Improved ascertainment of cardiovascular malformations in infants with Down's syndrome, Atlanta, 1968 through 1989. Implications for the interpretation of increasing rates of cardiovascular malformations in surveillance systems.

Abstract

Several birth defects surveillance systems have shown an upward trend in the birth prevalence of several congenital cardiovascular malformations. Improvements in clinical ascertainment have been suggested as an explanation for this increase. For several decades, 40-50% of infants with Down's syndrome have been reported to have cardiac defects associated with the unbalanced genotype. Therefore, secular changes in the frequency of ascertained cardiovascular malformations among infants with Down's syndrome in surveillance systems could shed light on improvements in the ascertainment of these defects. The authors examined changes in the frequency of ascertained cardiovascular malformations among 532 cases of Down's syndrome recorded in the Metropolitan Atlanta Congenital Defects Program from 1968 through 1989. Overall, 33% of the cases have reported cardiovascular malformations. However, the frequency of these defects in Down's syndrome infants increased dramatically from about 20% in the early 1970s to more than 50% in the late 1980s (p = 0.0001). This upward trend was seen for all major categories of cardiac defects and persisted after the cases were stratified by race, sex, maternal age, hospital of birth, birth weight, and gestational age. These results show improvement in the ascertainment of cardiovascular malformations among Down's syndrome infants in a surveillance population. They are also consistent with the hypothesis that the increasing rates of cardiac defects are related, at least in part, to improved ascertainment of these defects in the population.