Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems
Abstract
Background
Pre‐eclampsia and eclampsia are common causes of serious morbidity and death. Calcium supplementation may reduce the risk of pre‐eclampsia through a number of mechanisms, and may help to prevent preterm labour.
Objectives
To assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child outcomes.
Search methods
We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (February 2006), the Cochrane Central Register of Controlled Trials (The Cochrane Library, 2005, Issue 4), and contacted study authors. We updated the search of the Cochrane Pregnancy and Childbirth Group's Trials Register on 31st October 2009 and added the results to the awaiting classification section of the review.
Selection criteria
Randomised trials comparing at least one gram daily of calcium during pregnancy with placebo.
Data collection and analysis
We assessed eligibility and trial quality, extracted and double‐entered data.
Main results
Twelve studies of good quality were included. The risk of high blood pressure was reduced with calcium supplementation rather than placebo (11 trials, 14,946 women: relative risk (RR) 0.70, 95% confidence interval (CI) 0.57 to 0.86). There was also a reduction in the risk of pre‐eclampsia associated with calcium supplementation (12 trials, 15,206 women: RR 0.48, 95% CI 0.33 to 0.69). The effect was greatest for high‐risk women (5 trials, 587 women: RR 0.22, 95% CI 0.12 to 0.42), and those with low baseline calcium intake (7 trials, 10,154 women: RR 0.36, 95% CI 0.18 to 0.70).
The composite outcome maternal death or serious morbidity was reduced (4 trials, 9732 women; RR 0.80, 0.65 to 0.97). Almost all the women in these trials were low risk and had a low calcium diet. Maternal deaths were reported in only one trial. One death occurred in the calcium group and six in the placebo group, a difference which was not statistically significant (RR 0.17, 95% CI 0.02 to 1.39).
There was no overall effect on the risk of preterm birth (10 trials, 14,751 women: RR 0.81, 95% CI 0.64 to 1.03), or stillbirth or death before discharge from hospital (10 trials 15,141 babies; RR 0.89, 95% CI 0.73 to 1.09).
Blood pressure in childhood has been assessed in one study: childhood systolic blood pressure greater than 95th percentile was reduced (514 children: RR 0.59, 95% CI 0.39 to 0.91).
Authors' conclusions
Calcium supplementation appears to almost halve the risk of pre‐eclampsia, and to reduce the rare occurrence of the composite outcome 'death or serious morbidity'. There were no other clear benefits, or harms.
[Note: The 15 citations in the awaiting classification section of the review may alter the conclusions of the review once assessed.]
PICOs
Plain language summary
Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems
Calcium supplements help prevent pre‐eclampsia, lowers the risk of the woman dying or having serious problems.
Pre‐eclampsia is a major cause of death in pregnant women and newborn babies worldwide. Preterm birth (birth before 37 weeks) is often caused by high blood pressure and is the leading cause of newborn deaths, particularly in low‐income countries. The review of trials found that calcium supplementation during pregnancy is a safe and relatively cheap means of reducing the risk of pre‐eclampsia in women at increased risk, and women from communities with low dietary calcium. Women were also less likely to die or have serious problems due to pre‐eclampsia. No adverse effects have been found but further research is needed into the ideal dosage for supplementation.
