Effect of taking extra calcium (other than preventing or treating high blood pressure) during pregnancy for improving maternal and infant health

Maternal nutrition during pregnancy is known to have a significant effect on fetal growth and development. In our review, regular intake of extra calcium tablets during pregnancy did not improve the number of preterm births or other infant outcomes, except for a slight increase in infant birthweight in the group of women who received calcium supplementation. Most studies included in this review were assessed as of low risk of bias, and evidence for specific outcomes was graded as of moderate quality, Taking calcium supplementation did not appear to have any obvious side effects. Our review included 25 randomised controlled studies, but only 23 studies involving 18,587 women contributed outcome data. The majority of the evidence was based on fewer numbers of studies.

Authors' conclusions: 

This review indicates that there are no clear additional benefits to calcium supplementation in prevention of preterm birth or low infant birthweight. While there was a statistically significant difference of 56 g identified in mean infant birthweight, there was significant heterogeneity identified, and the clinical significance of this difference is uncertain.

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Maternal nutrition during pregnancy is known to have an effect on fetal growth and development. It is recommended that women increase their calcium intake during pregnancy and lactation, although the recommended dosage varies among professionals. Currently, there is no consensus on the role of routine calcium supplementation for pregnant women other than for preventing or treating hypertension.


To determine the effect of calcium supplementation on maternal, fetal and neonatal outcomes (other than for preventing or treating hypertension) as well as any possible side effects.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30th September 2014).

Selection criteria: 

We considered all published, unpublished and ongoing randomised controlled trials (RCTs) comparing maternal, fetal and neonatal outcomes in pregnant women who received calcium supplementation versus placebo or no treatment. Cluster-RCTs were eligible for inclusion but none were identified. Quasi-RCTs and cross-over studies were not eligible for inclusion.

Data collection and analysis: 

Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy.

Main results: 

Twenty-five studies met the inclusion criteria, but only 23 studies contributed data to the review. These 23 trials recruited 18,587 women, with 17,842 women included in final analyses. There were no statistically significant differences between women who received calcium supplementation and those who did not in terms of reducing preterm births less than 37 weeks' gestation (risk ratio (RR) 0.86, 95% confidence interval (CI) 0.70 to 1.05; 13 studies, 16,139 women; random-effects model) or less than 34 weeks' gestation (RR 1.04, 95% CI 0.80 to 1.36; four trials, 5669). Most studies were of low risk of bias. We conducted sensitivity analysis for the outcome of preterm birth less than 37 weeks by removing two trials with unclear risk of bias for allocation concealment; the results then favoured treatment with calcium supplementation (RR 0.80, 95% CI 0.65 to 0.99; 11 trials, 15,379 women). There was no significant difference in infant low birthweight between the two treatment groups (RR 0.93, 95% CI 0.81 to 1.07; six trials, 14,162 infants; random-effects model). However, when compared to the control group, women in the calcium supplementation group gave birth to slightly heavier birthweight infants (mean difference 56.40, 95% CI 13.55 to 99.25; 21 trials, 9202 women; random-effects model).

Three outcomes were chosen for assessment with the GRADE software: preterm birth less than 37 weeks; preterm birth less than 34 weeks; and low birthweight less than 2500 g. Evidence for these outcomes was assessed as of moderate quality.