Calcium Supplementation for Improving Pregnancy and Infant Outcomes (Other Than for Preventing or Treating Hypertension)

Does calcium supplementation during pregnancy improve maternal and infant outcomes, other than preventing hypertensive disorders of pregnancy?

Calcium supplementation may slightly reduce preterm birth rates between 34 and 37 weeks' gestation, but it likely has little to no effect on preterm birth rates less than 34 weeks' gestation or on the risk of low birth weight (less than 2,500 g).¹ (Strength of Recommendation: B, inconsistent or limited-quality patient-oriented evidence.)

Maternal nutrition during pregnancy has significant effects on fetal growth and development.¹ The World Health Organization (WHO) recommends up to 2,000 mg of daily calcium supplementation, particularly in pregnant women with low dietary calcium intake, to reduce the risk of hypertensive disorders in pregnancy.^2,3 Recent studies showed that less than 1,000 mg of daily calcium supplementation was also effective.^4,5 However, the effect of calcium supplementation on other maternal and infant outcomes remains uncertain. The authors of this Cochrane review aimed to identify whether antepartum calcium supplementation reduces preterm birth and low birth weight risk.¹

This Cochrane review included 19 trials and 16,625 pregnant women.¹ The authors looked for randomized controlled trials demonstrating maternal, fetal, and neonatal outcomes in which pregnant patients received calcium supplementation compared with placebo or no treatment. Patients with multiple gestations or hypertension were excluded. Protocols varied, but in 17 of the 19 trials, high-dose calcium (greater than 1,000 mg/day) was prescribed, and in 14 studies, calcium carbonate was the most common form of calcium supplementation. The timing of calcium supplementation varied, with use continuing until delivery; in five studies, participants started calcium supplementation before 20 weeks' gestation, and in nine studies, participants started supplementation at 20 weeks' gestation. It is not clear what the baseline calcium intake or laboratory values were for trial participants. The trials were conducted across 13 different countries (ie, Argentina, Australia, Colombia, Egypt, Ecuador, Gambia, Guatemala, Hong Kong, India, Mexico, South Africa, the United States, Vietnam).

Calcium supplementation vs placebo or no treatment may have slightly reduced the risk of preterm birth at less than 37 weeks' gestation (relative risk [RR] = 0.80; 95% CI, 0.65–0.99).¹ Subgroup analysis demonstrated that beginning the use of calcium before 20 weeks' gestation did not change the effectiveness likelihood. Trial results were consistent, and the overall results were not swayed by any one large trial. Calcium supplementation had little to no effect on preterm birth before 34 weeks' gestation compared with placebo or no treatment.

Calcium supplementation had little or no effect on low birth weight compared with placebo or no treatment.¹ Subgroup analysis demonstrated that beginning calcium supplementation before 20 weeks' gestation did not increase the effectiveness likelihood in preventing low birth weight; however, meta-analysis of three studies in which calcium was started after 20 weeks' gestation demonstrated that supplementation appeared to slightly reduce the risk of low birth weight (RR = 0.41; 95% CI, 0.23–0.73; three studies; n = 737 patients). The data on low-dose calcium supplementation were insufficient to further investigate this effect.

This review found no evidence that calcium supplementation affected other outcomes (eg, maternal weight gain, maternal bone mineral density, maternal death, intrauterine growth restriction, perinatal mortality) or was associated with adverse outcomes such as gastrointestinal symptoms, gallstones, urinary stones, urinary tract infections, impaired kidney function, or maternal anemia.¹