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.