Calcium-phosphorus-magnesium homeostasis in women with threatened preterm delivery

Objective: The effect of threatened preterm delivery on calcium, phosphorus, magnesium homeostasis in the third trimester of pregnancy was investigated. Methods: Serum concentrations of total and ionized calcium, inorganic phosphorus, magnesium, total protein, albumin, total estrogens and human placental lactogen were determined in women with threatened preterm delivery at 29–36 weeks of gestation (the studied group) and in women with uncomplicated pregnancy of the same duration (the control group). Additionally, activities of total alkaline phosphatase and heat-stable alkaline phosphatase fraction were measured. Results: Patients of the studied group compared to the control group showed decreased concentration of total calcium (2.17 ± 0.09 vs. 2.28 ± 0.13 mmol/l, P < 0.0005), inorganic phosphorus (1.13 ± 0.27 vs. 1.32 ± 0.23 mmol/l, P < 0.001) and magnesium (0.64 ± 0.07 vs. 0.70 ± 0.10 mmol/l, P < 0.003); they also demonstrated decreased activity of total alkaline phosphatase (70.8 ± 23.2 vs. 81.9 ± 14.9 IU/l, P < 0.01) and its heat-stable fraction (30.2 ± 15.6 vs. 59.6 ± 14.9 IU/l, P < 0.001). In the studied group no difference was found in concentrations of investigated ions and enzymes between women who delivered at term and women who delivered prematurely. Patients with threatened preterm delivery showed serum deficiency of total calcium, phosphorus and magnesium which might be related to premature uterine contractility but does not predict premature labor by week 36 of gestation (66% of patients delivered at term). Conclusion: The deficiency of minerals and lowered activity of total alkaline phosphatase is observed in women with threatened preterm delivery. Laboratory tests of calcium-phosphorus-magnesium homeostatsis have limited predictive value in regard to the term of delivery in women with threatened preterm delivery.