Neonatal outcomes following magnesium sulfate exposure in the late preterm period (34 + 0–36 + 6 weeks)

Abstract Purpose To evaluate whether antenatal magnesium sulfate exposure after 34 + 0 weeks’ gestation is associated with short and long-term neonatal outcomes in the late preterm period. Late-preterm birth was defined as delivery between 34 + 0 and 36 + 6 weeks of gestation. Methods This retrospective cohort study included children aged ≥ 2 years born at 34 + 0–36 + 6 weeks’ gestation to mothers with preeclampsia between 2013 and 2020. The primary exposure was antenatal magnesium sulfate administration. Short-term outcomes included respiratory distress, neonatal intensive care unit (NICU) admission, 5-min Apgar score ≤ 7, and umbilical cord pH ≤ 7.1. The effects of different exposure durations (< 6 h, 6–16 h, ≥ 17 h) and total dose (> 30 g) were also evaluated. The primary long-term outcome was parent-reported clinically diagnosed developmental delay (speech, cognitive, or motor), ascertained through a structured telephone questionnaire. Results Among 131 children born in the late preterm period, 59 (45%) were exposed to magnesium sulfate and 72 (55%) served as controls. Antenatal magnesium sulfate exposure was not associated with higher rates of respiratory distress, NICU admission, 5-min Apgar score ≤ 7, or cord pH ≤ 7.1. Findings were consistent across exposure durations and doses. Rates of developmental delay were similar between groups. Conclusion Magnesium sulfate administration after 34 + 0 weeks for maternal indications was not associated with statistically clear differences in the short-term neonatal or developmental outcomes assessed. However, the limited sample size, sparse adverse events, residual confounding, and incomplete long-term follow-up preclude conclusions regarding equivalence or safety.