Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems

Background Pre-eclampsia and eclampsia are common causes of serious morbidity and death. Calcium supplementation may reduce the risk of preeclampsia through a number of mechanisms, and may help to prevent preterm birth. Objectives To assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child outcomes. Search strategy We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (May 2010) and contacted study authors. Selection criteria Randomised trials comparing at least 1 g daily of calcium during pregnancy with placebo. Data collection and analysis We assessed eligibility and trial quality, extracted and double-entered data. Main results We included 13 studies of good quality (involving 15,730 women). The average risk of high blood pressure was reduced with calcium supplementation rather than placebo (12 trials, 15,470 women: risk ratio (RR) 0.65, 95% confidence interval (CI) 0.53 to 0.81). There was also a reduction in the average risk of pre-eclampsia associated with calcium supplementation (13 trials, 15,730 women: RR 0.45, 95% CI 0.31 to 0.65). The effect was greatest for high-risk women (five trials, 587 women: RR 0.22, 95% CI 0.12 to 0.42), and those with low baseline calcium intake (eight trials, 10,678 women: RR 0.36, 95% CI 0.20 to 0.65). The average risk of preterm birth was reduced in the calcium group overall (11 trials, 15,275 women: RR 0.76, 95% CI 0.60 to 0.97) and amongst women at high risk of developing pre-eclampsia recruited to four small trials (568 women: RR 0.45, 95% CI 0.24 to 0.83). There was no overall effect on the risk of stillbirth or death before discharge from hospital (11 trials 15,665 babies; RR 0.90, 95% CI 0.74 to 1.09). The composite outcome maternal death or serious morbidity was reduced (four trials, 9732 women; RR 0.80, 95% CI 0.65 to 0.97). Most of 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). Blood pressure in childhood has been assessed in two studies, only one of which is currently included: 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 approximately halve the risk of pre-eclampsia, to reduce the risk of preterm birth and to reduce the rare occurrence of the composite outcome ' death or serious morbidity'. There were no other clear benefits, or harms.