Serum human chorionic gonadotropin level after ovulation triggering is influenced by the patient's body mass index and the number of larger follicles

Objective: To identify determinants of the serum concentration of hCG levels after triggering of ovulation with exogenous hCG during controlled ovarian stimulation cycles for in vitro fertilization with or without intracytoplasmic sperm injection. Design: Retrospective cohort study. Setting: University Medical Center. Patient(s): One hundred-fifteen women who underwent conventional in vitro fertilization/intracytoplasmic sperm injection cycles from March 2003 to March 2005. Intervention(s): All patients underwent ovarian hyperstimulation with gonadotropins and GnRH-antagonist for pituitary downregulation. Patients were started on oral contraceptives 1 month before the stimulation. Gonadotropins were administered from stimulation day 1 until the day of the hCG trigger, and GnRH-antagonist was added from the day when at least one follicle reached 14 mm in diameter and continued until hCG administration. The hCG was administered in 5,000-IU, 10,000-IU, or 15,000-IU doses on the day of ovulation triggering. Main Outcome Measure(s): We performed a stepwise multiple regression analysis to predict which variable would influence the serum concentration of hCG when measured the day after the administration of exogenous hCG. Result(s): Body mass index (kg/m²) and number of follicles >14 mm were the only determinants of the hCG concentration (cumulative R² = 0.30; P<.001). Patient age, estradiol peak, number of oocytes retrieved, length of stimulation, and length of GnRH-antagonist administration in days were not associated with serum hCG levels. Conclusion(s): Knowing that the number of larger follicles and the patient's BMI are the major determinants of the hormone's clearance in the body can help in the hCG dose titration during ovarian stimulation.