title: Interpreting changes in the epidemiology of anencephaly and spina bifida following folic acid fortification of the U.S. grain supply in the setting of long-term trends, Atlanta, Georgia, 1968-2003.
abstract: BACKGROUND
  The prevalence of anencephaly (AN) and spina bifida (SB) was declining long before fortification of enriched grains in the U.S. with folic acid. We examined whether changes in these defects surrounding fortification could be distinguished from preexisting trends.
  
  
  METHODS
  We used data from the Metropolitan Atlanta Congenital Defects Program to identify three ascertainment periods: Period 1 (1968-1981), prenatal diagnoses rarely made; Period 2 (1981-1993), prenatal diagnoses made but not ascertained; Period 3 (1994-2003), prenatal diagnoses ascertained. We compared the annual percent change (APC) in AN and SB for each period using Poisson regression, then compared prevalences during each period for categories of pregnancy outcome, sex, race, gravidity, and maternal age.
  
  
  RESULTS
  The prevalence of AN (N = 434) and SB (N = 663) declined during 1968-2003. The APCs in Periods 1, 2, and 3, respectively, were -6.9%, -2.9%, and -6.8% for AN, and -7.1%, -7.0%, and -6.2% for SB; 95% confidence intervals around the APCs for Periods 2 and 3 overlapped for both defects. Prevalence ratios (PRs) for females relative to males decreased for AN (2.3 in Period 1; 1.2 in Period 3); PRs for whites relative to blacks or African Americans decreased for both AN (2.7 in Period 1; 1.2 in Period 3) and SB (2.5 in Period 1; 1.1 in Period 3).
  
  
  CONCLUSIONS
  Our analysis suggests that changes in AN and SB surrounding folic acid fortification (Period 3) could be part of preexisting trends. This must be considered when evaluating prevention efforts.
authors.affiliation: National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Lilah M
authors.initials: LM
authors.lastname: Besser
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Williams
authors.forename: Janet D
authors.initials: JD
authors.lastname: Cragan
mesh_terms: D000757:Anencephaly / Q000453:epidemiology* / Q000517:prevention & control; D005006:Ethnicity / Q000706:statistics & numerical data; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage*; D005527:Food, Fortified; D005845:Georgia / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008297:Male; D015995:Prevalence; D017678:Sex Distribution; D016135:Spinal Dysraphism / Q000453:epidemiology* / Q000517:prevention & control; D013997:Time Factors; D014481:United States / Q000453:epidemiology
chemical_list: D005492:Folic Acid