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Prevalence of birth defects among low-birth-weight infants. A population study.

Major birth defects are diagnosed in about 3% to 4% of infants during their first year of life. Because many infants with birth defects have intrauterine growth retardation, are born prematurely, or both, the rate of birth defects undoubtedly varies according to the infant's birth weight. Nevertheless, the magnitude of such variation has not, to our knowledge, been adequately studied in well-defined populations. We analyzed data from the population-based Metropolitan Atlanta (Ga) Congenital Defects Program for 1978 through 1988. These data included information on 11,398 infants who were diagnosed with serious birth defects among 317,499 singleton live-born infants. Although the overall rate of birth defects was 3.6%, we observed a striking inverse relationship between the birth defects rate and the infants' birth weights. The birth defect rates were 16.2% for newborns weighing less than 1500 g at birth, 13.2% for newborns weighing from 1500 g to 1999 g, 6.2% for newborns weighing from 2000 g to 2499 g, 3.2% for newborns weighing from 2500 g to 3999 g, and 2.8% for newborns weighing 4000 g or more. Analyses by type of defect indicated that most birth defects were significantly associated with low birth weight. The higher risk of birth defects among low-birth-weight infants demonstrates that birth defects contribute to excess morbidity among low-birth-weight infants. Because of the overlap between birth defects and low birth weight, the prevention of low birth weight in the population depends greatly on a better recognition of the complex etiology of low birth weight and, in part, on the delineation of risk factors that influence the occurrence of birth defects.