Effect of betamethasone in vivo on placental corticotropin-releasing hormone in human pregnancy

The objective was to determine the effects of in vivo administration of prenatal betamethasone in patients at 26 to 35 weeks' gestation on corticotropin-releasing hormone concentrations in maternal and fetal plasma and amniotic fluid, and on corticotropin-releasing hormone localization in placenta and fetal membranes. A total of 49 pregnant women at risk for preterm delivery between 26 and 35 weeks' gestation were studied. Twenty-six patients received betamethasone (12 mg intramuscularly) for stimulation of fetal lung maturity. Cord blood, amniotic fluid, placental tissue, and fetal membranes were obtained from 22 of these patients at delivery by elective cesarean section at 33.8+/-2.4 weeks' gestation. In control patients (n=23) at comparable gestational age, blood samples were taken for hormone analysis (n=8), and cord blood, amniotic fluid, and tissues were collected at elective cesarean section at 34.1+/-2.3 weeks' gestation. Concentrations of corticotropin-releasing hormone, adrenocorticotropic hormone, and cortisol were determined by radioimmunoassay. Localization of tissue immunoreactive corticotropin-releasing hormone was assessed by immunohistochemistry. Betamethasone caused approximately 90% reduction in maternal cortisol and 50% reduction in maternal plasma adrenocorticotropic hormone. In patients at >30 weeks' gestation, there was a significant increase in maternal plasma corticotropin-releasing hormone concentrations after betamethasone; maternal corticotropin-releasing hormone was not altered significantly in untreated patients. Corticotropin-releasing hormone levels were raised in umbilical cord blood by 48 hours and in amniotic fluid 1 week after betamethasone administration. There was increased immunohistochemical staining for corticotropin-releasing hormone in placental syncytiotrophoblast and in fetal membranes of patients treated with betamethasone. These studies provide the first evidence for in vivo stimulation of plasma corticotropin-releasing hormone, likely of placental origin, by glucocorticoids in third trimester human pregnancy. The results suggest that increases in endogenous cortisol during normal gestation may contribute to placental corticotropin-releasing hormone output and to the rise in maternal plasma corticotropin-releasing hormone concentrations during late pregnancy.