High serum estradiol levels on the day of frozen blastocyst transfer are associated with increased early miscarriage rates in artificial cycles using transdermal estrogens.

This article investigates the impact of serum estradiol (E2) levels on the day of frozen blastocyst transfer (FBT) in hormonal replacement therapy (HRT) cycles using transdermal estrogens on pregnancy outcomes. In a retrospective cohort of 2,364 patients undergoing single autologous FBT with transdermal E2 and vaginal progesterone, E2 levels ≥313 pg/ml were associated with a significantly increased early miscarriage rate (EMR) but showed no significant effect on live birth rate (LBR) or neonatal outcomes. The study highlights that while elevated E2 may impair early pregnancy maintenance, it does not appear to reduce overall live birth success in this context. Limitations include its retrospective design and lack of embryo aneuploidy screening, and the findings are specific to HRT cycles with transdermal estrogen, suggesting a need for further research to define optimal E2 thresholds and personalize treatment protocols.