Gestational Age‐Dependent Effects of Antenatal Magnesium Sulfate on Fetal S100B Levels: An Observational Study Using Cord Serum

ABSTRACT Aim Magnesium sulfate (MgSO 4 ) is widely used for fetal neuroprotection in preterm births before 32 weeks of gestation, yet it remains unclear whether its effect depends on gestational age. S100 calcium‐binding protein B (S100B), a protein secreted by astrocytes, is recognized as a biomarker of neural distress. This study aimed to investigate the relationship between antenatal MgSO 4 administration and umbilical cord serum S100B levels, with a focus on gestational age. Methods This retrospective study included women who delivered between 22 +0 and 33 +6 weeks of gestation at a tertiary center. Patients with hypertensive disorders of pregnancy, category 1 cesarean sections, multiple pregnancies, major congenital anomalies, or insufficient MgSO 4 administration were excluded. Cord blood samples were analyzed for S100B levels using ELISA. Multiple linear regression and restricted cubic spline modeling were performed to assess the association between MgSO 4 and S100B levels across different gestational ages. Results Among 69 eligible patients, MgSO 4 administration was significantly associated with higher cord serum S100B levels who delivered at ≥ 30 weeks of gestation (adjusted estimate 0.39, 95% confidence interval 0.17–0.62), but not in those who delivered at < 30 weeks (−0.12, −0.43 to 0.19) in multiple linear regression adjusted for birth weight and antenatal corticosteroids. This association remained consistent across multiple sensitivity analyses. S100B levels exhibited a gestational age‐dependent increase in response to MgSO 4 , peaking at approximately 32 weeks in restricted cubic spline modeling. Conclusions Antenatal MgSO 4 administration beyond 30 weeks of gestation at delivery is associated with increased fetal S100B levels, suggesting a potential gestational age‐specific response.