Fetal Responses to Glucocorticoids

This chapter focuses primarily on the 30 years of often conflicting responses of intact fetuses to glucocorticoid exposure following Liggins' observation in 1969 that antenatal glucocorticoids induced early lung maturation in preterm sheep (1). Although the emphasis is on the surfactant system, other effects of glucocorticoid treatments on the fetal lung need to be discussed to dissociate them from effects on the surfactant system. The use of antenatal glucocorticoids is now routine for fetuses at risk of preterm delivery (2). A clinical perspective on the efficacy of antenatal glucocorticoids in humans is useful to focus the interpretation of the experimental data on the important clinical questions. Following the initial randomized controlled clinical trial of antenatal betamethasone to decrease the incidence of respiratory distress syndrome (RDS) published in 1972 (3), 14 other randomized and controlled trials were included in a metaanalysis in 1995 (2). Antenatal glucocorticoids decrease the incidence of RDS and death by about 50%. The benefits seem to occur at very early gestational ages, but there are limited clinical data on this point. There may be benefit for glucocorticoid treatment to delivery intervals of less than 24 h, although the 0-to 24-h interval has not been examined as to the minimal interval for effects on the incidence of RDS. There are minimal data suggesting that the beneficial effects of antenatal glucocorticoids may be lost if the treatment to delivery interval extends beyond 7 to 10 d (4) . Although repetitive courses of antenatal glucocorticoids are frequently used, there are no randomized and controlled trials evaluating the safety or efficacy of this approach. Fetal Responses to Glucocorticoids