Long-Term Tocolysis With Magnesium Sulfate as a Risk Factor for Low Bone Mass: A Case Series

Pregnancy and lactation-associated osteoporosis (PLO) is a disease caused by vertebral compression fracture, and it is characterized by low back pain during pregnancy or the postpartum period. However, it is difficult to predict and prevent PLO prepartum in high-risk groups. Recently, long-term tocolysis with magnesium sulfate (MgSO₄) has been reported to be associated with PLO. The purpose of this case series was to assess postpartum bone mass after long-term tocolysis with MgSO₄ and accumulated doses of MgSO₄. We report the case of a pregnant woman with vertebral compression fractures during pregnancy following long-term tocolysis with MgSO₄. We investigated whether long-term tocolysis with MgSO₄ was a high risk factor for PLO. Therefore, we retrospectively evaluated bone mineral density after delivery in nine women who had long-term tocolysis with MgSO₄ (more than 8 days) for treatment of threatened preterm birth at our hospital from January 2020 to December 2020. The age of the women was between 20 and 41 years (mean age, 30 years). The body mass index of the women was between 18.1 and 25.4 kg/m² (mean 20.0 kg/m²). Three women had a positive smoking history, and none had a family history of osteoporosis. The average duration of tocolysis with MgSO₄ was 11 - 97 days. The accumulated doses of MgSO₄ were between 168 and 3,756 g. Four of nine cases were diagnosed with low bone mass of young adult mean (YAM) value ≤ 80%. Of them, one case (accumulated doses of MgSO₄: 1,260 g) was diagnosed with PLO of YAM value ≤ 70%, and one case (accumulated doses of MgSO₄: 3,756 g) was diagnosed with bone fracture with a YAM value of ≤ 70%. Long-term tocolysis with MgSO₄ may be suggested as one of the risk factors of PLO. Nutritional guidance and rehabilitation are important interventions for target patients.