Calcium homeostasis in pregnancy during long‐term heparin treatment

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Abstract
Objective To investigate the effect of subcutaneous heparin treatment on calcium homeostasis in pregnancy. Design A longitudinal case-control observational study. Setting Department of Obstetrics and Gynaecology, Karolinska Hospital, Stockholm, Sweden. Subjects 36 pregnant women with previously verified thromboembolic complications and 23 healthy pregnant control women similar in age, parity, weight, and smoking habit. Interventions Thromboprophylaxis during pregnancy and 6 weeks post partum was given with subcutaneous heparin twice daily to the 36 women with a history of thromboembolic complications, 16 received an average dose of 24 500 IU/day and 20 a mean dose of 17 300 IU/day. Venous blood and urine samples were obtained every 4 weeks. Main outcome measures Serum concentrations of total calcium, ionized calcium, calcitonin and urinary calcium. Results Women on high-dose heparin treatment showed significantly higher concentrations of total and ionized calcium and of calcitonin in serum and significantly lower concentrations of calcium in urine than did 23 normal pregnant controls. The differences were most pronounced in the third trimester. The results obtained in the low-dose heparin group were between those in the high-dose and the control groups. At 8 weeks postpartum there were no significant differences between the heparin-treated women and the controls. No significant differences were found during pregnancy in haematocrit, liver or renal function, serum levels of albumin, phosphate, magnesium, alkaline phosphatase, parathyroid hormone or urinary cyclic AMP. Conclusions Heparin treatment during pregnancy results in changes in calcium homeostasis and a dose-dependent response is suggested.