Modified natural and optimized programmed frozen embryo transfers have equivalent live birth rates: an analysis of 6,682 cycles.

OBJECTIVE: To compare the live birth rates (LBRs) in modified natural and programmed single blastocyst frozen embryo transfer (FET) cycles. DESIGN: Retrospective cohort study. SETTING: University-affiliated fertility practice. PATIENT(S): Patients who underwent single blastocyst FETs between January 2014 and December 2019. A total of 15,034 FET cycles from 9,092 patients were reviewed; 1,186 modified natural and 5,496 programmed FET cycles from 4,532 patients met the inclusion criteria for analysis. INTERVENTION(S): No intervention. MAIN OUTCOME MEASURE(S): The primary outcome measure was the LBR. RESULT(S): There was no difference in live birth after programmed cycles using intramuscular (IM) progesterone or a combination of vaginal progesterone and IM progesterone compared with that after modified natural cycles (adjusted relative risks, 0.94 [95% confidence interval {CI}, 0.85-1.04] and 0.91 [95% CI, 0.82-1.02], respectively). The relative risk of live birth decreased in programmed cycles that used exclusively vaginal progesterone compared with that in modified natural cycles (adjusted relative risk, 0.77 [95% CI, 0.69-0.86]). CONCLUSION(S): The LBR decreased in programmed cycles that used only vaginal progesterone. However, no difference in the LBRs existed between modified natural and programmed cycles if programmed cycles used either IM progesterone or a combination of IM and vaginal progesterone protocols. This study demonstrates that modified natural FET cycles and optimized programmed FET cycles have equivalent LBRs.