Parathyroid hormone and calcitriol changes in normal and insulin-dependent diabetic pregnancies

In pregnancy, an increase in serum calcitriol and parathyroid hormone concentrations has been reported in several studies, though the increase in parathyroid hormone remains controversial. In magnesium deficiency states, parathyroid hormone and calcitriol secretion may be decreased. Because magnesium deficiency may occur in insulin-dependent diabetic patients, mainly because of urinary magnesium losses, we hypothesized that serum parathyroid hormone and calcitriol do not increase in the diabetic pregnancy. We studied, in a prospective longitudinal manner, 35 nondiabetic and 199 insulin-dependent diabetic pregnancies. In diabetic women, the goals of glycemic control were fasting blood glucose below 100 mg/dL and postprandial blood glucose less than 140 mg/dL. Serum magnesium, calcium, parathyroid hormone (whole molecule; ie, 1-84 fragment), and calcitriol were measured three times: 1) 8-12 weeks, 2) 22-28 weeks, and 3) 32-38 weeks' gestation. In normal women, serum parathyroid hormone did not change significantly over pregnancy, and a wide scatter of values was observed. Serum calcitriol increased significantly with advancing gestation. In diabetic women, serum parathyroid hormone had a narrow scatter, but values were within the low-normal range. During the third trimester there was no increase, and even a decrease, in serum calcitriol concentrations. Diabetics had, throughout pregnancy, significantly reduced serum magnesium concentrations when compared with controls. Their serum calcium and ionized calcium concentrations were similar to those of controls, except in the third trimester, when diabetic women had significantly lower serum calcium and ionized calcium concentrations than controls. We speculate that mineral metabolism abnormalities in diabetic pregnancies might be due to relative magnesium and/or insulin deficiency.