How effective are vitamin supplements in preventing miscarriage?
Many of the trials included in the review were not of high quality, either due to poor or unclear allocation concealment, or large losses to follow-up, which increased the risk of bias in the results. The data were also complicated by differing definitions of miscarriage. Other studies did not specify their definition of miscarriage or stillbirth. No trials reported on any potential psychological effects, such as anxiety and depression.
Poor diet with insufficient vitamins has been associated with an increased risk of miscarriage in early pregnancy. This has prompted investigation of the use of vitamin supplements prior to pregnancy or in early pregnancy to reduce the risk of miscarriage.