The absorption by the human fetus of intra-amniotically injected cortisol

The absorption of cortisol from amniotic fluid by mother and fetus is poorly understood. Clarification is desirable since the amniotic route might serve as the optimal means of administering glucocorticoids and other drugs to the fetus when this is warranted. To gain some idea of the extent of the fetal absorption of cortisol, tritiated cortisol was injected intra-amniotically 20 min prior to delivery of four fetuses from 11 to 21 weeks gestational age. The tissues were analyzed for cortisol and some of its unconjugated metabolites. The placenta contained about 4% and the fetus 2% of the injected dose, the bulk of the radioactivity remaining in the amniotic fluid. Cord serum levels of radioactivity varied from 2.8 to 9.3% of the amniotic fluid level. Considerable conversion to cortisone had occurred in many tissues, particularly the placenta, lung and kidney. These results suggest that intra-amniotic injection may provide an efficient means of supplying glucocorticoids to the human fetus.