Study of the pharmacokinetics of human chorionic gonadotropin and its relation to ovulation

The pharmacokinetics of human chorionic gonadotropin (hCG) was studied in 15 normal volunteers and 15 patients undergoing in vitro fertilization (IVF). Each subject received 6000 IU hCG, intramuscularly (im), at midcycle, and serum was assayed for hCG frequently for 16 hr. All 30 subjects achieved hCG concentrations greater than or equal to 10 IU/liter within 2 hr and 19 (63%) did so within 1 hr of injection. The time taken to attain concentrations of greater than or equal to 20 and greater than or equal to 40 IU/liter correlated positively with the subjects' weight and/or surface area, but the correlation was not strong. Eleven of the 15 IVF patients had oocytes retrieved 34-35 + hr post hCG. Three of the 11 showed evidence of prior "undetected ovulation" at the time of surgery (definite in one, presumed in two). Taking into consideration the pharmacokinetics of hCG and other factors that could lead to undetected ovulation, the authors conclude that (1) hCG is rapidly absorbed in the majority of subjects following im injection, (2) ovulation may occur earlier than 36 hr following hCG in some individuals, and (3) implementation of a shorter (than 35 hr) hCG-to-oocyte retrieval interval would be advised if undetected ovulation is to be avoided.