferring a single euploid blastocyst: OR 1.03 [1.00–1.06], p = 0.052. Limitations, reasons for caution The limitation of this study was its retrospective nature and the small sample size. Other parameters may be important in live birth outcomes. Wider implications of the findings: Optimization of clinical pregnancy outcomes after FET depends on multiple factors. Even after transfer of euploid blastocysts in the upper uterine cavity, the endometrial thickness, transfer difficulty and blastocyst quality will still affect the clinical pregnancy outcomes. Trial registration number NA

Routine endometrial receptivity array in first embryo transfer cycles does not improve live birth rate

To compare the live birth rate between patients who undergo personalized embryo transfer (pET) after endometrial receptivity array (ERA) versus frozen embryo transfer (FET) with standard timing in first single euploid FET cycles. To report the rate of displacement of the window of implantation (WOI) in an infertile population without a history of implantation failure. Prospective cohort study of patients who underwent their first single euploid programmed FET. Private fertility clinic. Patients who underwent first autologous single euploid programmed FET between January 2018 and April2019. Endometrial biopsy with ERA followed by pET as indicated. Live birth rate and rate of receptive and nonreceptive ERA. A total of 228 single euploid FET cycles were included in our analysis. Of those, 147 (64.5%) were ERA/pET cycles, and 81 (35.5%) were standard timing FET cycles. Endometrial receptivity array was receptive in 60/147 (40.8%) and nonreceptive in 87/147 (59.2%) patients. Nonreceptive ERAs were prereceptive in 93.1% of cases. The live birth rate did not differ between patients who underwent FET with standard timing and patients who underwent ERA/pET, 45/81 (56.6%) and 83/147 (56.5%), respectively. Our data do not support the routine use of ERA in an unselected patient population undergoing first autologous single euploid programmed embryo transfer.