Bold claim: Calcium supplements don’t shield pregnant people from pre-eclampsia, even after looking at thousands of participants across many trials. But here’s where it gets controversial: the latest, strongest evidence says the hoped-for benefits simply aren’t there. A comprehensive Cochrane review pooled data from 10 randomized trials involving more than 37,000 pregnant women and found calcium supplementation yields little to no reduction in pre-eclampsia or related maternal and perinatal outcomes.
What was studied and why it mattered
Pre-eclampsia is a leading cause of serious illness and death for mothers and babies, linked to poor placental development and potential damage to the liver, kidneys, and brain. Calcium has long been proposed as a cheap, accessible preventive strategy, especially for women with a history of hypertensive disorders in pregnancy. Yet new evidence challenges its effectiveness for preventing these conditions.
Why calcium was thought to help
Calcium pills are inexpensive, widely available, and generally safe for both mother and baby. Early studies hinted they could lower blood pressure, including in women who previously developed pre-eclampsia. The question remained, however: do these blood-pressure changes translate into real reductions in pre-eclampsia risk? This updated review applies stricter study criteria and incorporates new data, leading to conclusions that differ markedly from earlier reviews.
What the review set out to measure
The Cochrane review aimed to answer whether calcium supplementation prevents pre-eclampsia and other hypertensive disorders during pregnancy. It also looked at whether calcium improves key outcomes such as maternal death, neonatal death, perinatal mortality, and preterm birth.
How the analysis was done
Only randomized controlled trials that met rigorous trustworthiness standards were included, meaning some older trials were excluded due to data concerns. Ten eligible studies contributed data from 37,504 participants. Eight trials compared calcium to placebo, while two compared low-dose (500 mg/day) to high-dose (1,500 mg/day) elemental calcium. The included studies covered a range of settings and dietary calcium intakes.
Findings from placebo-controlled trials
In the eight placebo-controlled trials, calcium showed little difference in the rate of pre-eclampsia. Among the larger studies (each with at least 500 participants), four trials totaling 14,730 women provided high-certainty evidence that calcium supplementation does not meaningfully reduce pre-eclampsia risk compared with placebo.
Impact on maternal and neonatal outcomes
The review found no convincing evidence that calcium reduces maternal death, severe complications of pre-eclampsia, or perinatal mortality. It also did not significantly affect the risk of preterm birth, with high-certainty evidence supporting this null finding in the large-study subgroup. Reporting on adverse effects remained limited, leaving some uncertainty about potential harms.
Dose comparisons and subgroup limitations
Switching from low-dose to high-dose calcium did not meaningfully change pre-eclampsia risk. Because maternal death events are rare, dose-specific effects are hard to determine, and evidence on neonatal death remained very uncertain. Most trials started calcium later in pregnancy, so the analysis can’t address whether earlier, perhaps preconception or first-trimester, use might have different effects. Subgroup analyses by dietary calcium intake or baseline pre-eclampsia risk showed no clear differences.
Bottom line
The newest, highest-quality evidence indicates calcium supplementation during pregnancy does not effectively prevent pre-eclampsia or other hypertensive disorders, nor does it improve major maternal or perinatal outcomes. The authors suggest it is unlikely that further research would change this conclusion and propose that future work focus on alternative strategies to prevent blood-pressure disorders in pregnancy.
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.
