Ratio of amniotic fluid cortisol and maternal serum cortisol (AFC/MSC) as an index of fetal lung maturity.

Fifty-eight samples of amniotic fluid from pregnant women between the gestation period of 34-42 weeks were analyzed for total cortisol levels. Thirty-four simulatneous maternal serum total cortisol levels were also measured. Amniotic fluid cortisol (AFC), maternal serum cortisol (MSC) and the ratio of AFC/MSC were correlated with L/S ratio. AFC alone and AFC/MSC ratios correlate with L/S ratios (r=0.36, p less than 0.01, and r=0.46, p less than 0.01, respectively). MSC and L/S ratios had no correlation. AFC/MSC had less individual variation as compared to AFC alone. The AFC/MSC could be divided by an arbitrary line at 0.1 and values less than 0.1 signify immature fetal lungs. Values of 0.1 and greater signify mature fetal lungs.