The future of frozen-thawed embryo transfer in hormone replacement therapy cycles

Abstract

Purpose of reviewThis review focuses on the efficacy of letrozole stimulated frozen-thawed embryo transfer (FET) compared to hormone replacement therapy (HRT) FET in women with polycystic ovarian syndrome (PCOS) and/or oligoanovulation. Further, obstetric and perinatal risks in HRT FET are summarized. Recent findingsThe presence of a corpus luteum seems to reduce the risk of pregnancy-related hypertension and preeclampsia after FET. As a natural cycle (NC) FET is not an option for women with oligo-/amenorrhea these women may benefit from FET with mild stimulation compared to HRT FET. The intention of mild stimulation in anovulatory women is to induce (mono) ovulation to mimic the endocrine profiles of the natural cycle and the early pregnancy after natural conception. Mild stimulation by letrozole is patient friendly and cheap compared to gonadotropin stimulated FET and has been increasingly used in recent years. Although the quality of evidence is low, the pregnancy outcomes after letrozole FET seems similar or even better compared to HRT FET in women with PCOS and/or oligo-anovulation. SummaryNatural and modified NC FET should be used whenever possible to mitigate adverse obstetric and perinatal outcomes after HRT FET. For anovulatory women, whenever ovulation can be induced, we advocate the use of mild stimulation FET to create a corpus luteum awaiting results from RCTs limited to oligo-anovulatory women.

Ideal frozen embryo transfer regime

“…It is now well established that whenever a functional corpus luteum can be created (either in a natural ovulatory cycle, or with the help of medical intervention), the artificial FET cycle is not recommended [3 ▪ ,4 ▪ ,5 ▪ ]. However, still, we occasionally care for patients who cannot achieve ovulation by any means (mostly menopausal women), and for whom the only way to achieve pregnancy is by the artificial FET cycle.…”