Cycle day, estrogen level, and lead follicle size: analysis of 27,790 in？vitro fertilization cycles to determine optimal start criteria for gonadotropin-releasing hormone antagonist - Fertility and Sterility

To determine the optimal criteria at which to start GnRH antagonists during controlled ovarian hyperstimulation (COH) for in vitro fertilization (IVF). Retrospective clinical cohort. IVF clinics. Women undergoing fresh autologous IVF using GnRH antagonist for ovulation suppression during COH. Measurement of lead follicle size, E2 level, and cycle day of stimulation on day of antagonist initiation. Clinical pregnancy rate (PR). The highest clinical PR was achieved when the antagonist was started when a lead follicle reached 14–15.9 mm in size (mean clinical PR 21.3; 95% confidence interval [CI] 19.3, 23.6) on cycle day 6 (mean clinical PR 22.2; 95% CI 17, 28.4), or when the E2 level was between 500 and 599 pg/mL (mean clinical PR 25.4; 95% CI 19.5, 32.4). Starting antagonists when the E2 level was <300 or >1,100 pg/mL reduced the odds of clinical pregnancy by 40% (odds ratio 0.60, 95% CI 0.5, 0.7). Cycle day, E2 level, and follicle size at time of antagonist start are all independent predictors of a clinical pregnancy after IVF. Initiating antagonists when the E2 level is extremely low (<300 pg/mL) or extremely high (>1,100 pg/mL) significantly reduces the odds of pregnancy.