Total and free cortisol in amniotic fluid during late pregnancy.

Total cortisol levels were measured in 81 samples of amniotic fluid obtained from 72 patients in the third trimester of pregnancy; 19 of them had pre-eclampsia and the remainder had no pre-eclampsia, hypertension or renal disease. In accordance with previous studies, there was a rise in the concentration of amniotic fluid cortisol with advancing gestation; the rise was steepest after 40 weeks, the amniotic fluid cortisol levels invariably being above 700 nmol/l between 41 and 43 weeks of pregnancy. Amniotic fluid cortisol may thus be of value in diagnosing postmaturity. A relatively low correlation was found between total cortisol levels and lecithin/sphingomyelin ratios in amniotic fluid unless results were ranked for gestational age. Total cortisol concentrations in amniotic fluid obtained from patients with pre-eclampsia were significantly higher than in controls. The concentration of free cortisol in amniotic fluid changed much less than total cortisol. Thus total cortisol should be measured in studies of the fetal capacity to synthesize corticosteroids.