Further complicating this effect is the impact of folic acid supplementation; the study also stratified results by maternal folic acid‐containing vitamin supplementation and found that exposure to NO and the rs762551 variant of CYP1A2 resulted in a statistically significant odds ratio of 5.2 for spina bifida in non‐vitamin users while there was no such significantly increased risk of spina bifida in vitamin users.131. This evidence concerns the gene CYP1A2 and spina bifida.