Endometrial preparation for frozen-thawed embryo transfer

Abstract

Recent years have seen a rise in the number of frozen-thawed embryo transfer (FET) cycles. FET accounts for 44% of all UK in vitro fertilisation (IVF) cycles, doubling in the eight years to 2021. Despite this increase, few data exist exploring different approaches to endometrial preparation for FET.

I undertook a UK-wide survey of IVF clinics, exploring methods of endometrial preparation for FET. The results illustrate wide variation in practice. In natural cycle FET (NC-FET), clinics vary in preference for, type of and duration of supplementary progesterone. There is also variety in the time of blastocyst transfer relative to luteinising hormone (LH) surge. In medicated FET (M-FET), there is variation in duration and route of progesterone and type of ovulatory suppression.

I present the findings of a negative control study comparing blastocyst transfer on day six versus day seven after urinary LH-surge, demonstrating a doubling of the likelihood of live birth in the day six group.

During M-FET, ovulation prevention is necessary to avert an uncontrolled serum progesterone rise, which could shift the endometrial window of implantation. The optimal method of ovulatory suppression remains contentious. I analysed prospectively collected data, comparing the live birth rate of M-FET with GnRH-agonist versus GnRH-antagonist. Given the low sample size, no inferences could be drawn regarding live birth rate. However, the GnRH-antagonist FET cycle is shorter and involves less ultrasound scans and clinic visits.

I undertook a pilot RCT comparing M-FET with versus without GnRH-antagonist. The study highlights the feasibility of a full powered RCT and provides recommendations to inform design. Due to low sample size, no inferences can be made regarding the effect of GnRH-antagonist on live birth rate. However, several patients ovulated while taking oral oestradiol 6mg daily, suggesting that, at a minimum, monitoring for ovulation should be undertaken during M-FET.

Date of Award	1 Oct 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	David Cahill (Supervisor) & Debbie A Lawlor (Supervisor)