Betamethasone and the rhesus fetus: multisystemic effects.

In this controlled study of betamethasone administration to pregnant rhesus monkeys, using dosages per gram of fetal body weight similar to those reported in several human clinical studies, the most significant fetal pulmonary changes observed were increases in maximum lung volumes. The fact that comparable increases in peak volumes were demonstrated on saline filling supports our contention that these changes are related primarily to lung structural alterations rather than surfactant effects. Additional findings in the treated animals included reduced fetal head circumference, thymus weight, adrenal weight, placental weight, and maternal postoperative weight and increased fetal hepatic weight. Any of these glucocorticoid-induced changes could portend serious side effects. Further studies are needed to delineate the risk:benefit ratio of such treatment.