A RANDOMIZED CONTROLLED TRIAL OF THE EFFECT OF 3RD-TRIMESTER CALCIUM SUPPLEMENTATION ON MATERNAL HEMODYNAMIC FUNCTION

Objective: To determine the effect of third-trimester calcium suppleme ntation on maternal hemodynamic function. Methods: pregnant women were randomized to receive either 1.5 g of elemental calcium or placebo fo r 6 weeks during the third trimester. Using Doppler technique, materna l hemodynamic characteristics were measured at baseline, at 2 hours af ter the first dose of study drug, and at the completion of 6 weeks. Se rum, dietary, and urinary calcium levels were also assessed. Power cal culation indicated the need to study ten subjects in each group to det ect a 1.2 L (20%) difference in cardiac output between groups, assumin g a mean of 6.2 +/- 1.0 L/minute. Data were analyzed by analysis of va riance for repeated measures, Student t test, Mann-Whitney U test, and Fisher exact test. Results: Twenty-three women enrolled, and 18 compl eted the study. There were no statistically significant differences in demographic characteristics or in serum, dietary, or urinary calcium levels between the two groups. There were also no statistically signif icant differences in hemodynamic function over time within the calcium supplementation or placebo group (P > .05; analysis of variance for r epeated measures). After 6 weeks, there were no significant difference s between the calcium- and placebo-treated subjects in any hemodynamic measurement. Specifically, there was not a statistically significant difference in cardiac output (7.3 +/- 1.2 L/minute versus 8.0 +/- 0.9 L/minute; P = .09) between the calcium- and placebo-treated groups. Co nclusion: These findings suggest that third-trimester calcium suppleme ntation does not significantly alter cardiac output. The mechanism by which calcium supplementation lowers blood pressure remains to be eluc idated. ((C) 1997 by The American College of Obstetricians and Gynecol ogists.)