Early childhood surveillance of developmental disorders by a birth defects surveillance system: methods, prevalence comparisons, and mortality patterns.

The prevalence of developmental disabilities in early childhood is not well documented. An established birth defects registry extended surveillance to identify cases of developmental disorders in early childhood by adding all known sources of diagnosis and service to case-finding methods. Residents of a northwest Arkansas region born during 1985 to 1987 and diagnosed with either a birth defect or a developmental disorder by the 4th birthday comprised the studied cohort. Case records were linked with death certificates to examine the influence of mortality on prevalence ratios. Prevalence ratios estimated were 64.5/1000 resident live births (60.9/1000 among survivors to age 4 years) for either birth defect or developmental disorder, 33.4/1000 for developmental disorder, 37.0/1000 for birth defect, and 9.5/1000 for both developmental disorder and birth defect. Prevalence ratios of specific developmental disorders and the role of mortality in decreasing population prevalence are reported. The most common diagnostic categories in this age group were developmental delay, seizures, and failure to thrive. Overlap of birth defect categories with a diagnosed developmental disability was examined; 68.8% of children diagnosed with neural tube defects and 45.5% of those with chromosomal abnormalities who survived to age 4 years had clinically diagnosed developmental disorders. An anticipated high degree of overlap (77%) for other central nervous system defects was found. For other birth defect categories, developmental disorder diagnosis was present in 20 to 30% of the study group. Death before age 4 years occurred most often when the diagnosis was newborn seizures (17.1%) or "conditions of the brain" (13.6%); the mortality rate was 6 to 8% for epilepsy or seizure disorders, mental retardation, and vision loss. The large number of developmental diagnoses among this cohort indicates that surveillance of these disorders in early childhood, even with tentative diagnoses, is feasible. Data obtained indicate that many birth defects are associated with developmental disorders; potentially, this association can contribute to earlier identification of developmental disorders in childhood.