The maternal serum cortisol levels after onset of labor.

We measured maternal cortisol levels after the onset of labor. Blood from 82 primiparas and 48 multiparas were collected 124 times and 60 times, respectively. When duration of labor was within 3 hr, there were no differences in cortisol levels between the primiparous (n = 11, 50.4 +/- 7.0 micrograms/100 ml, mean +/- S.E.) and multiparous (n = 14, 37.8 +/- 4.3 micrograms/100 ml). However, when duration of labor was from 3 to 6 hr, cortisol levels in the primiparas (n = 20, 59.7 +/- 5.1 micrograms/100 ml) were significantly (p less than 0.05) higher than those in the multiparas (n = 22, 46.8 +/- 2.9 micrograms/100 ml). In cases of duration of labor from 6 to 9, cortisol level of the primiparas (n = 24, 64.3 +/- 4.4 micrograms/100 ml) were also significantly (p less than 0.05) higher than those in multiparas (n = 12, 49.4 +/- 4.7 micrograms/100 ml). When duration of labor was more than 9 hr there was no significant difference in cortisol level between the primiparas and multiparas. Maternal cortisol level had a significant (p less than 0.01) negative correlation (n = 166, r = -0.243, Y = -0.09X + 30.47) with unconjugated estriol level. These data suggest that maternal cortisol levels after the onset of labor are slightly different between the primiparous and multiparous, and that maternal unconjugated estriol levels decrease owing to reduction of the feto-placental blood circulation accompanied with uterus contraction during labor.