Vitamin D deficiency linked to higher risk of miscarriage

Women with low vitamin D levels are at significantly increased risk of miscarriage, a new study reveals.

Scientists say that assessing vitamin D levels and treating deficiency before conception may offer greater benefit compared to only taking vitamin D during the first trimester – but call for more research to confirm this approach.

Led by experts at the University of Birmingham, the research team at Tommy's National Centre for Miscarriage Research evaluated every study into the impact of Vitamin D during pregnancy - finding a significant association between vitamin D levels and the risk of miscarriage or recurrent miscarriage.

The team also looked at whether vitamin D supplementation reduces the risk of miscarriage, and if the timing of vitamin D assessment, treatment or dose changes miscarriage risk - publishing their findings in Fertility & Sterility.

Lead author Dr Jennifer Tamblyn, from the Institute of Metabolism and Systems Research at the University of Birmingham, commented: “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 deficiency is extremely common, and pregnant women are more likely to be deficient. All pregnant women are recommended to take vitamin D supplements in pregnancy to help their baby’s bones, teeth, and muscles develop.

It is now clear that the role of vitamin D is much wider, with low levels linked with other serious pregnancy problems including problems conceiving, and pregnancy complications such as pre-eclampsia and preterm birth. Research has already shown that taking a low dose vitamin D supplement can help reduce the risk of these conditions.

The authors investigated whether treating vitamin D deficiency before conceiving protects against pregnancy loss in women at risk of miscarriage. However, 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.

Considering why vitamin D may be important in pregnancy, it is essential for bone development in the developing baby. The placenta also produces large amounts of the active form of vitamin D and there is research showing an important role for vitamin D in early pregnancy, including regulation of maternal-foetal immune responses and blood vessel development, which are important for a healthy pregnancy.