RT Journal Article SR Electronic T1 Neural tube defects and periconceptional folic acid JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP 255 OP 256 VO 167 IS 3 A1 Rezan A. Kadir A1 Demetrios L. Economides YR 2002 UL http://www.cmaj.ca/content/167/3/255.abstract