Maternal characteristics for 616 case families and 1,645 control families enrolled in National Birth Defects Prevention Study between 1997 and 2008.

Summary statistics were expressed as mean ± standard deviation for continuous variables, and frequency (percentage) for categorical variables.1Folic acid supplements yes is defined as maternal use of folic acid supplements at least two months during the exposure window (i.e. one month prior to conception and two months after conception).2Alcohol consumption yes is defined as drinking during the three months after pregnancy.3Tobacco use yes is defined as cigarette smoking during the three months after pregnancy.Maternal characteristics for 616 case families and 1,645 control families enrolled in National Birth Defects Prevention Study between 1997 and 2008.