Gestational hypertensive disorders are the second leading cause of maternal death worldwide. Epidemiological and clinical studies have shown that an inverse relationship exists between calcium intake and development of hypertension in pregnancy. The purpose of this review was to evaluate preventive effect of calcium supplementation during pregnancy on gestational hypertensive disorders and related maternal and neonatal morbidity and mortality. A literature search was carried out on PubMed, WHOLIS, PAHO and Cochrane Library. Only randomised trials were included in the review. Data were extracted into a standardised Excel sheet. Primary outcomes were pre-eclampsia, preterm birth and birthweight. Other neonatal outcomes such as neonatal mortality, small-for-gestational age and low birthweight were also evaluated. A total of 15 randomised controlled trials were included in this review. Pooled analysis showed that calcium supplementation during pregnancy reduced risk of pre-eclampsia by 52% [relative risk (RR) 0.48; 95% confidence interval (CI) 0.34, 0.67] and that of severe pre-eclampsia by 25% (RR 0.75 [95% CI 0.57, 0.98]). There was no effect on incidence of eclampsia (RR 0.73 [95% CI 0.41, 1.27]). There was a significant reduction for risk of maternal mortality/severe morbidity (RR 0.80 [95% CI 0.65, 0.97]). Calcium supplementation during pregnancy was also associated with a significant reduction in risk of pre-term birth (RR 0.76 [95% CI 0.60, 0.97]). There was an extra gain of 85 g in the intervention group compared with control (mean difference 85 g [95% CI 37, 133]). There was no effect of calcium supplementation on perinatal mortality (RR 0.90 [95% CI 0.74, 1.09]). There was a statistically non-significant increased risk of urolithiasis in the intervention group compared with control (RR 1.52 [95% CI 0.06, 40.67]). In conclusion, calcium supplementation during pregnancy is associated with a reduction in risk of gestational hypertensive disorders and pre-term birth and an increase in birthweight. There is no increased risk of kidney stones.