Effects of long-term antenatal magnesium sulfate administration on the bone mineralization of preterm infants

Aim: To evaluate the relationship between long-term antenatal magnesium sulfate (MgSO₄) administration and neonatal bone mineralization. Methods: Infants born at 28–33 weeks of gestation (n = 163) were divided into three groups: long-term Mg administration group (infants received antenatal MgSO₄ for ≥40 days), short-term Mg administration group (infants received antenatal MgSO₄ for <40 days), and non-Mg group. Serum calcium, phosphorus, Mg, and alkaline phosphatase were measured weekly up to 1 month of age, and the bone speed of sound (SOS) values were measured using quantitative ultrasound (QUS) at 1 week and 1 month after birth. Results: In the long-term Mg administration group, the serum calcium values were significantly lower, and the serum phosphorus, Mg, and alkaline phosphatase values were significantly higher than those in the non-Mg group at birth. Although these biochemical differences disappeared around the age of 2 weeks, the SOS values of the long-term Mg administration group were significantly lower than those of the non-Mg group both at 1 week and 1 month after birth (p = 0.02 and <0.001, respectively). When less than 10th percentile of SOS values at 1 month after birth in the non-Mg group was defined as poor bone mineralization, the cut-off value for the duration of antenatal MgSO₄ administration was 67 days. Conclusions: Long-term antenatal MgSO₄ administration affects bone mineralization during the early neonatal period, but the clinically acceptable duration of the administration based on its effects of bone mineralization assessed with QUS might be longer than a few weeks.