Calcium supplementation is associated with a significant protective benefit in the prevention of pre-eclampsia, and should be used for this indication according to a previous review. This review indicates that there are no additional benefits for calcium supplementation in prevention of preterm birth or low infant birth weight. While there was a statistically significant difference of 80 g identified in mean infant birth weight, there was significant heterogeneity identified, and the clinical significance of this difference is uncertain.
Calcium supplementation in mild preeclampsia remote from term: a randomized double-blind clinical trial.
To determine whether calcium supplementation prevents progression to severe disease in preterm nulliparous women with mild preeclampsia.
                Seventy-five women hospitalized at 24-36 weeks' gestation because of mild preeclampsia were randomized to receive either 2 g/day of elemental calcium (36 women) or placebo (39). Both groups had similar demographic characteristics, initial blood pressure measurements, and amount of proteinuria. Diagnostic criteria and clinical management for severe preeclampsia were applied consistently.
                Eighteen of 36 calcium-treated subjects (50%, 95% confidence interval [CI] 33-67) developed severe preeclampsia, compared with 19 of 39 (48.7%, 95% CI 32-65) in the placebo group (relative risk 1.03, 95% CI 0.64-1.03; P = 1.00). Blood pressure values, gestational age at delivery, newborn weights, incidence of low Apgar scores, and umbilical arterial blood gases were similar for the two groups.
                Calcium supplementation does not prevent severe preeclampsia in preterm patients with mild disease.