Evidence for a local change in the progesterone/estrogen ratio in human parturition at term.

The purpose of this study was to determine if a local change in the concentrations of estrogen and progesterone occurs in the amniotic fluid during human parturition at term. Amniotic fluid was retrieved from 20 women in active labor and from 20 women not in labor. Patients were matched for maternal age and gestational age. Estradiol, estriol, progesterone, and dehydroepiandrosterone sulfate were measured in amniotic fluid by radioimmunoassay. For women in active labor, the median concentrations (range) of these steroid hormones were 2.4 ng/ml (1 to 9.2 ng/ml), 1661.2 ng/ml (556.6 to 3928.1 ng/ml), 12.3 ng/ml (4.7 to 41.4 ng/ml), and 187.5 ng/ml (61.2 to 470 ng/ml), respectively. The median concentrations (range) for women not in labor were 1.6 ng/ml (0.3 to 5.7 ng/ml), 684.2 ng/ml (70.6 to 2103.1 ng/ml), 13.2 ng/ml (7.5 to 63 ng/ml), and 65.6 ng/ml (20 to 334 ng/ml), respectively. Thus spontaneous human parturition at term was associated with significantly increased amniotic fluid concentrations of estradiol, estriol, and dehydroepiandrosterone sulfate (p = 0.02, p = 0.002, p = 0.003, respectively). The progesterone/estrogen ratios (progesterone/estradiol and progesterone/estriol) were significantly lower for women in active labor compared with those not in labor (p = 0.002 and p = 0.0006, respectively). We conclude that a local change in the progesterone/estrogen ratio occurs during human parturition at term.