In pregnancy, pharmacokinetics of corticosteroids changes. Systemic corticosteroids are not teratogenic. Pregnant women receiving corticosteroid therapy suffer the same side effects and benefits as do treated women who are not pregnant. Clinical experience suggests no abnormalities of children of mothers treated with usual doses of prednisone and methylprednisolone throughout pregnancy, but premature rupture of amniotic membranes and low birthweight babies may occur. Betamethasone and dexamethasone are used to treat the fetus. The effect on the fetus of bolus doses of methylprednisolone is unknown. Very little corticosteroid ingested by the mother enters her breast milk. Corticosteroid therapy in pregnancy is appropriate to control clinically active maternal illness; to treat an in utero infant suffering from neonatal lupus-associated carditis; in stress doses (in corticosteroid-treated patients) for labor and delivery: and, pre-delivery, to induce fetal lung maturation.