Calcium supplementation to prevent pre-eclampsia--a systematic review.

BACKGROUND

Calcium supplementation during pregnancy may prevent high blood pressure and preterm labour.

OBJECTIVE

To assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child adverse outcomes.

DESIGN

A systematic review of randomised trials that compared supplementation with at least 1 g calcium daily during pregnancy with placebo.

SEARCH STRATEGY

The Cochrane Pregnancy and Childbirth Group trials register (October 2001) and the Cochrane Controlled Trials Register (Issue 3, 2001) were searched and study authors were contacted.

DATA COLLECTION AND ANALYSIS

Eligibility and trial quality were assessed. Data were extracted and analysed.

MAIN RESULTS

There was a modest reduction in the risk of pre-eclampsia with calcium supplementation (relative risk (RR) 0.68, 95% confidence interval (CI): 0.57-0.81). The effect was greatest for women at high risk of hypertension (RR 0.21, 95% CI: 0.11-0.39) and those with low baseline calcium intake (RR 0.32, 95% CI: 0.21-0.49). There was no overall effect on the risk of preterm delivery, although there was a reduction in risk among women at high risk of hypertension (RR 0.42, 95% CI: 0.23-0.78). There was no evidence of any effect of calcium supplementation on stillbirth or death before discharge from hospital. There were fewer babies with birthweight < 2,500 g (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).

CONCLUSIONS

Calcium supplementation appears to be beneficial for women at high risk of gestational hypertension and in communities with low dietary calcium intake. These benefits were confined to several rather small trials, and were not found in the largest trial to date, conducted in a low-risk population. Further research is required.