Antenatal steroids and the developing brain

Randomised clinical trials show that two injections of corticosteroid into the mother before preterm delivery reduce respiratory distress syndrome, ne onatal mortality, and intraventricular haemorrhage. However, repeated cours es of antenatal steroid are not backed by such evidence of safety and effic acy. Animal studies have shown that maternal corticosteroid delays myelinat ion and reduces the growth of all fetal brain areas particularly the hippoc ampus. Corticosteroids may reduce or enhance hypoxic-ischaemic injury to th e developing brain depending on timing and dosage. Clinical trials of mater nally administered corticosteroid show no evidence of increased disability on follow up but numbers are small. Postnatal trials of dexamethasone when brain maturity is still preterm show a significant increase in later disabi lity in the dexamethasone treated groups. There is evidence from randomised trials, retrospective data, experiments on pregnant mice, and the chemical make up of the preparations that betamethasone may be safer and more prote ctive of the immature brain than dexamethasone. Single course corticosteroi d treatment before preterm delivery must still be recommended as a life sav ing and cost effective intervention, but clinicians may wish to change from using dexamethasone to betamethasone. In view of the animal and postnatal data, clinicians should be cautious with repeated courses of antenatal cort icosteroids and repetition may be unnecessary for lung maturity.