Glucocorticoid levels in maternal and cord serum after prenatal betamethasone therapy to prevent respiratory distress syndrome.

Serum glucocorticoid levels were determined in 20 mothers and 43 premature infants who received prenatal betamethasone therapy for prevention of respiratory distress syndrome (RDS). Maternal betamethasone peaked at 75 microg cortisol equivalents per 100 ml 1 h after injection of 12 mg steroid and declined to half by 6 h. Betamethasone in cord blood was 14.3 microg cortisol equivalents per 100 ml at 1 h, decreased to a level of 4.7 at 20 h, and was not detected 2 days after a second dose at 24 h. After the second dose, the mean level of cortisol in cord blood was 5.9 microg per 100 ml compared with 13.05 microg per 100 ml (p less than 0.001) in untreated premature infants. The unbound glucocorticoid activity in treated infants delivered 1-10 h after the second dose (mean, 8.4 microg per 100 ml) is similar to the unbound cortisol level after birth in untreated premature infants who develop RDS. These findings indicate that (a) serum glucocorticoid levels in the physiologic stress range can induce lung maturation in the human and (b) antenatal treatment with this dose of betamethasone does not expose the human fetus to potentially harmful pharmacologic levels of steroid.