Estradiol on trigger day: Irrelevant to live birth rates of fresh cycles but positively associated with cumulative live birth rates

Objective: To assess the effects of estradiol (E2) on trigger day on cumulative live birth rates (CLBRs), and pregnancy outcomes after fresh and frozen–thawed embryo transfer (FET). Methods: This multicenter retrospective cohort study included 42 315 patients from five reproductive centers. Six subgroups were divided according to E2 on trigger day (<1000, 1000–2000, 2000–3000, 3000–4000, 4000–5000, >5000 pg/mL). Smooth curve fitting and nonlinear mixed-effects models were used. Results: When E2 was <5500 pg/mL, the CLBR increased by 10% for every 1000 pg/mL increase in E2. When E2 was between 5500 and 13 281 pg/mL, CLBR increased by 1.8% for every 1000 pg/mL increase in E2. When E2 was >13 281 pg/mL, CLBR decreased by 3% for every 1000 pg/mL increase in E2. From group E2 < 1000 to group E2 > 5000 pg/mL, pregnancy and live birth rates in fresh cycles were not related to E2. The live birth rate after FET was higher in the E2 ≥ 5000 pg/mL group than in the E2 < 1000 pg/mL group (odds ratio [OR] 4.03, and 95% confidence interval [CI] 3.74–4.35; adjusted OR 1.20, 95% CI 1.05–1.37). Conclusion: CLBR is associated with E2 on trigger day in a segmented manner. Pregnancy and live birth rates in fresh cycles were not associated with E2. The live birth rate in FET cycles was highest when E2 ≥ 5000 pg/mL.