Should you take calcium during pregnancy?

If you already eat enough calcium, the best current evidence says a supplement probably does little for pre-eclampsia. The 2025 Cochrane review, restricted to trials it judged trustworthy, found a risk ratio of 0.83 (95% CI 0.67 to 1.04) across 6 trials in 15,364 pregnant women. In absolute terms that is about 9 fewer cases per 1000 women, somewhere between 17 fewer and 2 more, on low-certainty evidence. The open question is women whose diets are low in calcium, where WHO still recommends a supplement.

Unsettled. The answer changed in December 2025, and the change is still argued over. Older reviews found calcium roughly halved pre-eclampsia. The 2025 Cochrane update dropped 20 trials that earlier versions had counted, 9 of them over doubts about whether they were trustworthy, and the benefit shrank to a range that includes no effect. A 2026 commentary argues those exclusions were applied inconsistently. WHO advice predates the update.

What the trials found

Pre-eclampsia, in the trials that remain

When the 2025 Cochrane review kept only the 4 trials with at least 500 women each, 14,730 women in total, the risk ratio was 0.92 (95% CI 0.79 to 1.05). The reviewers rated that high-certainty evidence of little to no difference. The protective signal in older reviews came largely from small trials. The reviewers also report that baseline calcium intake did not change the result. The review was part-funded by WHO.

Two large placebo-controlled trials sit behind that picture. In the US CPEP trial, 4589 healthy first-time mothers took 2 g of calcium a day or a placebo, and 6.9% against 7.3% developed pre-eclampsia (RR 0.94, 95% CI 0.76 to 1.16). Those women mostly ate enough calcium already. In a WHO trial of 8325 first-time mothers whose diets held less than 600 mg a day, 1.5 g a day did not prevent pre-eclampsia either, 4.1% against 4.5%.

Severity and complications, in women with low intake

The same WHO trial found fewer serious outcomes on calcium. Eclampsia had a risk ratio of 0.68 (95% CI 0.48 to 0.97), a combined index of severe maternal illness and death 0.80 (0.70 to 0.91), and newborn deaths 0.70 (0.56 to 0.88). The authors state plainly that these were secondary outcomes, which means the trial was not designed to test them.

The older syntheses that disagree

A 2022 network meta-analysis of 30 trials in 20,445 women, which kept the trials Cochrane later excluded, found calcium about halved pre-eclampsia at a high dose (RR 0.49, 95% CI 0.36 to 0.66) and at a low dose (RR 0.49, 0.36 to 0.65). It did no trustworthiness screening. In the same analysis calcium was ineffective where women's average calcium intake was already adequate. That grouping is by the average in each trial, not by what each woman ate. A 2025 umbrella review of earlier meta-analyses reported a 47% reduction (RR 0.53, 0.42 to 0.68) with considerable heterogeneity, I2 84%. It was published before the Cochrane update and pools reviews that contain the excluded trials.

Dose

Two trials of 11,000 first-time mothers each, in India and Tanzania, compared 500 mg a day with 1500 mg. Pre-eclampsia was 3.0% against 3.6% in India (RR 0.84, 95% CI 0.68 to 1.03) and 3.0% against 2.7% in Tanzania (RR 1.10, 0.88 to 1.36), and the lower dose met the test for noninferiority in both. There was no placebo arm, so this shows the two doses perform alike, not that either works. Cochrane pooled the pair at a risk ratio of 0.96 (0.73 to 1.25), low-certainty evidence.

Preterm birth

A separate 2024 Cochrane review of 11 trials in 15,379 women found calcium probably slightly reduces birth before 37 weeks, RR 0.80 (95% CI 0.65 to 0.99), moderate-certainty evidence. It found no effect on birth before 34 weeks or on low birthweight. Its search ended in December 2022, and the 2025 review found little to no difference in preterm delivery in the large trials, RR 0.97, high certainty.

Starting before pregnancy, and the children later

One trial gave 500 mg a day from before conception to 1355 women who had pre-eclampsia in a previous pregnancy. The risk ratio was 0.84 (95% CI 0.62 to 1.14), low certainty, and only 633 of the women conceived during the trial. For the children, a 2022 review of 6 trials with 1616 children found too little evidence to say calcium in pregnancy affects health beyond the newborn period. One of those trials, 591 children, reported fewer with high systolic blood pressure at 5 to 7 years (RR 0.59, 0.39 to 0.90), in a review that flagged high attrition bias.

Who should be careful

The trials did not show clear harm. The 2024 Cochrane review of 19 trials found no sign that calcium raised gallstones, urinary stones, gut symptoms, headache, urinary infections or kidney problems. Adverse effects were sparsely reported, and the 2025 review rates that evidence very uncertain, RR 2.16 (95% CI 0.43 to 10.78) from 2 trials in 714 women. In the US CPEP trial, 2 g a day through pregnancy did not increase urinary stones, at a dose near the upper limit. The trials tested up to 2 g a day, and we could not quote an official upper limit for pregnancy, so nothing here supports taking more than that.

Not for everyone. Calcium supplements can interfere with some medicines, according to the NIH Office of Dietary Supplements. These include levothyroxine for an underactive thyroid, the HIV drug dolutegravir, lithium and quinolone antibiotics. Levothyroxine and dolutegravir are both used in pregnancy, and the timing of the doses matters. If you take any of them, ask whoever prescribes it how to space calcium around it.

What expert bodies say

WHO recommends 1.5 to 2.0 g of elemental calcium a day for pregnant women in populations with low dietary calcium, to reduce the risk of pre-eclampsia. That recommendation dates from 2018, was restated in 2020, and predates the Cochrane update that no longer supports a benefit. WHO recommends starting calcium before pregnancy only within rigorous research. It also says all women considering pregnancy should be counselled to get enough calcium from locally available calcium-rich foods.

The NIH Office of Dietary Supplements says calcium in pregnancy might reduce pre-eclampsia, but the benefit might apply only to women with inadequate intakes, and much of the evidence comes from studies with methodological weaknesses. Its fact sheet cites the 2018 Cochrane version. It also relays the American College of Obstetricians and Gynecologists, which says 1500 to 2000 mg a day might reduce the severity of pre-eclampsia in women eating less than 600 mg a day.

How we searched

What would change this answer

• An individual participant data meta-analysis of calcium in pregnancy, whose protocol was published in 2023 and whose results are not out yet. It can test the low-intake question with each woman's own diet rather than trial averages.
• A WHO review of its recommendation in light of the 2025 Cochrane update.
• A settled view on the trials Cochrane set aside. If they are judged trustworthy and return, the pooled benefit grows. If they stay out, the evidence for a benefit stays thin.
• A large placebo-controlled trial in women with low calcium intake that makes pre-eclampsia severity its main outcome. The WHO trial found its benefits only in secondary outcomes.
• Evidence on how to take calcium alongside iron in pregnancy. We found no trusted source on it.

Sources

1. ev-capg-01 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 15,364
   Calcium may result in little to no difference in pre-eclampsia (risk ratio (RR) 0.83, 95% confidence interval (CI) 0.67 to 1.04; 6 RCTs, 15,364 women; risk difference (RD) 9/1000 fewer, 95% CI 17 fewer to 2 more; low-certainty evidence).
   
   Who: pregnant women in placebo-controlled randomized trials of calcium supplementation, trials after 2010 prospectively registered
   Effect: pre-eclampsia RR 0.83 (95% CI 0.67 to 1.04); 6 RCTs; RD 9/1000 fewer (17 fewer to 2 more); low-certainty evidence
   Certainty: Best synthesis. Reverses earlier versions after trustworthiness screening; part-funded by WHO. Baseline calcium intake did not change the result per the authors.
   Cochrane Database Syst Rev, 2025 · checked 2026-10-06 · we read the abstract
2. ev-capg-02 · Meta-analysis or systematic review · Cochrane systematic review, sensitivity analysis excluding small trials · n = 14,730
   Sensitivity analysis excluding small studies (fewer than 500 participants) indicates little to no difference in pre-eclampsia (RR 0.92, 95% CI 0.79 to 1.05; 4 RCTs, 14,730 women; high-certainty evidence).
   
   Who: pregnant women in calcium vs placebo trials with at least 500 participants
   Effect: pre-eclampsia RR 0.92 (95% CI 0.79 to 1.05); 4 RCTs; high-certainty evidence
   Certainty: Small-study effect: the protective signal in older reviews came largely from small trials.
   Cochrane Database Syst Rev, 2025 · checked 2026-10-06 · we read the abstract
3. ev-capg-03 · Meta-analysis or systematic review · Cochrane systematic review, methods and included studies · n = 10 RCTs, 37,504 participants
   We excluded 20 previously included trials; 11 because eligibility criteria changed and nine because they are awaiting classification due to trustworthiness issues.
   
   Who: randomized trials of calcium supplementation in pregnancy
   Effect: 20 previously included trials excluded: 11 for changed eligibility criteria, 9 awaiting classification for trustworthiness
   Certainty: Source of the divergence with WHO and older meta-analyses; a 2026 commentary (PMID 42374462) argues the exclusions were applied inconsistently.
   Cochrane Database Syst Rev, 2025 · checked 2026-10-06 · we read the abstract
4. ev-capg-04 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 22,000
   There may be little to no difference between low- and high-dose calcium in pre-eclampsia (RR 0.96, 95% CI 0.73 to 1.25; 2 RCTs, 22,000 women; low-certainty evidence).
   
   Who: nulliparous pregnant women in low calcium-intake populations (India, Tanzania)
   Effect: low vs high dose pre-eclampsia RR 0.96 (95% CI 0.73 to 1.25); 2 RCTs; low-certainty evidence
   Certainty: Dose comparison only; no placebo arm in these two trials.
   Cochrane Database Syst Rev, 2025 · checked 2026-10-06 · we read the abstract
5. ev-capg-05 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 15,379
   Calcium supplementation probably slightly reduces the risk of preterm birth less than 37 weeks (average risk ratio (RR) 0.80, 95% confidence interval (CI) 0.65 to 0.99; 11 trials, 15,379 women; moderate-certainty evidence)
   
   Who: pregnant women in randomized trials of calcium vs placebo or no treatment, mostly high dose above 1000 mg a day
   Effect: preterm birth <37 weeks RR 0.80 (95% CI 0.65 to 0.99); 11 trials; moderate-certainty evidence; no effect on preterm birth <34 weeks or low birthweight
   Certainty: Searched to December 2022; the 2025 hypertension review found little to no difference in preterm delivery in large trials (RR 0.97, high certainty).
   Cochrane Database Syst Rev, 2024 · checked 2026-10-06 · we read the abstract
6. ev-capg-06 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 16,625
   There was no evidence that calcium supplementation had any effect on maternal weight gain during pregnancy; increasing bone mineral density in pregnant women; rate of intrauterine growth restriction; perinatal mortality; stillbirth or fetal death rate; increase birth length or fetal head circumference; and adverse effects such as postpartum haemorrhage, gall stones, gastrointestinal symptoms, headache, urinary stones, urinary tract infection or impaired renal function.
   
   Who: pregnant women in randomized trials of calcium vs placebo or no treatment
   Effect: no evidence of effect on postpartum hemorrhage, gall stones, gastrointestinal symptoms, headache, urinary stones, urinary tract infection or impaired renal function
   Certainty: Adverse effects were sparsely reported; the 2025 review rates adverse-effect evidence very uncertain (RR 2.16, 0.43 to 10.78; 2 RCTs, 714 women).
   Cochrane Database Syst Rev, 2024 · checked 2026-10-06 · we read the abstract
7. ev-capg-07 · Meta-analysis or systematic review · systematic review, meta-analysis and Bayesian network meta-analysis of randomized trials · n = 20,445
   Calcium supplementation prevented pre-eclampsia similarly with a high dose (RR 0.49, 95% CI 0.36-0.66) or a low dose (RR 0.49, 95% CI 0.36-0.65).
   
   Who: women before or during pregnancy in randomized trials of calcium supplementation
   Effect: high dose RR 0.49 (95% CI 0.36 to 0.66); low dose RR 0.49 (0.36 to 0.65); high vs low dose RR 0.79 (0.43 to 1.40)
   Certainty: No trustworthiness screening; includes small trials that drive the large effect. Shows why WHO and Cochrane now diverge.
   BJOG, 2022 · checked 2026-10-06 · we read the abstract
8. ev-capg-08 · Meta-analysis or systematic review · systematic review and network meta-analysis of randomized trials, subgroup analysis · n = 20,445
   Calcium was similarly effective regardless of baseline pre-eclampsia risk, vitamin D co-administration or timing of calcium initiation, but calcium was ineffective among women with adequate average baseline calcium intake.
   
   Who: women in randomized trials grouped by average baseline dietary calcium intake
   Effect: effective with low baseline intake; ineffective with adequate average baseline intake; similar by pre-eclampsia risk, vitamin D co-administration and timing
   Certainty: Subgroup by trial-level average intake, not individual intake.
   BJOG, 2022 · checked 2026-10-06 · we read the abstract
9. ev-capg-09 · Meta-analysis or systematic review · umbrella review of systematic reviews and meta-analyses · n = —
   Results: Calcium supplementation reduced the risk of preeclampsia by 47% (RR: 0.53, 95% CI: 0.42, 0.68) with a considerable level of heterogeneity (I2 = 84.39%).
   
   Who: pregnant women in systematic reviews and meta-analyses of calcium supplementation, searched to December 2023
   Effect: RR 0.53 (95% CI 0.42 to 0.68), I2 84%; high-risk RR 0.35 (0.26 to 0.47); low-risk RR 0.67 (0.59 to 0.77)
   Certainty: Pools older reviews that contain trials later excluded by Cochrane 2025; predates that update.
   Front Med (Lausanne), 2025 · checked 2026-10-06 · we read the abstract
10. ev-capg-10 · Randomized controlled trial(s) · two independent randomized noninferiority trials, 500 mg vs 1500 mg daily calcium carbonate · n = 22,000
    The cumulative incidence of preeclampsia was 3.0% in the 500-mg group and 3.6% in the 1500-mg group in the India trial (relative risk, 0.84; 95% confidence interval [CI], 0.68 to 1.03) and 3.0% and 2.7%, respectively, in the Tanzania trial (relative risk, 1.10; 95% CI, 0.88 to 1.36) - findings consistent with the noninferiority of the lower dose in both trials.
    
    Who: nulliparous pregnant women in India and Tanzania
    Effect: pre-eclampsia 3.0% vs 3.6% (RR 0.84, 95% CI 0.68 to 1.03) in India; 3.0% vs 2.7% (RR 1.10, 0.88 to 1.36) in Tanzania; preterm noninferiority met in India, not in Tanzania
    Certainty: No placebo arm, so it shows dose equivalence, not that calcium works. NCT03350516, completed 2022.
    N Engl J Med, 2024 · checked 2026-10-06 · we read the abstract
11. ev-capg-11 · Randomized controlled trial(s) · randomized placebo-controlled double-blind multicentre trial, 1.5 g calcium a day from before 20 weeks · n = 8325
    A 1.5-g calcium/day supplement did not prevent preeclampsia but did reduce its severity, maternal morbidity, and neonatal mortality, albeit these were secondary outcomes.
    
    Who: nulliparous normotensive women from populations with dietary calcium below 600 mg a day
    Effect: pre-eclampsia 4.1% vs 4.5% (not significant); eclampsia RR 0.68 (95% CI 0.48 to 0.97); severe maternal morbidity and mortality index RR 0.80 (0.70 to 0.91); neonatal mortality RR 0.70 (0.56 to 0.88)
    Certainty: Benefits were secondary outcomes, as the authors state.
    Am J Obstet Gynecol, 2006 · checked 2026-10-06 · we read the abstract
12. ev-capg-12 · Randomized controlled trial(s) · randomized placebo-controlled multicentre trial, 2 g elemental calcium daily · n = 4589
    Calcium supplementation did not significantly reduce the incidence or severity of preeclampsia or delay its onset.
    
    Who: healthy nulliparous women 13 to 21 weeks pregnant, United States
    Effect: pre-eclampsia 6.9% vs 7.3% (RR 0.94, 95% CI 0.76 to 1.16); no difference in hypertension or perinatal outcomes
    Certainty: US women mostly had adequate calcium intake, so the result speaks to well-fed populations.
    N Engl J Med, 1997 · checked 2026-10-06 · we read the abstract
13. ev-capg-13 · Randomized controlled trial(s) · randomized placebo-controlled multicentre trial · n = 4589
    Calcium did not reduce the numbers of preterm deliveries, small-for-gestational-age births, or fetal and neonatal deaths; nor did it increase urolithiasis during pregnancy.
    
    Who: healthy nulliparous women 13 to 21 weeks pregnant, United States
    Effect: no increase in urolithiasis with 2 g/day elemental calcium vs placebo
    Certainty: Stones were a secondary safety outcome; dose near the upper limit.
    N Engl J Med, 1997 · checked 2026-10-06 · we read the abstract
14. ev-capg-14 · Meta-analysis or systematic review · Cochrane systematic review of randomized trials (one trial) · n = 1355
    Compared to placebo, calcium may result in little to no difference in pre-eclampsia (RR 0.84, 95% CI 0.62 to 1.14; 1 RCT, 1355 women; RD 19/1000 fewer, 95% CI 46 fewer to 17 more; low-certainty evidence).
    
    Who: parous women whose most recent pregnancy had pre-eclampsia or eclampsia, 500 mg a day from before conception
    Effect: pre-eclampsia RR 0.84 (95% CI 0.62 to 1.14); RD 19/1000 fewer (46 fewer to 17 more); low-certainty evidence
    Certainty: Single trial; only 633 women conceived during the trial.
    Cochrane Database Syst Rev, 2025 · checked 2026-10-06 · we read the abstract
15. ev-capg-15 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 1616
    Limited available data from RCTs do not provide sufficient evidence to conclude that prenatal calcium supplementation influences offspring health outcomes beyond the newborn period.
    
    Who: offspring of women in randomized trials of calcium with or without vitamin D in pregnancy
    Effect: one trial (591 children): high systolic blood pressure at 5-7 years RR 0.59 (95% CI 0.39 to 0.90); growth, metabolic and neurodevelopmental effects unknown
    Certainty: High attrition bias; conflicting or insufficient data.
    Ann N Y Acad Sci, 2022 · checked 2026-10-06 · we read the abstract
16. ev-capg-16 · Position of an expert body · WHO guideline recommendation · n = —
    The GDG noted that in 2018 WHO revalidated the recommendation that in populations with low dietary calcium intake, daily calcium supplementation (1.5–2.0 g oral elemental calcium) is recommended for pregnant women to reduce the risk of pre-eclampsia (1).
    
    Who: pregnant women in populations with low dietary calcium intake
    Effect: 1.5-2.0 g oral elemental calcium daily (2018 recommendation, restated 2020)
    Certainty: Predates Cochrane 2025, which no longer supports a benefit; WHO had not changed the dose as of the web pass (2026-10-06).
    World Health Organization, WHO recommendation on calcium supplementation before pregnancy for the prevention of pre-eclampsia and its complications, 2020 · checked 2026-10-06 · we read the section
17. ev-capg-17 · Position of an expert body · WHO guideline recommendation · n = —
    Pre-pregnancy calcium supplementation for the prevention of pre-eclampsia and its complications is recommended only in the context of rigorous research.
    
    Who: women intending to become pregnant
    Effect: recommendation in research context only
    Certainty: Based on low-certainty evidence from one trial (see ev-capg-14).
    World Health Organization, WHO recommendation on calcium supplementation before pregnancy for the prevention of pre-eclampsia and its complications, 2020 · checked 2026-10-06 · we read the section
18. ev-capg-18 · Position of an expert body · WHO guideline recommendation · n = —
    Dietary counselling of all women who are considering pregnancy should promote adequate calcium intake through locally available, calcium-rich foods.
    
    Who: all women considering pregnancy
    Effect: dietary counseling on calcium-rich foods; staple-food fortification where intake is low
    Certainty: Food-first advice applies regardless of the supplement debate.
    World Health Organization, WHO recommendation on calcium supplementation before pregnancy for the prevention of pre-eclampsia and its complications, 2020 · checked 2026-10-06 · we read the section
19. ev-capg-19 · Position of an expert body · government fact sheet · n = —
    Calcium supplementation during pregnancy might reduce the risk of preeclampsia, but the benefits might apply only to women with inadequate calcium intakes, and much of this evidence comes from studies with methodological weaknesses [77,78].
    
    Who: pregnant women
    Effect: possible benefit limited to inadequate calcium intakes
    Certainty: Fact sheet cites the 2018 Cochrane version, not the 2025 update.
    NIH Office of Dietary Supplements, Calcium fact sheet for health professionals · checked 2026-10-06 · we read the section
20. ev-capg-20 · Position of an expert body · government fact sheet · n = —
    For example, the American College of Obstetrics and Gynecology states that daily supplementation with 1,500 to 2,000 mg calcium might reduce the severity of preeclampsia in pregnant women who have calcium intakes of less than 600 mg/day [77].
    
    Who: pregnant women with calcium intakes below 600 mg a day
    Effect: 1500-2000 mg/day calcium might reduce severity of preeclampsia
    Certainty: ACOG position relayed by ODS; ACOG itself not in trust.json.
    NIH Office of Dietary Supplements, Calcium fact sheet for health professionals · checked 2026-10-06 · we read the section
21. ev-capg-21 · Position of an expert body · government fact sheet · n = —
    These medications include dolutegravir, levothyroxine, lithium, and quinolone antibiotics.
    
    Who: people taking these medications, including pregnant women
    Effect: interaction with dolutegravir, levothyroxine, lithium and quinolone antibiotics
    Certainty: Levothyroxine and dolutegravir are both used in pregnancy; dose timing matters.
    NIH Office of Dietary Supplements, Calcium fact sheet for health professionals · checked 2026-10-06 · we read the section