Preliminary evidence of the effect of calcium supplementation on blood pressure in normal pregnant women.

In this study the hypothesis that calcium supplementation during pregnancy can modify blood pressure patterns in a population of normal pregnant women was tested. Thirty-six women with normal single pregnancies, between 20 and 35 years of age, in the second trimester of gestation (15 weeks), were randomly assigned to receive 1 gm of calcium per day (n = 11), 2 gm per day (n = 11), or a placebo (n = 14). No differences were observed at the times of admission into the study (baseline) in demographic and clinical variables or in the calcium intake of each group. Baseline blood pressure measures in several positions also were not different. After the initial blood pressure measures (fifteenth week), five follow-up blood pressure measures were obtained. The supplemented groups had significantly lower diastolic blood pressure than the control subjects between the twentieth and twenty-fourth weeks of gestation. Thereafter, an increase in the control group and the group receiving 1 gm of calcium was observed, but levels were similar at term. On the contrary, patients receiving 2 gm of calcium had blood pressure values that remained significantly lower throughout the third trimester. No differences or clear patterns were observed in the blood levels of calcium, magnesium, phosphorus, and proteins between and within groups during gestation. A possible explanation involving parathyroid hormone is attempted.