Association between the prolonged use of magnesium sulfate for tocolysis and fracture risk among infants

In 2013, the U.S. Food and Drug Administration issued a safety warning that cautioned against using magnesium sulfate (MgSO₄) injections for more than 5 to 7 days to stop preterm delivery due to the bone problems subsequently observed in infants. However, the warning was mainly based on case reports, and further investigation is necessary to determine whether prolonged MgSO₄ use increased infant fractures. To evaluate whether prolonged MgSO₄ use for tocolysis increased the risk of subsequent fractures among infants. A retrospective population-based cohort study was conducted with a new-user study design using the National Health Insurance Database in Taiwan. We included pregnant women aged between 12 and 55 years old who delivered a live-born singleton. The enrollment period was from January 1, 2012 to December 31, 2014. The exposure group was defined as pregnant women who received MgSO₄ injection for >5 days during pregnancy, while those not receiving any tocolytics were the reference group. The outcome was any bone fracture among the infants during the 2-year follow-up period. Propensity score matching and Cox proportional hazards regression models were used to estimate the hazard of fractures. We further studied the effect of MgSO₄ treatment with varied dosages and durations of treatment in the sensitivity analyses. Among the 4092 pregnant women in the database, 693 (16.9%) of them were included in the exposure group. The hazard ratio of infant fractures among prolonged MgSO₄ users was not significantly different from that of tocolytic nonusers in adjusted models (adjusted hazard ratio (aHR) = 1.48; 95% confidence interval (CI) = 0.59–3.71). A similar lack of significance was found in the sensitivity analyses (aHR = 1.45; 95% CI = 0.40–5.28 for larger treatment dosage; aHR = 2.52; 95% CI = 0.49–12.98 for longer treatment duration). Prolonged MgSO₄ tocolysis use did not increase the risk of infant fractures. Our findings reconfirmed the safety of MgSO₄ as a tocolytic treatment.