The efficiency of human reproduction after in vitro fertilization and embryo transfer.

Two hundred ninety-seven nonpregnant patients were used to study the possibility of early transient implantation as a parameter of the efficiency of in vitro fertilization (IVF) procedures. Ten patients without embryo transfer (ET) were used as controls. The luteal estradiol, progesterone, and human chorionic gonadotropin were measured by radioimmunoassay (RIA). In 31 cases, a transient elevation of hCG occurred after complete serum clearance of exogenous hCG, suggesting that the transient increase in hCG was of embryonic origin. In addition, five patients were found to have prolonged clearance of hCG, which was due not to individual variation in clearance, but to a minimal production of hCG by trophoblastic tissue. These data suggest that implantations occurred in 12.1% of our so-called "nonpregnant" patients.