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Trends in Spina Bifida and Anencephalus in the United States, 1991-2002

by T. J. Mathews, M.S.

In 1992 the U.S. Public Health Service recommended that women of childbearing age increase consumption of the vitamin folic acid to reduce spina bifida and anencephalus. In 1996 the U.S. Food and Drug Administration authorized that all enriched cereal grain products be fortified with folic acid with an optional period starting in March 1996 with mandatory fortification beginning January 1998.  The 1999 National Health and Nutrition Examination Survey released results showing that these public health actions have been effective in increasing folate status among U.S. women of childbearing age (MMWR, October 27, 2000).

Birth certificate data in the United States have been available for selected birth defects since 1989 from the National Vital Statistics System, a component of the Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS).  This Health e-stat provides a 12-year trend for two neural tube defects, spina bifida and anencephalus.

After a significant increase in the spina bifida rate from 1992 to 1995 there was a significant decline from 1995 to 1999.  The rate was stable from 1999 to 2002. The rates for 1999, 2000, 2001, and 2002 were significantly lower than in 1997.  The rate of spina bifida in 2002 was 20.13 per 100,000 live births.

After a decline in the early part of the decade the anencephalus rate was stable during the mid-1990s (1994-97).  The rate of anencephalus in 2002 was 9.55 per 100,000 live births, significantly lower than in 1997. 

Birth certificate data for 1991-2002 are final. For further information about the birth data file see Births: Final Data for 2002. The numbers and rates for all years exclude data for Maryland, New Mexico, and New York, which in various years had either incomplete reporting or did not report these neural tube defects. The addition of Maryland and New York, which have fully reported both of these neural tube defects since 1996, has essentially no impact on the outcome of this analysis (data not shown).  Both spina bifida and anencephalus are considered underreported on the birth certificate.  CDC is continuing to monitor and analyze neural tube defect occurrence data.

Table 1.  Number of live births with spina bifida and rates per 100,000 live births for the United States, 1991-2002

Table 2.  Number of live births with anencephalus and rates per 100,000 live births for the United States, 1991-2002

Figure 1.  Spina bifida rates, 1991-2002

Figure 2.  Anencephalus rates, 1991-2002

This page last reviewed February 09, 2004