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Cochrane Database of Systematic Reviews

Calcium supplementation commencing before or early in pregnancy, or food fortification with calcium, for preventing hypertensive disorders of pregnancy

Overview of attention for article published in Cochrane database of systematic reviews, September 2017
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  • In the top 25% of all research outputs scored by Altmetric
  • High Attention Score compared to outputs of the same age (91st percentile)
  • Good Attention Score compared to outputs of the same age and source (74th percentile)

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Calcium supplementation commencing before or early in pregnancy, or food fortification with calcium, for preventing hypertensive disorders of pregnancy
Published in
Cochrane database of systematic reviews, September 2017
DOI 10.1002/14651858.cd011192.pub2
Pubmed ID

G Justus Hofmeyr, Sarah Manyame


Pre-eclampsia is considerably more prevalent in low- than high-income countries. One possible explanation for this discrepancy is dietary differences, particularly calcium deficiency. Calcium supplementation in the second half of pregnancy reduces the serious consequences of pre-eclampsia and is recommended by the World Health Organization (WHO) for women with low dietary calcium intake, but has limited effect on the overall risk of pre-eclampsia. It is important to establish whether calcium supplementation before and in early pregnancy has added benefit. Such evidence would be justification for population-level fortification of staple foods with calcium. To determine the effect of calcium supplementation or food fortification with calcium, commenced before or early in pregnancy and continued at least until mid-pregnancy, on pre-eclampsia and other hypertensive disorders, maternal morbidity and mortality, as well as fetal and neonatal outcomes. We searched the Cochrane Pregnancy and Childbirth Trials Register (10 August 2017), PubMed (29 June 2017), ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP) (10 August 2017) and reference lists of retrieved studies. Randomised controlled trials of calcium supplementation or food fortification which include women of child bearing age not yet pregnant, or in early pregnancy. Cluster-RCTs, quasi-RCTs and trials published in abstract form only would have been eligible for inclusion in this review but none were identified. Cross-over designs are not appropriate for this intervention.The scope of this review is to consider interventions including calcium supplementation with or without additional supplements or treatments, compared with placebo or no intervention. Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. This review is based on one RCT (involving 60 women) which looked at calcium plus additional supplements versus control. The women (who had low antioxidant status) were in the early stages of pregnancy. We did not identify any studies where supplementation commenced pre-pregnancy. Another RCT comparing calcium versus placebo is ongoing but not yet complete. We did not identify any studies looking at any of our other planned comparisons. Calcium plus antioxidants and other supplements versus placeboWe included one small study (involving 60 women with low antioxidant levels) which was conducted in an academic hospital in Indondesia. The study was at low risk of bias for all domains with the exception of selective reporting, for which it was unclear. Women in the intervention group received calcium (800 mg) plus N-acetylcysteine (200 mg), Cu (2 mg), Zn (15 mg), Mn (0.5 mg) and selenium (100 mcg) and vitamins A (1000 IU), B6 (2.2 mg), B12 (2.2 mcg), C (200 mg), and E (400 IU) versus the placebo control group of women who received similar looking tablets containing iron and folic acid. Both groups received iron (30 mg) and folic acid (400 mcg). Tablets were taken twice daily from eight to 12 weeks of gestation and then throughout pregnancy.The included study found that calcium supplementation plus antioxidants and other supplements may slightly reduce pre-eclampsia (gestational hypertension and proteinuria) (risk ratio (RR) 0.24, 95% confidence interval (CI) 0.06 to 1.01; low-quality evidence), but this is uncertain due to wide confidence intervals just crossing the line of no effect, and small sample size. It appears that earlypregnancy loss before 20 weeks' gestation (RR 0.06, 95% CI 0.00 to 1.04; moderate-quality evidence) may be slightly reduced by calcium plus antioxidants and other supplements, but this outcome also has wide confidence intervals, which just cross the line of no effect. Very few events were reported under the composite outcome, severe maternal morbidity and mortality index and no clear difference was seen between groups (RR 0.36, 95% CI 0.04 to 3.23; low-quality evidence). However, the included study observed a reduction in the composite outcome pre-eclampsia and/or pregnancy loss at any gestational age (RR 0.13, 95% CI 0.03 to 0.50; moderate-quality evidence), and pregnancy loss/stillbirth at any gestational age (RR 0.06, 95% CI 0.00 to 0.92; moderate-quality evidence) in the calcium plus antioxidant/supplement group.Other outcomes reported (placental abruption, severe pre-eclampsia and preterm birth (less than 37 weeks' gestation)) were too infrequent for meaningful analysis. No data were reported for the outcomes caesarean section, birthweight < 2500 g, Apgar score less than seven at five minutes, death or admission to neonatal intensive care unit (ICU), or pregnancy loss, stillbirth or neonatal death before discharge from hospital. The results of this review are based on one small study in which the calcium intervention group also received antioxidants and other supplements. Therefore, we are uncertain whether any of the effects observed in the study were due to calcium supplementation or not. The evidence in this review was graded low to moderate due to imprecision. There is insufficient evidence on the effectiveness or otherwise of pre- or early-pregnancy calcium supplementation, or food fortification for preventing hypertensive disorders of pregnancy.Further research is needed to determine whether pre- or early-pregnancy supplementation, or food fortification with calcium is associated with a reduction in adverse pregnancy outcomes such as pre-eclampsia and pregnancy loss. Such studies should be adequately powered, limited to calcium supplementation, placebo-controlled, and include relevant outcomes such as those chosen for this review.There is one ongoing study of calcium supplementation alone versus placebo and this may provide additional evidence in future updates.

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X Demographics

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Mendeley readers

Mendeley readers

The data shown below were compiled from readership statistics for 274 Mendeley readers of this research output. Click here to see the associated Mendeley record.

Geographical breakdown

Country Count As %
Unknown 274 100%

Demographic breakdown

Readers by professional status Count As %
Student > Master 48 18%
Student > Bachelor 31 11%
Researcher 29 11%
Student > Ph. D. Student 24 9%
Student > Postgraduate 12 4%
Other 34 12%
Unknown 96 35%
Readers by discipline Count As %
Medicine and Dentistry 74 27%
Nursing and Health Professions 42 15%
Agricultural and Biological Sciences 14 5%
Social Sciences 9 3%
Biochemistry, Genetics and Molecular Biology 6 2%
Other 21 8%
Unknown 108 39%
Attention Score in Context

Attention Score in Context

This research output has an Altmetric Attention Score of 29. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 10 March 2023.
All research outputs
of 26,075,497 outputs
Outputs from Cochrane database of systematic reviews
of 13,184 outputs
Outputs of similar age
of 332,506 outputs
Outputs of similar age from Cochrane database of systematic reviews
of 261 outputs
Altmetric has tracked 26,075,497 research outputs across all sources so far. Compared to these this one has done particularly well and is in the 94th percentile: it's in the top 10% of all research outputs ever tracked by Altmetric.
So far Altmetric has tracked 13,184 research outputs from this source. They typically receive a lot more attention than average, with a mean Attention Score of 34.6. This one has done well, scoring higher than 78% of its peers.
Older research outputs will score higher simply because they've had more time to accumulate mentions. To account for age we can compare this Altmetric Attention Score to the 332,506 tracked outputs that were published within six weeks on either side of this one in any source. This one has done particularly well, scoring higher than 91% of its contemporaries.
We're also able to compare this research output to 261 others from the same source and published within six weeks on either side of this one. This one has gotten more attention than average, scoring higher than 74% of its contemporaries.