Optimizing the protocol for modified natural cycle frozen embryo transfer (mNC-FET): a multicentre, single-blinded...

Area of Science:

• Reproductive Endocrinology and Infertility
• Assisted Reproductive Technologies (ART)
• Embryology and Embryo Transfer

Background:

• Modified natural cycle frozen-thawed embryo transfer (mNC-FET) commonly involves luteal phase support (LPS) and blastocyst transfer 7 days post-hCG trigger.
• Evidence supporting the routine use of progesterone LPS in mNC-FET is limited.
• Optimal timing for blastocyst transfer in mNC-FET remains an area of investigation.

Purpose of the Study:

• To investigate if progesterone luteal phase support (LPS) improves live birth rates (LBR) in modified natural cycle frozen-thawed embryo transfer (mNC-FET).
• To determine if advancing blastocyst transfer to day 6 versus day 7 post-hCG trigger enhances LBR in mNC-FET.
• To evaluate the combined effect of LPS and transfer timing on LBR in mNC-FET.

Main Methods:

• A multicentre, single-blinded, randomized controlled superiority trial involving 602 women undergoing mNC-FET with a single autologous blastocyst.
• Participants were randomized to four groups: transfer on day 6 with LPS, day 7 with LPS, day 6 without LPS, or day 7 without LPS.
• Women aged 18-41 years from eight public fertility clinics in Denmark were included.

Main Results:

• The use of LPS did not significantly affect the LBR (34.9% with LPS vs. 31.9% without LPS; P=0.39).
• There was no significant difference in LBR between blastocyst transfer on day 6 versus day 7 (33.8% vs. 33.0%; P=0.87).
• The study found no significant improvement in LBR with either progesterone LPS or advanced blastocyst transfer timing in mNC-FET.

Conclusions:

• Supplementary progesterone does not appear to improve live birth rates in mNC-FET.
• Flexibility in scheduling blastocyst transfers (day 6 vs. day 7) is feasible for most women undergoing mNC-FET.
• Findings suggest a less restricted approach to FET may be possible, potentially reducing patient burden and costs without compromising success rates.