Aims To determine whether antenatal magnesium sulfate (MgSO₄) administration correlates with circulating sulfate level in very/extremely preterm infants, and specifically whether non-exposed infants become sulphate deficient.

Methods Ion chromatography was used to measure plasma sulfate levels in preterm infants (<32 wk gestation) whose mothers did or did not receive antenatal MgSO₄.

Results Within 24 hours after birth, supra-physiological plasma sulfate levels were measured in infants whose mothers received MgSO₄ (mean±SD mmol/L 774±397, n=26), whereas sulfate levels in the group without MgSO₄ (257±162, n=10) were similar to that found in term cord blood. At 3 days and at 1 and 4 weeks of age, babies without antenatal MgSO₄ had reduced plasma sulfate level (3d: 190±96, n=49; 1 wk 118±61, n=67; 4 wk 125±79, n=6) whereas the group with antenatal MgSO₄ therapy maintained normal levels (3d: 287±160, n=68; 1 wk 250±125, n=119; 4 wk 228±89, n=56).

Conclusions These data positively correlate antenatal MgSO₄ administration with neonatal plasma sulfate levels, and suggest that unexposed preterm infants (who lack the capacity to generate sulphate) rapidly become sulphate depleted. Animal models and human studies demonstrate that sulphate is important for modulating brain development. It may be, therefore, that the neuroprotective benefit of antenatal MgSO₄ for preterm infants is attributable to the sulphate rather than the magnesium content. If sulfate neuroprotection is proven, then neonatal sulfate supplementation (in place of antenatal MgSO₄) may prove a simple and effective, low-cost, low-risk intervention universally available to all preterm infants to improve their chances of a normal neurodevelopmental outcome.