Vitamin D is produced by the human body from exposure to sunlight and can also be consumed from foods such as fish-liver oils, fatty fish, mushrooms, egg yolks, and liver. Vitamin D has many functions in the body; it helps maintain bone integrity and calcium homeostasis.
During pregnancy, vitamin D deficiency or insufficiency may develop. Vitamin D supplementation during pregnancy has been suggested to safely improve pregnancy and infant outcomes. This review included six randomised controlled trials. Five trials involving 623 women compared the effects of vitamin D alone versus no supplementation or a placebo and one trial with 400 women compared the effects of vitamin D and calcium with no supplementation.
The results show that the provision of vitamin D supplements during pregnancy improves the women’s vitamin D levels, as measured by 25-hydroxyvitamin D levels, at term. However, the clinical significance of this finding is yet to be determined as there is no evidence that vitamin D supplementation prevents pre-eclampsia, gestational diabetes, impaired glucose tolerance, caesarean section, gestational hypertension, or death in the mothers; or preterm birth, stillbirth, neonatal death, neonatal admission to intensive care unit, newborns with low Apgar score or neonatal infection.
Data from three trials involving 463 women show a trend for women who receive vitamin D supplementation during pregnancy to less frequently have a baby with a birthweight below 2500 grams than those women receiving no treatment or placebo, although the statistical significance was borderline.
The number of trials and outcomes reported are too limited, and in general are of low quality, to draw conclusions on the usefulness and safety of this intervention as a part of routine antenatal care. Further rigorous randomised trials are required to evaluate the role of vitamin D supplementation in pregnancy.