[Studies on the alteration of the unconjugated estriol level of the maternal vein after the onset of labor].

We measured maternal venous unconjugated estriol (UE3) levels in 244 cases (218 cases with labor and 26 without labor). We investigated the relationships between several obstetrical factors and UE3 levels. There was no significant difference between the group with labor and the group without labor. However, in multipara, the UE3 level fell gradually with prolonged duration of labor. There were significant positive correlations between the UE3 levels and birth weights (n = 82, r = 0.375, p less than 0.001), and placental weights (n = 82, r = 0.381, p less than 0.001) in multipara with labor. There was no significant difference according to sex between the UE3 levels of a mother carrying a male or female fetus. The UE3 levels of fetal distress cases (n = 30, mean +/- S.E. 20.0 +/- 8.6 ng/ml) were significantly (p less than 0.02) lower than those without fetal distress (n = 188, 24.5 +/- 9.7 ng/ml). These data suggest that after the onset of labor, maternal venous UE3 has some relationship to feto-placental function.