ObjectiveTo determine the effect of third-trimester calcium supplementation on maternal hemodynamic function.MethodsPregnant women were randomized to receive either 1.5 g of elemental calcium or placebo for 6 weeks during the third trimester. Using Doppler technique, maternal hemodynamic characteristics were measured at baseline, at 2 hours after the first dose of study drug, and at the completion of 6 weeks. Serum, dietary, and urinary calcium levels were also assessed. Power calculation indicated the need to study ten subjects in each group to detect a 1.2 L (20%) difference in cardiac output between groups, assuming a mean of 6.2 ± 1.0 L/minute. Data were analyzed by analysis of variance for repeated measures, Student t test, Mann-Whitney U test, and Fisher exact test.ResultsTwenty-three women enrolled, and 18 completed 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 significant differences in hemodynamic function over time within the calcium supplementation or placebo group (P> .05; analysis of variance for repeated measures). After 6 weeks, there were no significant differences 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.ConclusionsThese findings suggest that third-trimester calcium supplementation does not significantly alter cardiac output. The mechanism by which calcium supplementation lowers blood pressure remains to be elucidated.