With prevalences of 10-15 per 10 000 and 20 per 10 000 live births, neural tube defects and oral clefts are among the most common congenital malformations. Good evidence shows that periconceptional supplementation with folic acid reduces the risk of neural tube defects.12 What is less clear is the effect of folic acid supplementation on other birth defects, such as cleft lip, with or without cleft palate.

In this week's BMJ, Wilcox and colleagues3 report a population based case-control study from Norway, which shows that supplementation with folic acid in the periconceptional period reduces the risk of cleft lip, with or without cleft palate, in newborns. Supplementation with 400µg of folic acid for three months around conception was associated with a 40% reduction in the prevalence of cleft lip, with or without cleft palate, at birth (adjusted odds ratio 0.61, 95% confidence interval 0.39 to 0.96). Exposure data were obtained retrospectively one year after conception, but the reliability of the data …