Impact of different progesterone timings on live birth rates for blastocyst frozen embryo transfer cycles.

RESEARCH QUESTION: Do different timings of progesterone administration for day 5 and day 6 blastocysts affect the live birth rate (LBR) of artificial frozen embryo transfer (FET) cycles? DESIGN: This retrospective cohort study included 1362 patients who underwent artificial FET cycles. The effects of 6 and 7 days of progesterone administration prior to blastocyst transfer on clinical outcomes were compared in day 5 and day 6 blastocysts. Univariable and multivariable regression analyses were undertaken. RESULTS: In all patients, LBR was comparable between the two groups (51.8% versus 47.9%, P = 0.165). For day 6 blastocysts, after adjusting for confounders, the 7-day progesterone regimen resulted in a significantly higher LBR (44.8% versus 36.4%, P = 0.039, adjusted OR = 1.494, 95% CI 1.060-2.106) and lower pregnancy loss rate (15.4% versus 25.2%, P = 0.031, adjusted OR = 0.472, 95% CI 0.260-0.856) compared with the 6-day progesterone regimen. For day 5 blastocysts, there were no significant differences in pregnancy outcomes between the two regimens, but the rate of low birthweight was higher with the 7-day progesterone regimen than with the 6-day progesterone regimen (13.9% versus 6.7%, P = 0.032). CONCLUSIONS: In all blastocyst analyses, no difference in LBR was found between the 6- and 7-day progesterone regimens in artificial FET cycles. For day 6 blastocysts, LBR was significantly higher with the 7-day progesterone regimen than with the 6-day progesterone regimen, whereas for day 5 blastocysts, pregnancy outcomes were comparable between the two regimens.