Gonadotropin-releasing hormone increases serum human chorionic gonadotropin in pregnant women

Hypothalamic decapeptide, gonadotropin-releasing hormone (GnRH) has been found to stimulate human chronic gonadotropin (hCG) secretion by trophoblast cells in vitro. To determine the biological effect of GnRH on the release of hCG in vivo, we studied the effect of the administration of GnRH on the serum levels of human chronic gonadotropin (hCG) during pregnancy. Serum hCG levels were measured before and 15, 30, and 60 min after the intravenous administration of 100 micrograms of GnRH to 22 volunteers with normal pregnancy. Nine of the 12 (75%) women responded to GnRH in the first trimester, while only 1 of the 5 women (20%) responded to GnRH in the second trimester. None of the 5 women tested in the third trimester showed a significant response of hCG to the injection of GnRH. The average increase in hCG during the first, second and third trimester was 160.7 +/- 13.5%, 111.0 +/- 7.4% and 95.0 +/- 2.3%, respectively (mean +/- SEM). Whereas the pregnant courses of all the cases were uneventful and normal, other abnormal pregnancies were also investigated with informed consents. Three patients with missed abortions also showed a significant response of hCG to GnRH (increase: 136.7 +/- 8.5%) when GnRH was administered before curettage of the uterine cavity. However, 4 patients with unruptured ectopic pregnancies did not respond to GnRH stimulation. These findings indicate that GnRH can stimulate the release of hCG by the placenta in vivo, consistent with the previous in vitro study, while the responsiveness depend on gestational age and the implantation site.