Vitamin D supplementation during pregnancy: Updated meta-analysis on maternal outcomes

- Supplementing pregnant women with vitamin D significantly increases 25(OH)D at term but results were inconsistent.
- It is unknown at this point what is the clinical significance of this finding but there is some indication that vitamin D supplementation, with or without calcium, may reduce the risk of pre-eclampsia.
- More studies are needed to confirm these results and to determine the effects of vitamin D supplementation on the risk of other maternal outcomes, such as gestational diabetes, impaired glucose tolerance, caesarean section, gestational hypertension, other adverse conditions and maternal death.

BackgroundVitamin D deficiency is highly prevalent during pregnancy. It has been suggested that vitamin D supplementation during pregnancy may reduce the risk of adverse gestational outcomes.ObjectivesTo update a previous meta-analysis on the effects of oral vitamin D supplementation (alone or in combination with other vitamins and minerals) during pregnancy on maternal 25(OH)D levels and risk of developing pre-eclampsia, gestational diabetes, preterm birth, impaired glucose tolerance, caesarean section, gestational hypertension and other adverse conditions.MethodsWe searched for randomized and quasi-randomized trials through the Cochrane Pregnancy and Childbirth Group's Trials Register, the International Clinical Trials Registry Platform, the Networked Digital Library of Theses and Dissertations, and direct communications with relevant organizations. Assessments of inclusion criteria, extraction of data from included studies, and risk of bias' assessments of the included studies were done independently by two review authors.ResultsWe included 15 trials, excluded 27 trials and 23 trials are still ongoing/unpublished. Data from seven trials with 868 women suggest that pregnant women supplemented with vitamin D had significantly higher 25(OH)D levels compared to controls (mean difference: 54.7 nmol/L; 95% CI 36.6, 72.9). Two trials found a lower risk of preeclampsia (8.9% versus 15.5%; average risk ratio 0.52; 95% CI 0.25, 1.05) and two other trials found no difference in the risk of gestational diabetes with vitamin D supplementation. Also, three trials found that supplementation with vitamin D plus calcium reduced the risk of pre-eclampsia (5% versus 9%; average risk ratio 0.51; 95% CI 0.32, 0.80).ConclusionSupplementing pregnant women with vitamin D led to significantly higher levels of 25(OH)D at term compared to placebo/control but results were inconsistent. Vitamin D supplementation, with or without calcium, may be related to lower risk of preeclampsia but more studies are needed to confirm this.