A new Cochrane systematic review of 10 randomised trials involving over 37,000 pregnant women found that calcium supplementation results in little to no reduction in pre-eclampsia or related adverse maternal and perinatal outcomes.

Review: Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Image Credit: PanuShot / Shutterstock

High blood pressure in pregnancy is a major cause of death and severe disease in mothers and babies. The gravest complication is pre-eclampsia, associated with poor placental development and potentially affecting the mother’s liver, kidneys, and brain. Although calcium supplementation has long been considered a potential preventive strategy, especially for women with a prior history of pre-eclampsia, new evidence challenges its effectiveness for preventing hypertensive disorders of pregnancy.

Why Calcium Supplementation Was Considered a Preventive Strategy

Oral calcium is inexpensive, widely available, and generally safe for pregnant women and their babies. Earlier research suggested it might reduce blood pressure, including among women previously affected by pre-eclampsia. However, whether these blood-pressure effects translate into meaningful prevention of pre-eclampsia remains uncertain. This updated review incorporates stricter study-selection criteria and new data, resulting in a very different conclusion from earlier systematic reviews.

Review Objective: Testing Calcium’s Effects on Maternal and Neonatal Outcomes

The current Cochrane review aimed to determine whether calcium supplementation prevents pre-eclampsia and other hypertensive disorders of pregnancy. Researchers also evaluated whether calcium improves key outcomes, including maternal death, neonatal death, perinatal mortality, and preterm birth.

Stricter Study Selection and Study Characteristics

The review included only randomized controlled trials that met rigorous trustworthiness criteria, more stringent than in prior Cochrane reviews. Several earlier trials were excluded due to concerns about data integrity. Ten eligible studies (37,504 participants) were included. Eight trials compared calcium vs placebo, while two compared low-dose (500 mg/day) vs high-dose (1,500 mg/day) elemental calcium. Studies spanned low- to high-resource settings and included women with both low and adequate dietary calcium intake.

Placebo-Controlled Trials Show No Meaningful Reduction in Pre-Eclampsia

Across the eight placebo-controlled studies, calcium supplementation resulted in little difference in the incidence of pre-eclampsia. When restricting the analysis to large studies (≥500 participants), four trials involving 14,730 women provided high-certainty evidence that calcium supplementation is associated with little to no difference in pre-eclampsia risk compared with placebo.

No Evidence of Benefit for Maternal or Infant Health Outcomes

The authors found no convincing evidence that calcium supplementation reduces maternal death, severe complications of pre-eclampsia, or perinatal mortality. Calcium also did not significantly alter the risk of preterm birth, supported by high-certainty evidence in the large-study subgroup. Evidence on adverse effects remains uncertain due to limited reporting.

Dose Comparisons and Limitations in Subgroup Analyses

Low-dose vs high-dose calcium supplementation did not meaningfully change pre-eclampsia risk. Maternal death is too rare for meaningful dose-specific conclusions, and evidence regarding neonatal death remains very uncertain. Because most supplementation began mid-pregnancy, the review cannot assess whether very early calcium use might have different effects. Data were also insufficient to clearly differentiate effects among women with low vs adequate dietary calcium or high vs low pre-eclampsia risk, though subgroup analyses showed no important differences.

Final Conclusion: Calcium Unlikely to Prevent Pregnancy-Related Hypertension

The authors conclude that the newest, highest-quality evidence does not support calcium supplementation as an effective prevention strategy for pre-eclampsia or other hypertensive disorders of pregnancy. They note: “It is unlikely that further research would change the current evidence. Therefore, in future, research could focus on other ways to prevent blood pressure disorders during pregnancy.”

Journal reference:

Cluver, C. A., Rohwer, C., Rohwer, A. C. (2025). Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database of Systematic Reviews. doi: 10.1002/14651858.CD001059.pub6.