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 (E 2 ) 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: E 2 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 E 2 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 (≥ 17 mm). The follicular lots were analyzed retrospectively and a MRE was determined. In a later prospective study, plasma E 2 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 E 2 levels as a function of follicular diameter: MRE of E 2 (pg/ml) = 556 + 95 A + 98 B + 108 C. In the prospective study, the correlation coefficient for the measurements of E 2 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 E 2 levels in stimulated ovarian cycles.