Fetal lung maturation. III. The amniotic fluid cortisol/cortisone ratio in preterm human delivery and the risk of respiratory distress syndrome.

Cortisol and cortisone have been measured in amniotic fluid samples obtained within 24 hours of deliver of 50 premature infants. When expressed as cortisol/cortisone ratios, the ratio tends to rise with advancing gestational age, although statistical significance is not attained. Both cortisol concentration and the cortisol/cortisone ratio are significantly lower in the amniotic fluid of infants who develop respiratory distress syndrome than in those with mature lung function (cortisol ratio: 19.2 +/- 10.3 ng/ml vs 26.1 +/- 9.4, P less than .02; cortisol/cortisone ratio: 1.2 +/- 0.6 vs 2.0 +/- 0.8, P less than .001). These findings also hold in the subgroup of infants less than 32 weeks' gestation but not in those infants at or beyond the 32nd week. The amniotic fluid cortisone concentration is significantly lower in infants born after spontaneous labor beginning with rupture of the membranes as opposed to after contractions or bleeding (13.2 +/- 3.6 ng/ml vs 16.3 +/- 6.1, P less than .05), although the cortisol concentrations and the cortisol/cortisone ratios are not significantly different.