Why do we need this research?
Our body makes vitamin D from sunlight and it is also found in some foods. However, vitamin D deficiency is extremely common, and pregnant women and birthing people are at greatest risk. The UK Department of Health recommends that all pregnant people take vitamin D supplements in pregnancy to help their baby’s bones, teeth and muscles develop properly.
We know that low levels of vitamin D are linked with fertility problems and pregnancy complications such as pre-eclampsia and gestational diabetes, and research has shown that low-dose vitamin D supplements can help reduce the risk of these conditions. However, it has not been clear whether vitamin D levels are linked to the risk of miscarriage and recurrent miscarriage.
What is happening in this project?
To find out more, our researchers reviewed all previous studies that have been conducted by other research teams. They found 10 relevant studies, and when the results were combined, the team noticed a significant association between vitamin D levels and the risk of miscarriage or recurrent miscarriage – defined in this study as two or more miscarriages. In particular, the team found that women with low vitamin D levels are at significantly increased risk of miscarriage, while women who have experienced recurrent miscarriage are more likely to have a successful pregnancy if they have enough vitamin D.
Our researchers also wanted to find out whether vitamin D treatment before pregnancy could reduce the risk of miscarriage, but unfortunately this was not possible due to the limited number of studies on this topic and concerns about the quality of the data. Instead, the team will carry out a clinical trial in which women with a history of recurrent pregnancy loss will be tested for vitamin D deficiency prior to pregnancy so that they can receive treatment when necessary. This study will be carried out using a ‘cohort multiple randomised clinical trial’ – or cmRCT – design, and women in the large Tommy’s Net database will be randomly selected to take part.
What difference will this project make?
If our clinical trial shows that a ‘test and treat’ strategy for vitamin D deficiency improves the chances of having a successful live birth, this could pave the way for vitamin D testing and treatment to be offered routinely to women and birthing people who are most at risk.