PREGNANCY OUTCOMES IN LETROZOLE OVULATION INDUCTION FROZEN-THAWED EMBRYO TRANSFER CYCLES AS COMPARED TO NATURAL AND PROGRAMMED CYCLES

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The optimal endometrial preparation for frozen-thawed embryo transfer (FET) cycles is controversial and variable among IVF centers. Our aim is to compare pregnancy outcomes between letrozole ovulation induction FET cycles, natural FET cycles and programmed FET cycles in a US-based population. Single academic center retrospective cohort study. 2310 cycles consisting of patients <43 years utilizing embryos created from autologous oocytes between 2015-2020 were included. Blastocyst embryo transfer occurred 6 days after a natural LH surge to >20 mIU/mL in natural and letrozole cycles, or 6 days after the initiation of intramuscular progesterone in programmed cycles. The primary outcome was the ongoing pregnancy rate (OPR), and secondary outcomes included pregnancy rate (PR), implantation rate (IR), clinical pregnancy rate (CPR), and clinical loss rate (CLR). Chi-square test for categorical data and one-way ANOVA for continuous data was used with Bonferroni correction for multiple comparisons. Multiple logistic regression analysis was performed adjusting for age, BMI, anovulation diagnosis, number of embryos transferred and utilization of preimplantation genetic testing for aneuploidy (PGT-A). A two-sided p-value of <0.05 was considered statistically significant. There was a higher proportion of patients with a diagnosis of anovulation in both letrozole and programmed FET cycles compared with natural cycles (p < 0.01). Patients undergoing programmed FET cycles were more likely to be younger, have a higher BMI, and to have more embryos transferred compared to patients undergoing natural FET and letrozole FET cycles (p < 0.01). The OPRs and CPRs were similar between the groups, while the CLRs were higher in the programmed compared with natural and letrozole FET cycles. After adjusting for potential covariates, the probability of clinical loss was still significantly higher in programmed cycles compared with natural and letrozole FET cycles (aOR 1.58; 95% CI, 1.15-2.12; p < 0.01).Tabled 1OutcomeNatural FET (n = 1135)Letrozole FET (n = 88)Programmed FET (n = 1087)p valuePR (%, n)77.8 (883/1135)78.4 (69/88)79.9 (869/1087)0.46IR (%, n)62.1 (877/1413)63.4 (64/101)62.1 (903/1455)0.96CPR (%, n)68.8 (781/1135)67.0 (59/88)69.5 (755/1087)0.87OPR (%, n)60.4 (686/1135)59.1 (52/88)56.9 (619/1087)0.25CLR (%, n)11.5 (90/781)11.9 (7/59)17.5 (132/755)<0.01 Open table in a new tab Letrozole ovulation induction may be a better alternative to programmed FET cycles particularly for anovulatory patients in view of the lower clinical loss rate.