Pregnancy outcomes after frozen-thawed embryo transfer using letrozole ovulation induction, natural, or programmed cycles

To evaluate and compare pregnancy outcomes between letrozole ovulation induction, natural, and programmed frozen-thawed embryo transfer (FET) cycles in a population based in the United States.Retrospective cohort study.Single university-affiliated infertility practice.A total of 3,148 FET cycles consisting of patients aged ≤45 years transferring blastocysts that were created from autologous oocytes between January 2015 and July 2021.None.The primary outcome was the ongoing pregnancy rate (OPR) or live birth rate (LBR). The secondary outcomes included clinical pregnancy and clinical loss rates (CLRs).The OPR/LBR was higher among letrozole FETs than among programmed FETs (adjusted risk ratio [aRR] 1.11, 95% confidence interval [CI] 1.02-1.21) but comparable to natural FETs (aRR 1.05, 95% CI 0.96-1.14). The OPR/LBR was comparable between natural and programmed FETs (aRR 1.06, 95% CI 0.99-1.13). The CLR was lower in the natural FET group than in the programmed FET group (aRR 0.62, 95% CI 0.46-0.84). There were no differences in CLRs between letrozole and programmed FETs and between letrozole and natural FETs. Among ovulatory women, the OPR/LBR among letrozole FETs was higher than that among programmed FETs (aRR 1.16, 95% CI 1.05-1.28). The CLR among ovulatory women was significantly lower in both letrozole FETs (aRR 0.44, 95% CI 0.22-0.87) and natural FETs (aRR 0.59, 95% CI 0.43-0.80) than in programmed FETs. Among anovulatory women, the OPR/LBR in the letrozole FET group was similar to that in the programmed FET group (aRR 0.95, 95% CI 0.79-1.13).Letrozole and natural FET clinical outcomes were improved compared with programmed FET outcomes.