Calculation of plasma estradiol levels by analysis of number and size of follicles measured by ultrasound.

OBJECTIVE To determine the possibility of immediate estimation of plasma estradiol (E2) levels in stimulated ovarian cycles using a multiple regression equation (MRE) based on the analysis of the number and size of ovarian follicles measured by pelvic ultrasound. METHOD E2 levels were measured by enzyme immunoassay (EIA) in 47 patients on the day of induction of ovulation with human chorionic gonadotropin (hCG). MRE was employed to calculate E2 levels after analysis of the number of follicles present, divided into three groups according to their greatest ultrasonic diameters A (10-14 mm), B (15-16 mm) and C (> or = 17 mm). The follicular lots were analyzed retrospectively and a MRE was determined. In a later prospective study, plasma E2 levels were measured by EIA and MRE in 36 patients on the day of induction of ovulation with hCG. RESULTS The following MRE was obtained for plasma E2 levels as a function of follicular diameter: MRE of E2 (pg/ml) = 556 + 95 A + 98 B + 108 C. In the prospective study, the correlation coefficient for the measurements of E2 levels by the two methods (EIA versus MRE) was 0.70. CONCLUSION The use of MRE based on the analysis of number and size of ovarian follicles measured by ultrasound permits a relatively precise indirect estimate of plasma E2 levels in stimulated ovarian cycles.