Evidence from randomised controlled trials shows that calcium supplements help prevent pre-eclampsia and preterm birth and lower the risk of a woman dying or having serious problems related to high blood pressure in pregnancy. This is particularly for women on low calcium diets.
Pre-eclampsia is evident as high blood pressure and protein in the urine. It 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 24 trials found good quality evidence that calcium supplementation with high doses (at least 1 g daily) during pregnancy (13 studies involving 15,730 women) is a safe and relatively cheap way of reducing the risk of pre-eclampsia, especially in women from communities with low dietary calcium and those at increased risk of pre-eclampsia. Women receiving calcium supplements were also less likely to die or have serious problems related to pre-eclampsia. Babies were less likely to be born preterm. No adverse effects have been found but further research is needed into the ideal dosage of supplementation. Limited evidence from 10 trials (2234 women) suggested that a relatively low dose may be effective although co-interventions such as vitamin D, linoleic acid or antioxidants were given in six of the included trials.
In settings of low dietary calcium where high-dose supplementation is not feasible, the option of lower dose supplements (500 to 600 mg/day) might be considered in preference to no supplementation.