DRUG AND ENVIRONMENTAL-FACTORS ASSOCIATED WITH ADVERSE PREGNANCY OUTCOMES PART II - IMPROVEMENT WITH FOLIC-ACID

OBJECTIVE: TO provide a comprehensive review of periconceptional folic acid supplementation and factors affecting folate supplementation tri als. DATA SOURCES: A MEDLINE search was conducted through December 199 7. Additional sources were obtained from Current Contents and citation s from the references obtained. Search terms included folate, folic ac id, neural tube defect, spina bifida, and anencephaly. STUDY SELECTION : Relevant animal and human studies examining the effects of folate we re reviewed. DATA EXTRACTION: Data collected included: type of study, folate dosing, dietary folate intake, serum and red blood cell folate concentrations, type of defect(s) studied, vitamin usage, parental ris k factors, factors affecting trial results. DATA SYNTHESIS: Nine key f actors have been identified that affect outcomes of folic acid supplem entation trials. Daily doses of 0.8 mg decreased the occurrence and do ses of 4 mg decreased the recurrence of neural tube defects in randomi zed clinical trials. Since lower folic acid doses were effective in no nrandomized trials, research is needed to determine the lowest effecti ve dosage. Other benefits involving pregnancy outcome are suggested. C ONCLUSIONS: Women of childbearing age should take a daily folic acid s upplement to reduce the risk of pregnancies resulting in infants with a neural tube defect and other potential adverse pregnancy outcomes. F urther health benefits from folic acid supplementation are reviewed in Part III of this series.