Magnesium sulfate after 34 weeks shows no clear neonatal harm in retrospective cohort

Antenatal magnesium sulfate given to mothers after 34 weeks of gestation was not associated with worse short-term neonatal outcomes or higher rates of parent-reported developmental delay in a retrospective cohort study published in Archives of Gynecology and Obstetrics.

The study, led by Adi Shilony and colleagues, focused on late-preterm births, defined as deliveries between 34+0 and 36+6 weeks of gestation. The researchers set out to evaluate whether magnesium sulfate exposure after 34+0 weeks is linked to short- and long-term neonatal outcomes in this gestational window.

The retrospective cohort included children aged two years or older who were born at 34+0 to 36+6 weeks to mothers with preeclampsia between 2013 and 2020. The primary exposure was antenatal magnesium sulfate administration, and the analysis also examined different exposure durations of less than six hours, six to sixteen hours, and seventeen hours or more, as well as total doses above 30 grams.

Short-term outcomes assessed were respiratory distress, admission to the neonatal intensive care unit, a five-minute Apgar score of seven or below, and an umbilical cord pH of 7.1 or below. The primary long-term outcome was parent-reported, clinically diagnosed developmental delay affecting speech, cognition, or motor function, ascertained through a structured telephone questionnaire.

Of the 131 children born in the late preterm period, 59, or 45 percent, had been exposed to magnesium sulfate, while 72, or 55 percent, served as controls. Antenatal exposure was not associated with higher rates of respiratory distress, NICU admission, low five-minute Apgar scores, or low cord pH, and the findings were consistent across exposure durations and doses.

Rates of developmental delay were also similar between the exposed and unexposed groups, based on the parent-reported measure used in the study.

The authors concluded that 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, they cautioned that the limited sample size, sparse adverse events, residual confounding, and incomplete long-term follow-up preclude conclusions regarding equivalence or safety.

Because the study was retrospective and relied on parent-reported diagnoses for the long-term outcome, the findings should be interpreted as an absence of detected association rather than proof of safety. The researchers note that further work would be needed to establish whether magnesium sulfate exposure in the late preterm period has any effect on neonatal or developmental outcomes.

Subject of Research: Neonatal outcomes of antenatal magnesium sulfate exposure in late preterm births

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

Article References: Shilony, A., Shalev-Ram, H., Weiss, M., Cohen, G., Biron-Shental, T., & Shechter-Maor, G. (2026). Neonatal outcomes following magnesium sulfate exposure in the late preterm period (34 + 0–36 + 6 weeks). Archives of Gynecology and Obstetrics. https://doi.org/10.1007/s00404-026-08586-x

Image Credits: AI Generated

DOI: 10.1007/s00404-026-08586-x

Keywords: magnesium sulfate, late preterm, preeclampsia, neonatal outcomes, developmental delay, respiratory distress, NICU admission, retrospective cohort, Apgar score, gestational age, Neonatal, outcomes