Periodic health examination, 1994 update: 3. Primary and secondary prevention of neural tube defects. Canadian Task Force on the Periodic Health Examination.

OBJECTIVE: To make recommendations on nutritional interventions and screening manoeuvres to prevent the birth of infants with neural tube defects (NTDs).

OPTIONS: Folic acid consumption through diet or supplementation in women at low risk and at high risk of having a fetus with an NTD, and maternal serum alpha-fetoprotein (MSAFP) screening in low-risk pregnancies.

OUTCOMES: A reduction in the incidence rate of NTDs and potentially harmful effects of false-positive results of screening tests (i.e., abortion of a normal fetus).

EVIDENCE: A MEDLINE search with the use of medical subject headings "neural tube defects," "prenatal diagnosis" and "prevention and control" identified 103 original articles published between January 1979 and March 1993. Two reviewers extracted the data by applying the rules of evidence developed by the 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 effects 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% when 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 advised to increase their consumption of folic acid through diet or supplementation 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 recommendations of the US Centers for Disease Control and Prevention, the Society of Obstetricians and Gynaecologists of Canada, the Canadian Laboratory Centre for Disease Control and the Canadian College of Medical Geneticists, and they were validated through external review.

SPONSOR: These guidelines were developed and endorsed by the Canadian task force, which funded by Health Canada.