Natural Cycle Frozen Embryo Transfer Research Articles

MiR-135a-5p regulates window of implantation by suppressing pinopodes development and decidualization of endometrial stromal cells.

The window of implantation (WOI) is a brief period during which the endometrium is receptive to embryo implantation. This study investigated the relationship between miR-135a-5p and endometrial receptivity. Peripheral blood was collected on the day of ovulation and the 5th day after ovulation for high-throughput sequencing from women who achieved clinical pregnancy through natural cycle frozen embryo transfer. RT-qPCR assessed miR-135a-5p expression in the endometrium tissue or cells during the mouse implantation window or decidualization. Scanning electron microscopy was utilized to observe pinopode morphology and quantity in mice overexpressing miR-135a-5p during the WOI. Human endometrial stromal cells (HESC) and artificial induction of mouse uterine decidualization were used to explore whether miR-135a-5p overexpression inhibits decidualization by regulating HOXA10 and BMPR2. Furthermore, the impact of miR-135a-5p on HESC proliferation and HTR8/SVneo invasion was explored. A total of 54 women were enrolled in the study. bioinformatics analysis and animal models demonstrated that miR-135a-5p was significantly downregulated during the WOI, and its high expression can lead to abnormal pregnancy outcomes. Overexpression of miR-135a-5p resulted in the absence of pinopode in mouse endometrial tissue during the WOI. High miR-135a-5p levels were found to potentially inhibit endometrial tissue decidualization by downregulating HOXA10 and BMPR2 expression. Finally, CEBPD was identified as a potential regulator of miR-135a-5p, which would explain the decreased miR-135a-5p expression during the WOI. MiR-135a-5p expression is significantly downregulated during the WOI. High miR-135a-5p levels suppress pinopode development and endometrial tissue decidualization through HOXA10 and BMPR2, contributing to inadequate endometrial receptivity.

Clinical Outcomes in Hormone Replacement Therapy (HRT)-Frozen Embryo Transfer (FET) Protocol Increased by Administering Gonadotropin-Releasing Hormone Agonist (GnRH) in the Initial Stage of the Luteal Phase: A Retrospective Analysis.

The objective of this study was to determine if gonadotropin-releasing hormone agonist (GnRH) administration supporting the luteal phase in frozen embryo transfer (FET) improves clinical outcomes Methods and materials This is a retrospective cohort study and we analyzed 3515 cycles of FET at the Department of Reproductive Medicine in our hospital from February 2018 through December 2021. Patients were divided into the GnRH (triptorelin+progesterone and human chorionic gonadotropin (hCG)) group and the non-GnRHa (existing treatment without triptorelin) group. There were 1033 and 2485 cases in the above groups, respectively. Live birth rates (LBR) and clinical pregnancy rates (CPR) were contrasted in the two groups. We found greater CPR (58.00% versus 48.40%, P-value = 0.003) and LBR (52.70% versus 45.60%, P-value = 0.001) for HRT-FET cycles, and found no clinical significance for natural cycle FET (NC-FET) (58.20% versus 52.90%, P-value = 0.364 and 54.40% versus 47.00%, P-value=0.211), GnRH+HRT-FET (53.00% versus 53.00%, P-value=0.176 and 46.20% versus 47.30%, P-value=0.794), and stimulation-FET (59.30% versus 52.90%, P-value=.00.566 and 59.30% versus 47.10%, P-value=.00.247) in terms of CPR and LBR in the two groups. There was a 47% increase in CPR in the GnRH group, and there was a 33% increase in LBR in the same group. During HRT-FET cycles, administering triptorelin three to four times in the existing luteal support can improve CPR and LBR, and administering triptorelin during the initial stage of the luteal phase can prove a new option for luteal support.

Progesterone concentrations on blastocyst transfer day in modified natural cycle frozen embryo transfer cycles

Research questionAre serum progesterone concentrations on the day of modified natural cycle (mNC) frozen blastocyst transfer (FET) without luteal phase support (LPS) associated with clinical pregnancy rate (CPR)? DesignData were collected between January 2019 and October 2022 as a sub-study of an ongoing randomized controlled trial assessing pregnancy outcomes in mNC-FET. The sub-study included all women (n = 209) randomized to mNC-FET without LPS at the time of data extraction. Participants were aged 18–41 years, had regular menstrual cycles and underwent mNC-FET treatment with single-blastocyst transfer. Associations between the serum progesterone concentration on the day of blastocyst transfer and CPR, pregnancy rate and pregnancy loss rate (PLR) were examined between groups with low and higher progesterone concentrations using the 25th and 10th percentiles as cut-offs. Multivariate logistic regression analyses were performed to adjust for potential confounding factors. ResultsProgesterone concentrations on the day of blastocyst transfer in mNC-FET without LPS ranged from 4.9 to 91.8 nmol/l, with the 25th and 10th percentiles at 29.0 nmol/l and 22.5 nmol/l, respectively. Serum progesterone concentrations did not differ between women with or without a clinical pregnancy (mean [SD] 38.5 [14.0] versus 36.8 [12.4] nmol/l; P = 0.350). Furthermore, the CPR, pregancy rate and PLR were similar in women with low or high progesterone concentrations when using the 25th or the 10th progesterone percentile as cut-off. Multivariate regression analyses showed no association between progesterone concentrations and CPR. ConclusionsNo association was found between progesterone concentration on the day of blastocyst transfer and pregnancy outcome in women undergoing mNC-FET without progesterone LPS.

Natural Cycle Frozen Embryo Transfer – What Does The Evidence Say?

Natural Cycle Frozen Embryo Transfer – What Does The Evidence Say?

Does luteal phase progesterone supplementation affect physical and psychosocial well-being among women undergoing modified natural cycle-FET? A sub-study of a randomized controlled trial.

Are there any differences in physical and psychosocial well-being among women undergoing modified natural cycle frozen embryo transfer (mNC-FET) with or without vaginal progesterone as luteal phase support (LPS)? Women undergoing mNC-FET with vaginal progesterone supplementation were more likely to experience physical discomfort but there was no difference in psychosocial well-being between the two groups. mNC-FET can be carried out with or without vaginal progesterone as LPS, which has several side-effects. It is commonly known that fertility treatment can cause stress and psychosocial strain, however, most studies on this subject are conducted in fresh cycle regimes, which differ from NC-FET and results may not be comparable. This is a sub-study of an ongoing RCT investigating whether progesterone supplementation has a positive effect on live birth rate in mNC-FET. The RCT is conducted at eight fertility clinics in Denmark from 2019 and is planned to end primo 2024. The sub-study is based on two questionnaires on physical and psychosocial well-being added to the RCT in August 2019. On the time of data extraction 286 women had answered both questionnaires. Women who had answered both questionnaires were included in the sub-study. Participants were equally distributed, with 143 in each of the two groups. Participants in both groups received the same questionnaires at two time-points: on cycle day 2-5 (baseline) and after blastocyst transfer. Participants in the progesterone group had administered progesterone for 7 days upon answering the second questionnaire. All items in the questionnaires were validated. Items on psychosocial well-being originate from the Copenhagen Multi-Centre Psychosocial Infertility-Fertility Problem Stress Scale (COMPI-FPSS) and from the Mental Health Inventory-5. Women receiving progesterone experienced more vaginal itching and/or burning than women in the non-progesterone group (P < 0.001). Women in the progesterone group also experienced more self-reported vaginal yeast infection, this was, however, not significant after adjustment for multiple testing (P/adjusted P = 0.049/0.881). No differences regarding psychosocial well-being were found between the two groups. Within the progesterone group, a shift toward feeling less 'downhearted and blue' was found when comparing response distribution at baseline and after blastocyst transfer (P < 0.001). All items on physical symptoms were self-reported. The item on vaginal yeast infection was therefore not diagnosed by a doctor. Inclusion in the study required a few extra visits to the clinic, participants who felt more burdened by fertility treatment might have been more likely to decline participation. Women who experienced a lot of side-effects to progesterone prior to this FET cycle, might be less likely to participate. Our results are in line with previous known side-effects to progesterone. Physical side-effects of progesterone should be considered before administration. The RCT is fully supported by Rigshospitalet's Research Foundation and a grant from Gedeon Richter. Gedeon Richter were not involved in the design of protocol nor in the conduction of the study or analysis of results. A.P., L.P., and N.I.-C.F. report grants from Gedeon Richter, Ferring and Merck with no relations to this study. N.I.-C.F. has received travel support from Ferring, Merck A/S, & Gideon Richter, and is the head of the steering committee for the Danish Fertility Guidelines made by the members of from the Danish Fertility Society. A.P. reports consulting fees from Preglem, Novo Nordisk, Ferring, Gedeon Richter, Cryos, & Merck A/S, honoraria from Gedeon Richter, Ferring, Merck A/S, Theramex, and Organon, has received travel support from Gedeon Richter (payment to institution), participated on an advisory board for Preglem and was loaned an embryoscope from Gedeon Richter to their institution. A.L.S. has stock options for Novo Nordisk B A/S. B.A. have received unrestricted grant from Gedeon Richter Nordic and Merck and honoraria for lectures from Gedeon Richter, Merck, IBSA, and Marckyrl Pharma. The RCT is registered on ClinicalTrials. gov (NCT03795220) and in EudraCT (2018-002207-34).

O-198 Obstetric and neonatal outcomes after natural frozen embryo transfer; results from a follow-up study of the Antarctica-2 RCT

Abstract Study question Do obstetric and neonatal outcomes of women who conceived through home-based monitoring of the ovulation in natural cycle frozen embryo transfer (NC-FET) differ compared to hospital-controlled monitoring of the ovulation in NC-FET using a hCG trigger? Summary answer We found no differences in obstetric and neonatal outcomes when home-based monitoring versus hospital-controlled monitoring of the ovulation in women undergoing NC-FET. What is known already NC-FET is associated with lower risk of adverse obstetric and neonatal outcomes compared with artificial cycle FET. The question of how to prepare the endometrium for FET, has now gained even more importance and taken on the dimension of safety into account as it should not simply be reduced to the basic question of effectiveness. Study design, size, duration Between April 10, 2018 and April 13, 2022, 1464 women were included in the Antarctica-2 RCT (n = 732 home-based monitoring and n = 732 hospital-controlled monitoring). For this study we performed a follow-up study in order to investigate obstetric and neonatal outcomes of the participating women with live births after the Antarctica-2 trial. Participants/materials, setting, methods We included only singleton livebirths. Main outcomes were gestational age, preterm birth (PTB), very preterm birth (very PTB), birth weight, large for gestational age (LGA) and small for gestational age (SGA). Additional outcomes included: gestational diabetes (GDM), hypertensive-disorders-of-pregnancy (HDP), pre-eclampsia (PE), abnormal placentation (including placenta previa and accrete), hospital admission during pregnancy, congenital anomalies and neonatal death. We calculated risk ratios and absolute risk differences (95% CI) using per protocol analysis. Main results and the role of chance Both studyarms resulted in similar live birth rates. Singleton live birth occured in 146 of 732 women (19.9%) following home-based and in 148 of 732 women (20.2%) following hospital-controlled monitoring. The mean gestational age in weeks was 39.0 (SD 0.3) for the home-based monitoring group versus 39.3 (SD 0.2) for the hospital-controlled monitoring group. We found no significant differences in preterm birth (5/146 versus 11/148, RR 1.00, 95% CI 0.90 – 1.10) or very preterm birth (1/146 versus 2/148, RR 1.00, 95% CI 0.90 – 1.10) for home-based versus hospital-based monitoring. Very preterm birth only occurred once in the home-based monitoring group. The mean birth weight was 3504.0 (SD 47.7) for the home-based monitoring group versus 3532.1 (SD 48.1) for the hospital-controlled monitoring group. We found no significant differences in LGA (20/146 versus 18/148, RR 1.00, 95% CI 0.90 – 1.10) and SGA (12/146 versus 12/148, RR 1.00, 95% CI 0.90 – 1.10) for home-based versus hospital-based monitoring. Also, no differences were found in HDP, PE, abnormal placentation, GDM, hospital admission during pregnancy and congenital anomaly. One neonatal death due to pulmonary hypoplasia occurred in the home-based monitoring group after very PTB. Limitations, reasons for caution The outcomes of HDP, PE, abnormal placentation, GDM and hospital admission during pregnancy were patient-reported and confirmed by hospital-files after contacting the participating centers. Wider implications of the findings NC-FET is the preferred treatment in women with ovulatory cycles undergoing FET. When home-based monitoring is compared to hospital-controlled monitoring in NC-FET we found no difference in obstetric or neonatal outcomes. Trial registration number not applicable

P-490 Impact of follicular phase characteristics on mid-luteal progesterone and ongoing pregnancy rates: Lessons learned from true natural cycle frozen embryo transfer

Abstract Study question Is there an association between follicular phase endocrine and ultrasonographic characteristics and ongoing pregnancy rates (OPRs) in true-natural cycle (t-NC) frozen embryo transfers (FETs)? Summary answer Endometrial thickness one day before ovulation is the only independent predictor of ongoing pregnancy (OP) in t-NC FET cycles. What is known already In ovulatory women, NC FET is currently being proposed instead of the hormonal replacement treatment (HRT) protocol since HRT is associated with increased maternal and obstetric risk factors, most probably due to the absence of a corpus luteum. However, the presence of ovulation in regularly cycling women does not guarantee a receptive endometrium. Currently, there is a lack of data regarding the impact of follicular phase endocrine and ultrasonographic parameters on mid-luteal progesterone (P4) levels and OPRs in t-NC FET cycles. Study design, size, duration A cohort study of 229 women who underwent warmed blastocyst transfer employing t-NC. Three strategies were adopted. During January 2017-June 2017, serum P4 was not monitored. During July 2017-June 2020, serum P4 was routinely monitored on the FET-1 day. During July 2020-August 2022, a rescue strategy with daily 25-mg subcutaneous progesterone was adopted for patients with P4 levels between 7-10 ng/mL. In patients with serum P4&amp;lt;7 ng/mL FET was cancelled. Participants/materials, setting, methods Staying in-town and having regular menstrual cycles, permitting intensive endocrine and ultrasonographic monitoring (daily serum estradiol [E2], luteinizing hormone [LH], P4, and transvaginal ultrasonography), starting mid-cycle until confirmation of ovulation was the only inclusion criteria. Only the first FET cycle per patient was included. The primary outcome measure was OPR. The impact of follicular phase endocrine and ultrasonographic parameters on serum P4 levels on the FET-1 day and OPRs were evaluated using regression analysis. Main results and the role of chance Follicular phase parameters, including follicular phase length, late follicular phase E2, LH, P4 levels, and maximal follicle diameter before ovulation, were not significant predictors of ongoing pregnancy (OP) in t-NC FET. In contrast, the endometrial thickness one day prior to ovulation was a significant independent predictor of OP (adjusted OR = 1.29, 95% CI:1.06-1.56). When endometrial thickness before ovulation was assessed in quartiles, univariate OPRs in the 25th (&amp;lt;9.1 mm), 25-50th (9.1-10.1mm), 51-75th (10.2-11.6 mm) and &amp;gt;75th (&amp;gt;11.6 mm) percentiles were 43.3%, 47.3%, 71.7%, and 54.7%, respectively (p=0.016). Following logistic regression analysis, the adjusted ORs for OPR of the 51-75th (3.69, 95% CI:1.42-9.56) and &amp;gt;75th (2.86, 95% CI: 1.06-7.73) percentiles were significantly higher when compared with that of &amp;lt; 25th. The three strategies for monitoring/acting (rescue if needed) based on serum P4 levels on the FET-1 day were associated with similar adjusted ORs for OP. Notably, cancellation of cycles with serum P4 &amp;lt;7 ng/mL and adopting a rescue policy for those with 7-10 ng/mL did not increase OPRs. After multivariate linear regression analysis, late follicular E2 levels (ß-coefficient: 0.399 ng/mL, 95% CI:0.007;0.021) and BMI (ß-coefficient: −0.292 ng/mL, 95% CI: −0.730;-0.222) were the only significant predictors of P4 levels on the FET-1 day. Limitations, reasons for caution Limitations include the cohort study design evaluating three different policies, the single point serum P4 assessment, and adopting an arbitrary lower cut-off of &amp;lt; 7 ng/mL for cycle cancellation and 7-10 ng/mL for a rescue strategy. Wider implications of the findings Endometrial thickness one day before ovulation was the only significant predictor of OP in t-NC FET cycles. Apart from endometrial thickness, none of the follicular phase parameters were significant predictors of OP. Single-point assessment of serum P4 may not be reliable when assessing reproductive outcomes in t-NC FET. Trial registration number Not applicable

P-369 An innovative approach for FET that does not rely on the luteinizing hormone surge or human chorionic gonadotropin: a natural cycle with luteal support

Abstract Study question Can progestin supplementation in natural cycle, without reliance on LH surge or hCG ovulation triggering, effectively prepare the endometrium for a frozen embryo transfer (FET)? Summary answer High pregnancy rates can be achieved in natural cycle using luteal support as the main method for endometrial synchronization, without relying on the LH surge What is known already In recent years, frozen-thawed embryo transfer has become widely adopted and plays a significant role in assisted reproductive technology. To date, the evidence suggests that natural cycles result in higher pregnancy rates and fewer obstetric complications compared to hormonal replacement therapy, however, the most effective method for preparing the endometrium has not yet been determined. For transfer in the natural cycle specifically, conflicting results have been reported in terms of the outcome following spontaneous or triggered ovulation. No research is available that supports a natural cycle FET without monitoring the endogenous LH surge or using hCG trigger. Study design, size, duration This is a prospective analysis of 508 natural FET cycles between March 2019 and December 2022, including patients receiving embryos with own oocytes (339) and donated oocytes (169). Participants/materials, setting, methods All patients underwent ultrasound monitoring and serum hormone levels determination of estrogen and progesterone in 3 moments of the cycle (the day of the start of luteal support, 1 week before B-HCG and the day of B-HCG). Upon ultrasound confirmation of the endometrium's optimal thickness and appearance and the presence of the pre-ovulatory follicle, patients began progesterone supplementation and the day for FET was scheduled. Main results and the role of chance A clinical pregnancy rate of 65.48% was reported with a miscarriage rate of 9.09%. A higher rate of miscarriage (22.22%) was found to be associated with an endometrial thickness of less than 7mm at the time of progesterone initiation. The size of the dominant follicle did not affect pregnancy outcome, but a higher pregnancy rate was observed when the follicle measured 15 mm or larger (CPR of 66.83% in cycles with a follicle ≥15mm versus CPR of 60.22% in cycles with a follicle &amp;lt;15mm). Estrogen levels decline in the second measurement but increase again on the day of a positive beta test. This protocol requires less monitoring compared to true and modified natural cycles and is convenient to coordinate with oocyte recipients. A thin endometrial lining, measured below 7mm, increases the risk of a clinical miscarriage. A lack of increase in estrogen levels on the day of B-hCG is an unfavorable sign for a positive outcome. Limitations, reasons for caution Our analysis of data has a prospective design, although it may be limited by unmeasured factors such as the number, stage, and chromosomal testing of transferred embryos. Wider implications of the findings Supplementary luteal support does not affect the natural progression of the endometrium towards receptiveness and results in a key intervention for controlling the start, length and functionality of the window of implantation. A natural cycle, with progesterone supplementation but without monitoring the LH surge, results in high pregnancy rates. Trial registration number Not applicable

P-659 Natural cycle versus medically programmed cycle in frozen embryo transfer: a retrospective analysis

Abstract Study question Does frozen embryo transfer (FET) in natural cycle (NC) and programmed cycle (PC) differ in achieving live birth, and what are the confounding factors? Summary answer The probability of live birth was significantly higher in natural cycle FET compared to programmed cycle. What is known already FET can be performed in natural or programmed (hormonally modified) cycle but the data regarding the most optimal preparation of the endometrium remains conflicting and inconclusive. The latest Cochrane review (Glujovsky, 2020) including very low- to moderate-quality evidence could not demonstrate superiority of either protocol on life birth rate or other pregnancy outcomes. Study design, size, duration This is a retrospective single center registry study including all frozen embryo transfers performed at Helsinki University Hospital Reproductive Medicine Unit during 2016-2020. Main outcome measure was live birth and secondary outcomes were biochemical pregnancy, ectopic pregnancy and miscarriage. The study cohort included 5435 attempted frozen embryo transfers to 1913 women, of which 1735 cycles were cancelled, mostly due a poor cycle or a weekend in a 5-day clinic, and 3700 were performed. Participants/materials, setting, methods Study included 2581 FETs in NC and 1119 in PC. The collected data included patient and male partner age, BMI, smoking, underlying health conditions, causes of infertility, endometrial thickness, embryo quality classification and the pregnancy outcome. Embryos from donor oocytes were excluded. To assess the effect of different confounding factors, we performed a regression analysis with a generalized linear mixed model. Main results and the role of chance Mean age of the women in the PC group was slightly younger (33.5, 33.0-33.9 years) than in the NC group (34.5, 34.1-34.5 years; P &amp;lt; 0.001) years. Mean BMI was not statistically different (NC 24.2 vs PC 25.1 kg/m2), but significantly more women with BMI above 30 (PC 19.5% vs NC 10.2%; P &amp;lt; 0.001), as well as women with ovulation disorder (PC 67.2% vs NC 5.2%) were observed in the PC group. Smoking was more common in the NC group compared to the PC group (5.9 vs 4.0%, P &amp;lt; 0.001). Mean endometrial thickness at check-up visit prior to FET was 8.3 (8.1-8.5) mm in the PC group compared to 7.7 (7.6-7.8; P &amp;lt; 0.001) mm in the NC group. We observed a lower live birth rate in the PC group (23.3%) compared to the NC group (29.1%, OR 0.74, 95% CI 0.63-0.87). However, when adjusted with most significant confounding factors (female age, embryo quality score and tubal factor) the effect of the FET protocol on LBR was diminished. Incidence of miscarriage was higher in the PC group compared to the NC group, but no statistically significant difference was observed in the other secondary outcomes of biochemical pregnancy or ectopic pregnancy. Limitations, reasons for caution Retrospective design may include a selection bias between the study groups, although the demographic characteristics of the groups were quite comparable. Wider implications of the findings Confounding factors seem to explain much of the inferiority of programmed cycle compared to the natural cycle in terms of achieving live birth. However, prospective, randomized controlled trials including women with normal, ovulatory cycle would be needed to conclusively assess the optimal FET protocol. Trial registration number N/A

Are systemic progesterone levels in true natural cycle euploid frozen embryo transfers with luteal phase support predictive for ongoing pregnancy rates?

Are serum progesterone (P4) levels on the embryo transfer (ET) day predictive of ongoing pregnancy (OP) following a single euploid blastocyst transfer in a natural cycle (NC) when luteal phase support is routinely given? In single euploid frozen ETs in NC, P4 levels on ET day are not predictive for OP, when luteal phase support (LPS) is routinely added after the ET. In an NC frozen embryo transfer (FET), P4 produced by the corpus luteum initiates secretory transformation of the endometrium and maintains pregnancy after implantation. There are ongoing controversies on the existence of a P4 cutoff level on the ET day, being predictive for the chance of OP as well as of the possible role of additional LPS after ET. Previous studies in NC FET cycles, evaluating and identifying P4 cutoff levels did not exclude embryo aneuploidy as a possible reason for failure. This retrospective study analyzed single, euploid FET in NC, conducted in a tertiary referral IVF centre between September 2019 and June 2022, for which measurement of P4 on the day of ET and the treatment outcomes were available. Patients were only included once into the analysis. Outcome was defined as OP (ongoing clinical pregnancy with heartbeat, >12 weeks) or no-OP (not pregnant, biochemical pregnancy, early miscarriage). Patients with an ovulatory cycle and a single euploid blastocyst in an NC FET cycle were included. Cycles were monitored by ultrasound and repeated measurement of serum LH, estradiol, and P4. LH surge was identified when a rise of 180% above the previous level occurred and P4 levels of ≥1.0 ng/ml were regarded as confirmation of ovulation. The ET was scheduled on the fifth day after P4 rise and vaginal micronized P4 was started on the day of ET after P4 measurement. Of 266 patients included, 159 (59.8%) patients had an OP. There was no significant difference between the OP- and no-OP-groups for age, BMI, and day of embryo biopsy/cryopreservation (Day 5 versus Day 6). Furthermore, P4 levels were not different between the groups of patients with OP (P4: 14.8 ng/ml (IQR: 12.0-18.5 ng/ml)) versus no-OP (P4: 16.0 ng/ml (IQR: 11.6-18.9 ng/ml)) (P = 0.483), and no differences between both groups, when P4 levels were stratified into categories of P4 levels of >5 to ≤10, >10 to ≤15, >15 to ≤20, and >20 ng/ml (P = 0.341). However, both groups were significantly different for the embryo quality (EQ), defined by inner cell mass/trophectoderm, as well as when stratified into three EQ groups (good, fair, and poor) (P = 0.001 and 0.002, respectively). Stratified EQ groups remained the only significant parameter influencing OP in the uni- and multivariate analyses (P = 0.002 and P = 0.004, respectively), including age, BMI, and P4 levels (each in categories) and embryo cryopreservation day. Receiver operator characteristic curve for the prediction of an OP revealed an AUC of 0.648 when age, BMI and EQ groups were included into the model. The inclusion of P4 measurement on ET day into the model did not add any benefit for OP prediction (AUC = 0.665). The retrospective design is a limitation. Monitoring serum P4 levels can be abandoned in NC FET cycles with routine LPS as they do not seem to be predictive of live birth. No external funding was used for this study. The authors state that they do not have any conflicts of interest. N/A.

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

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.). 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. 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. 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.

Pregnancy and neonatal outcomes of letrozole versus natural cycle frozen embryo transfer of autologous euploid blastocyst.

To investigate the pregnancy and neonatal outcomes of letrozole-stimulated frozen embryo transfer (LTZ-FET) cycles compared with natural FET cycles (NC-FET). Our retrospective cohort included all LTZ-FET (n = 161) and NC-FET (n = 575) cycles that transferred a single euploid autologous blastocyst from 2016 to 2020 at Stanford Fertility Center. The LTZ-FET protocol entailed 5mg of daily letrozole for 5days starting on cycle day 2 or 3. Outcomes were compared using absolute standardized differences (ASD), in which a larger ASD signifies a larger difference. Multivariable regression models adjusted for confounders: maternal age, BMI, nulliparity, embryo grade, race, infertility diagnosis, and endometrial thickness. The demographic and clinical characteristics were overall similar. A greater proportion of the letrozole cohort was multiparous, transferred high-graded embryos, and had ovulatory dysfunction. The cohorts had similar pregnancy rates (67.1% LTZ vs 62.1% NC; aOR 1.31, P = 0.21) and live birth rates (60.9% LTZ vs 58.6% NC; aOR 1.17, P = 0.46). LTZ-FET neonates on average were born 5.7days earlier (P < 0.001) and had higher prevalence of prematurity (18.6% vs. 8.0%NC, ASD = 0.32) and low birth weight (10.4% vs. 5.0%, ASD = 0.20). Both cohorts' median gestational ages (38weeks and 1day for LTZ; 39weeks and 0day for NC) were full term. There were similar rates of pregnancy and live birth between LTZ-FET and NC-FET cycles. However, there was a higher prevalence of prematurity and low birth weight among LTZ-FET neonates. Reassuringly, the median gestational age in both cohorts was full term, and while the difference in gestational length of almost 6days does not appear to be clinically significant, this warrants larger studies.

Natural Cycle Frozen Embryo Transfer: Evaluating Optimal Protocols for Preparation and Timing.

While natural cycle frozen embryo transfer (NC-FET) is becoming increasingly common, significant practice variation exists in the use of ovulation induction medications, administration of ovulation trigger, and timing of embryo transfer without consensus as to the optimal protocol. The objective of this study is to evaluate the association of key aspects of the NC-FET protocol with implantation, pregnancy and live birth. This was a retrospective cohort study of blastocyst stage NC-FET cycles from October 2019 to July 2021 at a single academic fertility centre. Protocols varied between cycles across three key parameters which were evaluated as primary predictors of cycle outcomes: (1) use of letrozole for mild ovarian stimulation/ovulation induction, (2) administration of exogenous ovulation trigger versus spontaneous luteinising hormone surge and (3) transfer timing based on ovulation trigger versus sequential progesterone monitoring. Primary outcomes included implantation rate, clinical pregnancy and ongoing pregnancy. Generalised estimating equations were fitted to obtain adjusted odds ratios or rate ratios as appropriate with 95% confidence intervals for each outcome across the three primary predictors. A total of 183 cycles from 170 unique patients were eligible for inclusion. The average implantation rate was 0.58, resulting in an overall clinical pregnancy and ongoing pregnancy rate of 59.0% and 51.4%, respectively. After adjusting for age at embryo freeze and history of a failed embryo transfer, there were no significant associations between any predictor and implantation rate, clinical pregnancy, ongoing pregnancy, or live birth. In NC-FET, a variety of preparation and timing protocols may lead to comparable cycle outcomes, potentially allowing for flexibility on the basis of patient and physician preference. These findings warrant validation in a larger, randomised trial.

DOES THE RATE OF PROGESTERONE RISE PREDICT THE LIKELIHOOD OF IMPLANTATION FOLLOWING NATURAL CYCLE EUPLOID FROZEN EMBRYO TRANSFER?

The ideal monitoring protocol for natural cycle frozen embryo transfer (NC-FET) has yet to be established. Because progesterone is released by the corpus luteum following ovulation, the rate of progesterone rise may serve as a proxy for the health of the corpus luteum and therefore be a useful predictor of implantation.

NATURAL CYCLE FROZEN EMBRYO TRANSFER: EVALUATING OPTIMAL PROTOCOLS FOR PREPARATION AND TIMING

While natural cycle frozen embryo transfer (NC-FET) is becoming increasingly common, significant practice variation exists in the use of ovulation induction medications, administration of ovulation trigger, and timing of embryo transfer, without consensus as to the optimal protocol.

Programmed frozen embryo transfer cycle increased risk of hypertensive disorders of pregnancy: a multicenter cohort study in ovulatory women

Although live birth rates were comparable between programmed and natural frozen-thawed embryo transfer cycles, recent data showed that pregnancies after programmed cycle were associated with an increased risk of adverse perinatal outcomes, such as hypertensive disorders of pregnancy. Such a difference might be attributed to selection bias because patients with ovulation disorders are more likely to receive programmed endometrial preparation protocol than natural cycle. This study aimed to analyze whether programmed endometrial preparation protocol is associated with an increased risk of adverse perinatal outcomes compared with natural cycle during frozen embryo transfer in ovulatory women. This regional multicenter retrospective cohort study was conducted in 5 reproductive medical centers in Southeast China. Patients with regular cycles (21-35 days), who underwent either programmed or natural cycle blastocyst frozen embryo transfer and delivered singleton live birth babies after 28 weeks of gestation between 2016 and 2019 were analyzed. Each patient only contributed 1 cycle per cohort. The patients' frozen embryo transfer treatment cycles were linked to their obstetrical medication record, and a comprehensive medical record review was conducted to compare the maternal and neonatal outcomes between natural cycle and programmed cycle. Crude and adjusted odds ratios with 95% confidence intervals were calculated, and adjustment was made for relevant confounders. Study samples included 499 natural cycle frozen embryo transfer cases and 900 programmed frozen embryo transfer cases. Pregnancies after programmed cycle were associated with increased odds of hypertensive disorders of pregnancy (adjusted odds ratio, 2.71; 95% confidence interval, 1.59-4.91) and preeclampsia (adjusted odds ratio, 2.71; 95% confidence interval, 1.17-6.23) compared with pregnancies after natural cycle. No significant difference was detected regarding other adverse perinatal outcomes between the 2 endometrial protocols. In subgroup analysis, both the subgroups of hormone replacement therapy and hormone replacement therapy with gonadotrophin-releasing hormone analogue pretreatment had increased odds of developing hypertensive disorders of pregnancy than the natural cycle group. The risk of developing preeclampsia was higher in the hormone replacement therapy with gonadotrophin-releasing hormone analogue pretreatment subgroup than in the other 2 groups (adjusted odds ratio, 4.99; 95% confidence interval, 1.94-12.82) (aOR, 2.47; 95% CI, 1.17-5.18). Pregnancies after programmed frozen embryo transfer were associated with higher risks of hypertensive disorders of pregnancy in ovulatory women. The hormone replacement therapy with gonadotrophin-releasing hormone analogue pretreatment cycle led to the highest risk of preeclampsia among the 3 protocols.

The effect of frozen embryo transfer regimen on the association between serum progesterone and live birth: a multicentre prospective cohort study (ProFET).

What is the association between serum progesterone levels on the day of frozen embryo transfer (FET) and the probability of live birth in women undergoing different FET regimens? Overall, serum progesterone levels <7.8 ng/ml were associated with reduced odds of live birth, although the association between serum progesterone levels and the probability of live birth appeared to vary according to the route of progesterone administration. Progesterone is essential for pregnancy success. A recent systematic review showed that in FET cycles using vaginal progesterone for endometrial preparation, lower serum progesterone levels (<10 ng/ml) were associated with a reduction in live birth rates and higher chance of miscarriage. However, there was uncertainty about the association between serum progesterone levels and treatment outcomes in natural cycle FET (NC-FET) and HRT-FET using non-vaginal routes of progesterone administration. This was a multicentre (n = 8) prospective cohort study conducted in the UK between January 2020 and February 2021. We included women having NC-FET or HRT-FET treatment with progesterone administration by any available route. Women underwent venepuncture on the day of embryo transfer. Participants and clinical personnel were blinded to the serum progesterone levels. We conducted unadjusted and multivariable logistic regression analyses to investigate the association between serum progesterone levels on the day of FET and treatment outcomes according to the type of cycle and route of exogenous progesterone administration. Our primary outcome was the live birth rate per participant. We studied a total of 402 women. The mean (SD) serum progesterone level was 14.9 (7.5) ng/ml. Overall, the mean adjusted probability of live birth increased non-linearly from 37.6% (95% CI 26.3-48.9%) to 45.5% (95% CI 32.1-58.9%) as serum progesterone rose between the 10th (7.8 ng/ml) and 90th (24.0 ng/ml) centiles. In comparison to participants whose serum progesterone level was ≥7.8 ng/ml, those with lower progesterone (<7.8 ng/ml, 10th centile) experienced fewer live births (28.2% versus 40.0%, adjusted odds ratio [aOR] 0.41, 95% CI 0.18-0.91, P = 0.028), lower odds of clinical pregnancy (30.8% versus 45.1%, aOR 0.36, 95% CI 0.16-0.79, P = 0.011) and a trend towards increased odds of miscarriage (42.1% versus 28.7%, aOR 2.58, 95% CI 0.88-7.62, P = 0.086). In women receiving vaginal progesterone, the mean adjusted probability of live birth increased as serum progesterone levels rose, whereas women having exclusively subcutaneous progesterone experienced a reduction in the mean probability of live birth as progesterone levels rose beyond 16.3 ng/ml. The combination of vaginal and subcutaneous routes appeared to exert little impact upon the mean probability of live birth in relation to serum progesterone levels. The final sample size was smaller than originally planned, although our study was adequately powered to confidently identify a difference in live birth between optimal and inadequate progesterone levels. Furthermore, our cohort did not include women receiving oral or rectal progestogens. Our results corroborate existing evidence suggesting that lower serum progesterone levels hinder FET success. However, the relationship between serum progesterone and the probability of live birth appears to be non-linear in women receiving exclusively subcutaneous progesterone, suggesting that in this subgroup of women, high serum progesterone may also be detrimental to treatment success. This work was supported by CARE Fertility and a doctoral research fellowship (awarded to P.M.) by the Tommy's Charity and the University of Birmingham. M.J.P. is supported by the NIHR Birmingham Biomedical Research Centre. S.F. is a minor shareholder of CARE Fertility but has no financial or other interest with progesterone testing or manufacturing companies. P.L. reports personal fees from Pharmasure, outside the submitted work. G.P. reports personal fees from Besins Healthcare, outside the submitted work. M.W. reports personal fees from Ferring Pharmaceuticals, outside the submitted work. The remaining authors have no conflict of interest to declare. ClinicalTrials.gov: NCT04170517.

P-784 Less obstetric and neonatal outcomes after natural versus artificial cycle frozen embryo transfer

Abstract Study question Do obstetric and neonatal outcomes of women who conceived through natural cycle frozen embryo transfer (NC-FET) differ compared to an artificial cycle (AC-FET) method? Summary answer Fewer obstetric and neonatal complications after NC-FET were found compared with AC-FET. What is known already The number of FET has increased dramatically over the past decade, mainly due to improvement in laboratory techniques. Based on current evidence, there is no difference in pregnancy rates when NC-FET is compared to AC-FET in subfertile women with regular ovulatory cycles. However NC-FET seems to be associated with lower risk of adverse obstetric and neonatal outcomes compared with AC-FET cycles. The question of how to prepare the endometrium for FET, has now gained even more importance and taken on the dimension of safety into account as it should not simply be reduced to the basic question of effectiveness. Study design, size, duration Systematic review and meta-analysis. We registered the protocol prospectively with PROSPERO [CRD42020163086]. A literature search was performed using the following databases: EMBASE, CINAHL and MEDLINE from inception to December 2021. Inclusion criteria consisted of: (1) cohort or register based study and (2) study population of women who conceived after NC-FET and a control group of women who conceived after AC-FET. Studies including anovulatory women and women with polycystic ovary syndrome were excluded. Participants/materials, setting, methods Women who conceived after NC-FET and AC-FET. Main outcomes are birth weight, large for gestational age (LGA); macrosomia; low birth weight (LBW) and small for gestational age (SGA). Additional outcomes included: gestational diabetes (GDM), hypertensive-disorders-of-pregnancy (HDP), post-partum-hemorrhage (PPH), placenta praevia, preterm birth (PTB), very preterm birth (very PTB). We calculated pooled odds ratios (OR), adjusted ORs and prevalence estimates (95% CI) using a random effect model, while heterogeneity was assessed by the I2. Main results and the role of chance A total of 18 studies were included (NC-FET n = 45,170; AC-FET n = 50,902). Birthweight was lower following NC-FET versus AC-FET (mean difference 25.12 grams; 95% CI 10.58 – 39.96). Furthermore NC-FET compared to AC-FET resulted in a lower risk of LGA (odds ratio (OR) 0.90; 95% 0.87 – 0.94), macrosomia (OR 0.80; 95% CI 0.69 – 0.94), SGA (OR 0.92; 95% CI 0.86 – 0.99), LBW (OR 0.85; 95% CI 0.77 – 0.95), HDP (OR 0.58; 95% CI 0.48 – 0.70), PE (OR 0.45; 95% CI 0.40 – 0.51), PPH (OR 0.39; 95% CI 0.30 – 0.50), PTB (OR 0.79; 95% CI 0.72 – 0.88) and very PTB (OR 0.80; 95% CI 0.58 – 1.09). Pooled adjusted OR resulted in similar estimates. Heterogeneity was low and varied between 0% and 10%, quality of the evidence was low to moderate. Limitations, reasons for caution Protocols for per NC-FET and AC-FET varied. Several studies on NC-FET used luteal phase support (LPS) with progesterone supplementation until 10-12 weeks gestation, which could also have an effect on the obstetric and neonatal outcomes. Wider implications of the findings In combination with comparable effectiveness and considering lower risks of obstetric and neonatal complications after NC-FET: NC-FET is the preferred treatment in women with ovulatory cycles undergoing FET. Trial registration number International prospective register of systematic reviews PROSPERO CRD42020163086

P-499 Facilitators and barriers for home-based monitoring to time frozen embryo transfers in IVF

Abstract Study question What are the facilitators and barriers concerning the implementation of home-based monitoring for natural-cycle-frozen-embryo-transfer (NC-FET) from perspective of patients and healthcare providers in the Netherlands? Summary answer Most important facilitator was optimal pregnancy chance, and most important barriers were risk of missing an ovulation for patients and laboratory capacity for healthcare providers. What is known already The number of FET cycles is increasing, mainly due to improvement in laboratory techniques. Based on current evidence, there is no difference in effectiveness when NC-FET is compared to artificial-cycle-FET (AC-FET) in ovulatory women. However, NC-FET is associated with lower risk of adverse obstetric and neonatal outcomes compared with AC-FET. NC-FET is performed based on ovulation monitoring, which can be hospital-based (ultrasounds and ovulation triggering) or home-based (LH-urine-tests). Home-based-monitoring has the advantage of being the most natural protocol for FET. A systematic approach for the implementation of home-based monitoring has to start with exploring the perspectives of all stakeholders. Study design, size, duration Both patients and healthcare providers participated in the present study. A panel of experts (n = 8) hypothesised on barriers and facilitators for the implementation of home-based-monitoring during the proposal phase of the Antarctica-2 randomised controlled trial. Two different questionnaires were developed in order to investigate facilitators and barriers for patients and for health care providers. Participants/materials, setting, methods The following stakeholders participated in the study: Patients – represented by the Dutch Patient Organisation for Couples with Fertility Problems. Healthcare providers – represented by gynaecologists (Netherlands Society of Obstetrics and Gynaecology), embryologists (Dutch Federation of Clinical Embryology) and fertility doctors. Based on our power analysis we aimed for 300 completed questionnaires for the patients and a 90 completed questionnaires for the health care providers. Facilitators and barriers were analysed using frequencies, mean (SD) and ranking. Main results and the role of chance A total of 311 patients filled out the questionnaire of whom 86.8% underwent FET previously. The facilitators and barriers were ranked on a scale of 1-10 with 10 being very important. The highest priority for the patients was to implement the strategy with the highest chance of pregnancy (mean 9.7; 95% CI 9.6 – 9.7) and the lowest priority risk of missing the ovulation (mean 8.4; 95% CI 8.2 – 8.6)). A total of 96 health care providers filled out the questionnaire. According to health care providers patients would accept the strategy when it causes less interference with patients’ work and private life (mean 7.5; 95% CI 7.1 – 8.0) and with a low risk of missing the ovulation (mean 7.6; 95% CI 7.1 – 8.0). The most important facilitator for implementation of home-based monitoring for health care workers was optimising cumulative pregnancy rates (mean 8.1; 95% CI 7.7 – 8.4) and most important barrier the lack of laboratory capacity and flexibility (mean 6.4; 95% CI 5.8 – 7.0). Limitations, reasons for caution The barrier lack of laboratory capacity especially in weekends might differ between centres. We did not identify the number of centres who might experience this problem. Furthermore, these results only apply for the applicability of NC-FET in the Netherlands. Wider implications of the findings Our interpretation is that NC-FET is the preferred treatment in ovulatory women. We gained insight in the facilitators and barriers for implementation of NC-FET. Discussing results of this study with all stakeholders involved should stimulate incorporation in guidelines, especially as key professionals in guideline development took part in this study. Trial registration number The Antarctica-2 RCT (NTR: 27578) is supported by a grant of the Netherlands Organisation for Health Research and Development (ZonMw 843002807).

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