The effect of plurality and obesity on betamethasone concentrations in women at risk for preterm delivery.

Objective: Antenatal corticosteroids (ACS) decrease respiratory distress syndrome in singleton gestations. Twin data are less clear. Obesity and body mass index (BMI) also affect medication distribution volume. We evaluated whether maternal or neonatal cord betamethasone concentrations differed in twin gestations or obese patients.

Methods: Participants receiving betamethasone in a randomized controlled trial of weekly ACS were identified. We analyzed maternal delivery and cord serum betamethasone concentrations comparing singletons with twins and obese (BMI > or =30 kg/m(2)) with nonobese women.

Results: Fifty-five maternal and 45 cord blood samples were available. Unadjusted median maternal serum concentrations appeared paradoxically higher in both twin gestations and the obese. However, after controlling for confounders, there were no differences in betamethasone concentrations in maternal serum or cord blood between singletons and twins (P = .61 vs P = .14) or nonobese and obese women (P = .67 vs .12).

Conclusions: Maternal and umbilical cord blood serum betamethasone concentrations are not different in twin gestations or obese women.