Prevalence of spina bifida at birth--United States, 1983-1990: a comparison of two surveillance systems.

PROBLEM/CONDITION: Spina bifida is a birth defect of the spinal column that is a substantial contributor to serious developmental disabilities in the United States. The risk for spina bifida and other neural tube defects (NTDs) can be reduced if women consume 0.4 mg of folic acid before and during the first trimester of pregnancy. Public health programs are being developed to prevent many NTDs by increasing the consumption of folic acid by women of childbearing age. To assess the national impact of these programs on the prevalence of NTDs at birth, multistate surveillance is needed to monitor secular trends in birth-prevalence rates. This report summarizes a collaborative effort by CDC and state birth defect surveillance programs in 16 states to a) obtain multistate, population-based data concerning the birth prevalence and descriptive epidemiology of spina bifida and b) determine the usefulness of combining state surveillance data to monitor national trends in the birth prevalence of NTDs.

REPORTING PERIOD

This report presents data from birth defects surveillance systems in 16 states for the period 1983-1990 (specific periods covered varied by state). These findings are compared with CDC's Birth Defects Monitoring Program (BDMP) for the same period.

DESCRIPTION OF SYSTEMS

Population-based data about live-born and stillborn infants who have spina bifida were analyzed from 16 state programs. These 16 programs differed in size and racial/ethnic composition of the populations, surveillance methods, and completeness of case ascertainment. Hospital-based data about live-born and stillborn infants who have spina bifida also were analyzed from BDMP, a passive case ascertainment surveillance system that obtains data from participating hospitals in 50 states.

RESULTS AND INTERPRETATION

From 1983 through 1990, the birth-prevalence rate for spina bifida for the 16 states was 4.6 cases per 10,000 births; the BDMP rate was nearly identical (4.4 cases). State-specific rates varied substantially, ranging from 3.0 (Washington) to 7.8 (Arkansas). Both state-based and BDMP rates varied among racial/ethnic groups; in both systems, the rates were highest for Hispanics and lowest for Asians/Pacific Islanders. In both the state-based surveillance systems and BDMP, the annual rate of spina bifida for the total population declined during the period 1983-1990. Much of this decline can be attributed to increased prenatal diagnosis in the 1980s. However, because of decline in the rates of spina bifida and other NTDs in the United States began before the widespread availability of prenatal diagnostic services, an environmental component may have contributed substantially to the etiologies of these defects. The birth-prevalence rate of spina bifida was slightly higher among females than males. The ratio of female-to-male prevalence rates was 1.2 for both the state-based surveillance systems and BDMP. This ratio varied considerably among racial/ethnic groups and among states. The similarities of rates and trends in the birth prevalence of spina bifida between the state-based surveillance data and the BDMP data indicate that both types of surveillance systems can provide reliable information concerning national trends in the birth prevalence of spina bifida.

ACTIONS TAKEN

CDC and state birth defects surveillance programs will use results from this analysis to monitor national trends in the birth prevalence of spina bifida in the United States. Aggregated state-based surveillance data about spina bifida, anencephaly, and other NTDs will facilitate the monitoring of changes in NTDs after implementation of programs to increase folic acid consumption by women of childbearing age.