P-542 How should we prepare the endometrium in euploid embryo transfer cycles? Modified natural or artificial endometrial preparation?

Abstract Study question Does modified natural endometrial preparation in single euploid frozen-thawed embryo transfer (FET) cycles affect chance of pregnancy and risk miscarriage compared to artificial? Summary answer The rate clinical live birth increases while the decreases FET artificial cycles. What is known already Corpus luteum produces growth factors, angiogenic factors vasoactive substances as well hormones. These play role for initial placentation. Early maternal endocrine milieu resulting exogenous estrogen progesterone could damage placentation, which may turn cause miscarriage. High estradiol levels might also be responsible decreased rates (Wu et al 2021). design, size, duration This retrospective, center study evaluated 1890 frozen women between 20-43 years old from January 2017 September 2021. based on data obtained Istanbul Memorial Hospital, ART Reproductive Genetics Center. were analyzed two groups according different protocol. Group A (n = 1335): (mNat/FET) B 555): (AC-FET). Participants/materials, setting, methods Only good prognosis patients with ages included. Exclusion criterias age 44 above, recurrent abortion history, BMI>35 kg/m 2, factor, uterin factor (adenomyosis, mullerian anomaly) history. NGS was used trophoectoderm biopsy material all cases. Patients demographics, cycle characteristics outcomes analyzed. Main results We effect after excluding confounding There no significant differences patient demographics such age, body-mass index, infertility duration, previous IVF attempts, AMH level, daily gonadotropin dosage used, number oocytes obtained, mature fertilized groups. difference morphologic grading transferred embryos both However, statistically significantly In group A, biochemical (76.9% vs. 73.9%, p:0.04), (71% 65.7%, p < 0.01), (65.4% 50.5%, 0.01) higher than B. Also, loss (7.7% 11%, p:0.01), (6.7% 21%, second trimester (0.8% 1.5%, p:0.04) lower Limitations, reasons caution limitation our include fact that this a retrospective analysis. Prospective randomised studies are necessary evaluate outcomes. Wider implications findings shows better undergoing mNat/FET even controlling when comparing AC-FET As result, appropriate patients, should preferred much feasible. Trial registration Not applicable