Multivitamin supplementation and risk of birth defects

It is widely accepted that supplementation with folic acid, a B vitamin, re duces the risk of neural tube defects (NTDs). This case-control study teste d the hypothesis that multivitamins reduce risks of selected birth defects other than NTDs. Infants with and without birth defects and aborted fetuses with birth defects were ascertained in the greater metropolitan areas of B oston, Philadelphia, and Toronto during 1993-1996. Mothers were interviewed within 6 months after delivery about a variety of factors, including detai ls on vitamin use. Eight case groups were included: cleft lip with or witho ut cleft palate, cleft palate only, conotruncal defects, ventricular septal defects, urinary tract defects, limb reduction defects, congenital hydroce phaly, and pyloric stenosis (n's ranged from 31 to 186). Controls were 521 infants without birth defects (nonmalformed controls) and 442 infants with defects other than those of the cases (malformed controls). Daily multivita min supplementation was evaluated according to gestational timing categorie s, including periconceptional use (28 days before through 28 days after the last menstrual period). Odds ratios (ORs) below 1.0 were observed for all case groups except cardiac defects, regardless of control type. For pericon ceptional use, ORs with 95% confidence intervals that excluded 1.0 were est imated for limb reduction defects using both nonmalformed controls (OR = 0. 3) and malformed controls (OR = 0.2) and for urinary tract defects using bo th nonmalformed controls (OR = 0.6) and malformed controls (OR = 0.5). Stat istically significant ORs for use that began after the periconceptional per iod were observed for cleft palate only and urinary tract defects. These da ta support the hypothesis that periconceptional vitamin supplementation may extend benefits beyond a reduction in NTD risk. However, other than folic acid's protecting against NTDs, it is not clear what nutrient or combinatio n of nutrients might affect risk of other specific defects.