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

Study Question: Do serum estradiol (E2) levels on the day of frozen blastocyst transfer (FBT) affect pregnancy outcomes in hormonal replacement therapy (HRT) cycles using transdermal estrogens?

Summary Answer: E2 levels ≥313 pg/ml on the day of FBT are associated with increased early miscarriage rates (EMRs), but do not significantly impact the live birth rate (LBR).

What Is Known Already: E2 plays a crucial role in endometrial receptivity and placentation. The effect of serum E2 levels measured around the time of FBT in HRT cycles remains debated, with some studies indicating a negative impact of high E2 levels and others finding no significant difference.