Retrograde time-scale analysis of human placental lactogen, beta human chorionic gonadotropin, and unconjugated estriol levels in human maternal serum from the onset of spontaneous labor.

We analyzed on a retrograde time scale which calculated in maternal serum, from the onset of spontaneous labor, human placental lactogen (hPL), beta human chorionic gonadotropin (beta-hCG), unconjugated estriol (E3) levels, and the ratios among these hormones in the normal late pregnancy. Maternal serum hPL, beta-hCG, and unconjugated E3 levels were measured simultaneously and serially in regular menstrual sera from 27 women in late pregnancy (total 155 samples) by radioimmunoassay. The peak level of hPL was found at 2 weeks before labor, and the peak of beta-hCG was found during 2-4 weeks before the onset of spontaneous labor. On the other hand, the mean level of E3 rose slightly with advancing gestational age. The hormonal ratios of hPL to E3 and beta-hCG to E3 decreased gradually toward the onset of labor, but the ratios of hPL to beta-hCG did not change. From these data, it is possible to conclude that the onset of spontaneous labor can be predicted by measuring the levels of hPL and unconjugated E3 in maternal peripheral serum.