While nutritional advice for pregnant women is no longer to ‘eat for two’, it is important to consider nutritional status, as vitamin D deficiency or insufficiency may develop during pregnancy.

However, Cochrane researchers have suggested that the question of supplementation is not as straightforward as it may seem.¹⁰

They analysed 15 randomised controlled trials involving 2,833 women, with nine of the trials considering the effect of vitamin D on its own and six considering vitamin D with calcium supplementation. Supplementation clearly improved vitamin D levels measured as 25-hydroxyvitamin D concentrations at the time of giving birth.

Benefits appear to include a potentially reduced risk of delivering a baby prematurely (ie, before 37 weeks), a lower risk of high blood pressure in the mother, and a reduced risk of a low birth weight for the baby (ie, less than 2.5kg). “However, it appears that when vitamin D and calcium are combined, the risk of preterm birth is increased,” says the review.

Due to the relatively small amount of data, the researchers advise that the clinical significance is unclear, and to interpret the results with caution.

“With the available evidence, it is unclear whether vitamin D supplementation should be given as part of routine antenatal care to improve maternal and infant outcomes.” However, there is some indication that vitamin D supplementation could reduce the risk of pre-eclampsia and increase body length and head circumference at birth, but more studies are needed.

In its consideration of the Healthy Start scheme, NICE had found a lack of quality of life data around vitamin D deficiency. While there was an impact from folic acid, NICE said that, while there would be some cost savings from Healthy Start due to reducing the need to treat vitamin D deficiency, the savings would be relatively small.⁷