Disappearance of exogenously administered human chorionic gonadotropin.

Concentrations of human chorionic gonadotropin (hCG) were measured after intramuscular hCG administration in 34 patients undergoing ovarian stimulation in an in vitro fertilization program. Serum hCG levels were detectable by an immunoenzymetric assay up to 14 days after injection. Individual variation in hCG concentration after injection could be minimized by expressing the daily hCG level as a fractional distribution of the value observed 36 hours after hCG administration (hCG0). In nonpregnant patients, less than 10% of the hCG0 value was found on day 10. The disappearance rate measured 36 hours after injection of hCG was exponential with a mean half-life of 2.32 days. These findings are significant for ovarian stimulation protocols, including exogenous hCG, with respect to timing and accuracy of quantitative pregnancy testing.