Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems

Abstract

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 and the Cochrane Controlled Trials Register and we contacted study authors. Date of last search: February 2000.

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: Ten 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 0.35, 95% confidence interval 0.21 to 0.57) 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. 70, 95% confidence interval 0.58 to 0.83). The effect was greatest for women at high risk of hypertension (relative risk 0.22, 95% confidence interval 0.11 to 0.43) 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 0.43, 95% confidence interval 0.24 to 0. 79). 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 (RR0.59, 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.