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