LAUSR

The underlying mechanism for an ectopic pregnancy (EP) following an intrauterine embryo transfer is not fully understood. While ectopic pregnancies result from alterations in the tubal environment in most natural cycles, endometrial receptivity is the primary concern following in vitro fertilization (IVF). Elevations in estradiol and progesterone levels during controlled ovarian stimulation (COS) are associated with morphological changes in the endometrium that may augment or interfere with normal implantation. Perhaps as a result of the exaggerated hormonal environment resulting from IVF stimulation, the risk of EP has been shown to be greater during a fresh compared to frozen embryo transfer (ET) cycle. However, despite lower steroid hormone levels in a frozen ET cycle, ectopic risk is still higher than in natural cycles. This study aimed to determine whether estradiol (E2) and progesterone (P4) levels during a frozen, blastocyst ET cycles are associated with EP risk.