Evaluation of the hospital discharge diagnoses index and the birth certificate as sources of information on birth defects.

The hospital discharge diagnoses index (DI) for newborns and the birth certificate were evaluated as sources of information about birth defects by comparing them with the same births in the case registry of the California Birth Defects Monitoring Program (CBDMP). The CBDMP is an active surveillance system; the staff visit hospitals to identify children with birth defects diagnosed in the first year of life. The study population comprised 66,481 live births to residents of five counties in the San Francisco Bay area in 1983. Of these infants, 2,543 had at least one birth defect noted on the DI, and 1,623 were in the CBDMP registry; 1,020 with defects noted on the DI were also in the CBDMP registry. For this same population, 399 infants had one or more defects noted on the birth certificate; 304 of these were also in the CBDMP registry. Reporting of birth defects on the birth certificate was poor for every condition. Reporting on the DI was most reliable for oral clefts and chromosomal defects; for these defects, the DI omitted one-third of the cases but had identified only about 10 percent false-positive (that is, unverified) cases. Major central nervous system malformations were less well reported, with about one-third of them false-positive. For all other birth defects, the DI either omitted more than half of the cases, or more than half of the cases reported were false-positive cases. These findings raise questions about the validity of analytic studies of birth defects if the data are obtained only from the DI or the birth certificate.