Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems.

BACKGROUND Calcium supplementation may prevent high blood pressure through a number of mechanisms and may help to prevent preterm labour. OBJECTIVES The objective of this review was to assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child adverse outcomes. SEARCH STRATEGY We searched the Cochrane Pregnancy and Childbirth Group trials register (October 2001) and the Cochrane Controlled Trials Register (Issue 3, 2001) and we contacted study authors. SELECTION CRITERIA Randomised trials comparing at least one gram daily of calcium during pregnancy with placebo. DATA COLLECTION AND ANALYSIS Eligibility and trial quality were assessed. Data extraction was carried out and double entered. MAIN RESULTS Eleven studies were included, all of good quality. There was a modest reduction in high blood pressure with calcium supplementation (relative risk 0.81, 95% confidence interval 0.74 to 0.89). The effect was greatest for women at high risk of hypertension (relative risk 0.45, 95% confidence interval 0.31 to 0.66) and those with low baseline dietary calcium (relative risk 0.49, 95% confidence interval 0.38 to 0.62). There was also a modest reduction in the risk of pre-eclampsia with calcium supplementation (relative risk 0.68, 95% confidence interval 0.57 to 0.81). The effect was greatest for women at high risk of hypertension (relative risk 0.21, 95% confidence interval 0.11 to 0.39) and those with low baseline calcium intake (relative risk 0.32, 95% confidence interval 0.21 to 0.49). There was no overall effect on the risk of preterm delivery, although there was a reduction in risk amongst women at high risk of hypertension (relative risk 0.42, 95% confidence interval 0.23 to 0.78). There was no evidence of any effect of calcium supplementation on stillbirth or death before discharge from hospital. There were fewer babies with birthweight < 2500g (RR 0.83, 95% CI 0.71-0.98). In one study, childhood systolic blood pressure > 95th percentile was reduced (RR 0.59, 95% CI 0.39-0.91). REVIEWER'S CONCLUSIONS Calcium supplementation appears to be beneficial for women at high risk of gestational hypertension and in communities with low dietary calcium intake. Optimum dosage requires further investigation.