LAUSR

Objective Antenatal magnesium sulfate (MgSO4) is known to affect the central nervous system of preterm infants, and there is biologic rationale for influence on other phenotypes. This study investigated the effect of MgSO4exposure on the trajectory of ponderal index (PI, kg/m3) from birth to 2 years of age. Study Design A secondary analysis of a U.S. randomized controlled trial investigating MgSO4versus placebo administration among women at high risk for preterm delivery was performed. Multivariable logistic regression was used to assess the relationship between PI from birth to 2 years of age and exposure to MgSO4versus placebo. Results There was a larger decrement in PI from birth to 2 years of age in infants exposed to MgSO4compared with placebo (p = 0.032). There was a statistically significant one‐way interaction between newborn sex and treatment group (p = 0.019). Change in PI in males exhibited a greater decrement in those exposed to MgSO4versus placebo (p = 0.227), whereas female infants exposed to MgSO4had a smaller decrement (p = 0.04). Conclusion MgSO4exposure in preterm infants is associated with a larger decrease in PI from birth to 2 years of age. In addition, the direction of effect of MgSO4on the change in PI over the first 2 years of life is different by sex.