Prevalence of spina bifida and anencephaly during the transition to mandatory folic acid fortification in the United States.
BACKGROUND
In 1992, the United States Public Health Service recommended that all women of childbearing age consume 400 microg of folic acid daily. The Food and Drug Administration authorized the addition of synthetic folic acid to grain products in March 1996 with mandatory compliance by January 1998. The impact of these public health policies on the prevalence of neural tube defects needs to be evaluated. We sought to determine the prevalences of spina bifida and anencephaly during the transition to mandatory folic acid fortification.


METHODS
Twenty-four population-based surveillance systems were used to identify 5,630 cases of spina bifida and anencephaly from 1995-99. Cases were divided into three temporal categories depending on whether neural tube development occurred before folic acid fortification (January 1995 to December 1996), during optional fortification (January 1997 to September 1998), or during mandatory fortification (October 1998 to December 1999). Prevalences for each defect were calculated for each time period. Data were also stratified by programs that did and did not ascertain prenatally diagnosed cases.


RESULTS
The prevalence of spina bifida decreased 31% (prevalence ratio [PR] = 0.69, 95% confidence interval [CI] = 0.63-0.74) from the pre- to the mandatory fortification period and the prevalence of anencephaly decreased 16% (PR = 0.84, 95% CI = 0.75-0.95). Stratification by prenatal ascertainment did not alter results for spina bifida but did impact anencephaly trends.


CONCLUSIONS
The decline in the prevalence of spina bifida was temporally associated with folic acid fortification of US grain supplies. The temporal association between fortification and the prevalence of anencephaly is unclear.
National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia 30341, USA. lnw9@cdc.gov
Laura J
LJ
Williams
Cara T
CT
Mai
Larry D
LD
Edmonds
Gary M
GM
Shaw
Russell S
RS
Kirby
Charlotte A
CA
Hobbs
Lowell E
LE
Sever
Lisa A
LA
Miller
F John
FJ
Meaney
Miriam
M
Levitt
D000757:Anencephaly / Q000453:epidemiology* / Q000517:prevention & control; D005492:Folic Acid / Q000494:pharmacology*; D005527:Food, Fortified; D006801:Humans; D015201:Meta-Analysis as Topic; D015995:Prevalence; D011634:Public Health; D016135:Spinal Dysraphism / Q000453:epidemiology* / Q000517:prevention & control; D014481:United States / Q000453:epidemiology
D005492:Folic Acid