OBJECTIVE: To compare the impact of elevated P during the late follicular phase on the chance of pregnancy in low, normal, and high responders.DESIGN: Retrospective combined analysis from six clinical trials.SETTING: IVF centers.PATIENT(S): Women up to 39 years of age with a regular menstrual cycle and an indication for ovarian stimulation before IVF/intracytoplasmic sperm injection.INTERVENTION(S): Ovarian stimulation with recombinant (r) FSH in a GnRH antagonist protocol.MAIN OUTCOME MEASURE(S): Ongoing pregnancy rates (OPRs) assessed with the use of univariate and multivariate analyses according to serum P levels ≤ 1.5 ng/mL versus >1.5 ng/mL on the day of hCG administration and compared among low (1-5 oocytes), normal (6-18 oocytes), and high (>18 oocytes) responders.RESULT(S): A total of 157/1,866 women (8.4%; 95% confidence interval [CI] 7.2%-9.8%) had elevated P. Incidence of elevated P increased from 4.5% in low responders to 19.0% in high responders. Overall, OPRs were significantly lower in women with elevated P. Per started cycle, the >1.5 to ≤ 1.5 ng/mL adjusted odds ratio was 0.55 (95% CI 0.37-0.81). OPRs were not impaired in high responders with P elevation and were significantly higher compared with normal responders with P elevation.CONCLUSION(S): The incidence of elevated P increases with ovarian response, and elevated P at a threshold of 1.5 ng/mL is independently associated with a decreased chance of pregnancy in low to normal responders, but not in high responders, when using an rFSH/GnRH antagonist protocol.