Chorioamnionitis and earlier gestational age are associated with neonatal hypercalcemia after maternal magnesium sulfate therapy: A case-control study

Background: Magnesium sulfate (MgSO₄) is a tocolytic agent used to treat gestational hypertension and to prevent preterm labor. Neonatal hypocalcemia is a well-known side effect of maternal MgSO₄ use. Cases of neonatal hypercalcemia after maternal MgSO₄ have been reported. Little is known about neonatal hypercalcemia following maternal MgSO₄ therapy. We investigated the frequency and risk factors of neonatal hypercalcemia in this setting.

Methods: This case-control study investigated serum calcium in neonates born within 24 h after maternal MgSO₄ administration. We reviewed the electronic medical records of Saitama City Hospital for pregnant women who were treated with MgSO₄ between January 2016 and December 2021. There were 504 pregnant women that were treated with MgSO₄. We enrolled 257 neonates. Hypercalcemia was defined as serum albumin-corrected calcium greater than 2.74 mmol/L (11 mg/dL). We collected the perinatal information from the mothers and neonates.

Results: Twenty-one neonates (8%) had hypercalcemia at birth (H group). Umbilical arterial ionized calcium, neonatal plasma ionized calcium, and total serum calcium were significantly higher in H group than in N group. Neonatal serum albumin, on the other hand, was lower in H group than in N group. Neonates in H group were born earlier (28.4 ± 3.1 vs. 32.4 ± 3.1 wk, p < 0.001) and more likely to be born to mothers with pathological chorioamnionitis (91.0% vs. 12.7%, p < 0.001) than neonates who were normocalcemic (N group). Serum alkaline phosphatase was lower in H group (661 ± 276 vs. 816 ± 265 U/L, p = 0.01). Multivariate analysis showed that earlier gestational age and chorioamnionitis were significant risk factors.

Conclusion: Hypercalcemia after maternal MgSO₄ was seen in 8% of neonates. Maternal chorioamnionitis and earlier gestational age were associated with this condition.