PERIODIC HEALTH EXAMINATION, 1994 UPDATE .3. PRIMARY AND SECONDARY PREVENTION OF NEURAL-TUBE DEFECTS

Objective: To make recommendations on nutritional interventions and sc reening manoeuvres to prevent the birth of infants with neural tube de fects (NTDs). Options: Folic acid consumption through diet or suppleme ntation in women at low risk and at high risk of having a fetus with a n NTD, and maternal serum alpha-fetoprotein (MSAFP) screening in low-r isk pregnancies. Outcomes: A reduction in the incidence rate of NTDs a nd potentially harmful effects of false-positive results of screening tests (i.e., abortion of a normal fetus). Evidence: A MEDLINE search w ith the use of medical subject headings ''neural tube defects,'' ''pre natal diagnosis'' and ''prevention and control'' identified 103 origin al articles published between January 1979 and March 1993. Two reviewe rs extracted the data by applying the rules of evidence developed by t he Canadian Task Force on the Periodic Health Examination. Values: The task force's evidence-based methods and values were used; high value was placed on prevention of NTDs and on limitation of the harmful effe cts of a pregnancy involving a fetus with an NTD. Benefits, harms and costs: Evidence suggests that folic acid supplementation can decrease the incidence rate of NTDs in low-risk pregnancies by 40% to 60% with no adverse effects. MSAFP screening between the 16th and 18th weeks of gestation can reach a sensitivity of 83% and a specificity of 98% whe n it is used as part of an organized program. The effect of screening on the incidence rate of NTDs depends on whether affected fetuses are aborted. Recommendations: All women of childbearing age should be advi sed to increase their consumption of folic acid through diet or supple mentation to 0.4 mg/d beginning 1 month before pregnancy and ending at the start of the second trimester. MSAFP screening is recommended in low-risk pregnancies only when it is part of a screening program that includes access to all necessary diagnostic services. High-risk women should be referred to genetic counselling before they plan a pregnancy . Validation: These recommendations are comparable to the current reco mmendations of the US Centers for Disease Control and Prevention, the Society of Obstetricians and Gynaecologists of Canada, the Canadian La boratory Centre for Disease Control and the Canadian College of Medica l Geneticists, and they were validated though external review. Sponsor : These guidelines were developed and endorsed by the Canadian task fo rce, which is funded by Health Canada.