Researchers have been examining the health impacts of folic acid supplements on pregnant women, and have found no evidence that they affect the occurrence rate of miscarriage.

The study, which was detailed in this week's edition of the Lancet journal (358: pp 796-800), was carried out by Jacqueline Gindler and colleagues at the Centres for Disease Control (CDC) in Atlanta and at the Beijing University's Health Science Centre.

Many women take folic acid before and during early pregnancy to reduce their chances of having a baby with a neural tube defect (NTD), and the study's participants were women in China who had registered in a recent folic acid campaign to prevent NTDs before becoming pregnant for the first time.

The researchers examined the risk of miscarriage in these women, who daily took pills containing only 400 µg of folic acid as part of the campaign and compared the results with a group of women who were similar in terms of, but who had not taken any supplements.

Overall, 9.1% of women suffered with a miscarriage, but the rates for women who had and who had not taken supplements were 9.0% and 9.3% respectively. The gestational age at pregnancy diagnosis and miscarriage were also very similar for both groups of women. This led the scientists to conclude that there is no evidence that the consumption of 400 µg of folic acid every day before and during early pregnancy influenced the risk of miscarriage.