Background: The purpose of this prospective observational study was to evaluate the association between estradiol (E(2)) levels on the day of human chorionic gonadotrophin (hCG) administration and pregnancy rates in a recombinant FSH (rec-FSH) antagonist fixed protocol.
Methods: A group of 207 patients (<or=39 years of age), treated by IVF/ICSI, received 200 IU/day rec-FSH from Day 2 of the cycle and daily GnRH antagonist starting on Day 6 of stimulation. The criteria for hCG administration included only the presence of >or=3 follicles of >or=17 mm diameter. One to two embryos were transferred on Day 3 after oocyte retrieval.
Results: The area under the curve (AUC) for E(2) on the day of hCG could not distinguish between pregnant and non-pregnant women (AUC:0.5; 95% confidence interval (CI): 0.42-0.59). No significant difference was observed between the three percentile groups of E(2) values on the day of hCG administration [group 1, lower 25th percentile (<1142 pg/ml); group 2, medium 50th percentile (1142-2446 pg/ml) and group 3, higher 75th percentile (>2446 pg/ml)] for the ongoing pregnancy rates (P = 0.52). On the contrary, the linear regression model showed that higher E(2) values on the day of hCG administration significantly improved the scores of transferred embryos (P = 0.01) as well as the total embryo score (P = 0.02). Yet subgroup analysis only in this high responders group revealed lower E(2) and progesterone levels on the day of hCG in pregnant women compared with the non-pregnant (P = 0.01).
Conclusions: E(2) concentrations on the day of hCG administration in GnRH antagonist cycles are not associated with pregnancy rates. A potential deleterious impact of estradiol on endometrial receptivity is shown for the high responders who have high E(2) levels and improved embryo quality without a concomitant rise in pregnancy rate.