Approximately 30 g of calcium is accumulated during pregnancy, almost all of it in the fetal skeleton (25 g). For women with low calcium diets, there is low quality evidence to suggest that calcium supplementation during pregnancy may reduce the risk of preeclampsia. Low-quality evidence also suggests that calcium supplementation may reduce the risk of the mother having the baby before 37th week of pregnancy (preterm birth). The protective effect of calcium supplementation is not clear and there is not enough good quality to research to suggest best doses and timing of calcium supplementation.