Lack of vitamin D linked to lower birth rates after fertility treatment

Women who had fertility treatments were a third less likely to deliver a baby if they had low levels of vitamin D compared with women who sufficient vitamin D, a review study has found.

Researchers at the University of Birmingham analysed 11 studies, with data from 2700 women who had received fertility treatment and had their vitamin D levels tested. The researchers also found that women with enough vitamin D were more likely to have a clinical pregnancy (where a fetal heart beat could be detected) or a positive pregnancy test. There was no association between miscarriage and vitamin D levels.

'Although an association has been identified, the beneficial effect of correction of vitamin D deficiency or insufficiency needs to be tested by performing a clinical trial,' said Dr Justin Chu, study lead author at the University of Birmingham and Birmingham Women's and Children's NHS Foundation Trust.

The major source for vitamin D is sunlight. It is also found in foods such as oily fish, red meat and liver, and can be taken as a supplement. However, is not clear if taking vitamin D supplements can increase women's chances of having a child after assisted conception.

'Women who want to achieve a successful pregnancy should not rush off to their local pharmacy to buy vitamin D supplements until we know more about its effects,' said Dr Chu. 'It is possible to overdose on vitamin D and this can lead to too much calcium building up in the body, which can weaken bones and damage the heart and kidneys.'

A limitation of the study was that that vitamin D levels were assessed before fertility treatment in some studies and at the time of egg collection in other studies. The 11 studies analysed were also quite diverse, studying women who had a range of fertility treatments including IVF, intracytoplasmic sperm injection or frozen embryo transfer.

The research did not explore the mechanism for how vitamin D might affect pregnancy. The scientists suggest that vitamin D could affect the ability of the embryo to implant in the womb lining. They are now calling for a large, randomised control trial to look at whether vitamin D supplements could improve birth rates in women undergoing assisted reproduction.

The study was published in the journal Human Reproduction.