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.

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.

Are encephaloceles neural tube defects?

OBJECTIVE: Encephalocele is classified as a neural tube defect, but questions have been raised regarding whether its epidemiological characteristics are similar to those of other neural tube defects. DESIGN: We compared characteristics of temporal trends in, and the impact of folic acid grain fortification on, the prevalence of encephalocele, spina bifida, and anencephaly using data from the Metropolitan Atlanta Congenital Defects Program, a population-based birth defects surveillance system. Prevalences of encephalocele, spina bifida, and anencephaly were compared by maternal age, gender, race, birth weight, ascertainment period (1968-1981, 1982-1993, or 1994-2002), and fortification period (1994-1996 [prefortification] and 1998-2002 [postfortification]) using prevalence ratios with 95% confidence intervals. Temporal trends were assessed using Poisson and negative binomial regression models. RESULTS: Prevalence rates of encephalocele (n = 167), spina bifida (n = 650), and anencephaly (n = 431) were 1.4, 5.5, and 3.7 per 10 000 live births, respectively. Encephalocele was similar to anencephaly in showing an increased prevalence among girls and multiple gestation pregnancies and to spina bifida and anencephaly in an annual prevalence decrease between 1968 and 2002 (-1.2% for encephalocele, -4.2% for spina bifida, and -3.6% for anencephaly). With fortification, prevalence decreased for spina bifida but not significantly for encephalocele or anencephaly. CONCLUSIONS: Encephalocele shows more similarities to spina bifida or anencephaly than it shows differences with respect to characteristics, temporal trend, and impact of fortification. Additional studies should be done to explore the etiologic heterogeneity of encephalocele using better markers of folate status and a wider range of risk factors.