As part of a series of studies on the endocrine consequences of corticosteroid treatment during late pregnancy, the levels of unconjugated estrone (E1), estradiol-17β (E2), and progesterone were followed in maternal plasma and amniotic fluid before and after treatment. Ten gravidas in the 30th-35th gestational week received 12 mg betamethasone daily for 3 days for prevention of idiopathic respiratory distress syndrome (IRDS) and were compared to S controls. The steroid concentrations were determined by radioimmunoassay. The plasma levels of E1 and E2 were depressed to 38% and 29%, respectively, while that of progesterone was not affected. No significant change of the steroid concentrations in amniotic fluid was observed. The decreased E2: progesterone ratio in maternal blood after betamethasone treatment in the human is in contrast to the increased ratio observed in ruminants after corticosteroid administration and preceding the spontaneous onset of labor. The fall in the E2: progesterone ratio accords with the earlier observed inability of intramuscular corticosteroid treatment of elicit labor in women at this stage of gestation. The earlier demonstrated marked depression of cortisol in fetal plasma after betamethasone seems paradoxical in view of the seemingly high availability of progesterone, considered as a precursor for the cortisol biosynthesis in the human fetal adrenal cortex.
© 1977 The American College of Obstetricians and Gynecologists