Objective: To determine serum E2 and P levels around the time of implantation in normal and high IVF responders.

Setting: In Vitro Fertilization program at the Instituto Valenciano de Infertilidad.

Patients: Twenty-nine women undergoing IVF, who accepted to be studied daily, were classified according to the number of oocytes retrieved in normal (n = 16) and high responders (n = 13).

Design: Prospective study in which blood was drawn daily from the day of hCG administration (day 0) up to 7 days later (day 6).

Main outcome measurements: In vitro fertilization parameters (number of ampules, FSH-hMG, number of oocytes, fertilization rates, number of transferred embryos, implantation rates, and pregnancy rates); serum E2 and P levels during the 7 days of the study.

Results: Implantation rate was significantly higher in normal (18.5%) as compared with high (0%) responders. Estradiol and P levels were elevated significantly in high responders. The E2:P ratio was significantly different between normal and high responders during the preimplantation period. Pregnancy and implantation rates decreased as serum E2 levels increased on days 4 to 6 of the study.

Conclusions: A different endocrine milieu between normal and high responders is detected by daily steroid measurements up to the preimplantation period, suggesting that this difference could be responsible for an impaired implantation in high responder patients undergoing IVF. An increase in serum E2 levels seems to be the cause of this difference.