Investigation of a cluster of anencephaly and spina bifida.

Environmental factors remain undefined as possible causes of spina bifida and anencephaly. The authors noted a fivefold increased incidence for 1979-1980 in the Antioch-Pittsburg , California area, prompting a case-control study. They studied nine case and 27 control mothers as well as eight case and 17 control fathers to evaluate factors including residence, occupation, drug use, illnesses, and pesticide or chemical exposure. Except for fathers' smoking (p less than 0.05), no exposure was associated with neural tube defects.