Vitamin D deficiency is extremely common, and pregnant women are more likely to be deficient. It's recommended that all pregnant people take vitamin D supplements in pregnancy to help their baby’s bones, teeth, and muscles develop.
We also know that low levels of vitamin D are linked with other serious pregnancy problems, including problems conceiving and pregnancy complications such as pre-eclampsia and preterm birth. Research has shown that taking a low dose vitamin D supplement can help reduce the risk of these conditions.
Yet it has long been unclear whether an early, low-cost, vitamin D treatment could also protect against pregnancy loss, including for women and pregnant people at high risk of recurrent miscarriage.
A review by our scientists at the Tommy's National Centre for Miscarriage Research in Birmingham, published in the journal Fertility and Sterility on 28 May, analysed all studies conducted by other research teams.
They evaluated whether these studies found a significant association between vitamin D levels and the risk of miscarriage or recurrent miscarriage.
The review found that women with low vitamin D levels are at significantly increased risk of miscarriage.
The authors also investigated whether treating vitamin D deficiency before conceiving protects against pregnancy loss in women at risk of miscarriage and if the timing of vitamin D assessment and treatment or the vitamin D dose changes miscarriage risk.
Because of the limited number of studies on this topic the authors were unable to confirm that vitamin D supplementation reduces the risk of miscarriage.
Our research team recommend that future vitamin D studies investigate whether vitamin D treatment helps to protect against pregnancy loss by enhancing vitamin D levels before conception.
Why is Vitamin D important in pregnancy?
Lead author Dr Jennifer Tamblyn, who is based at the Tommy's National Centre for Miscarriage Research says:
“We know vitamin D is essential for bone development in the developing baby. The placenta also produces large amounts of the active form of vitamin D. There is research showing an important role for vitamin D in early pregnancy, including regulation of maternal-fetal immune responses and blood vessel development, which are important for a healthy pregnancy.
“Vitamin D is safe and low cost, so from a public health approach supplements are a great recommendation. Unfortunately, we know that in the UK the uptake of women and pregnant people taking antenatal vitamin supplements remains low at around 20%.
“Vitamin D has only really been known for its role in late pregnancy complications but our review supports another important role for it too, which could help encourage women about the benefits of taking supplements early.
“We believe that more research is needed so healthcare practitioners have a clearer, evidence-based strategy for recommending vitamin D supplementation to pregnant women and those planning a pregnancy.”
'Vitamin D and miscarriage: a systematic review and meta-analysis' is available to read in the journal Fertility and Sterility (open access)