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Temporal Trends in Reported Malformation Incidence for the United States - Birth Defects Monitoring Program

Godfrey P. Oakley, Jr., M.D. Levy M. James Larry D. Edmonds, M.S.P.H. Birth Defects Branch Chronic Diseases Division Center for Environmental Health

Introduction and Methods

Reports of increased occurrence of ventricular septal defects underscore the importance of monitoring trends in birth defects (1t). The Birth Defects Monitoring Program (BDMP) is a collaborative effort involving two governmental agencies and two private, nonprofit organizations: The National Institute of Child Health and Human Development, CDC, the March of Dimes Birth Defects Foundation, and the Commission on Professional and Hospital Activities (CPHA), Ann Arbor, Michigan (2-4t). Its primary purpose is to monitor the incidence of birth defects and other conditions of the newborn. Data used in this program are included in those already sent to CPHA as part of its Professional Activity Study (PAS) health-data-processing system. Discharge abstracts are coded by hospital medical records department staff and submitted regularly to CPHA for data processing. Included are abstracts on all live-born and stillborn infants delivered in each PAS hospital. Portions of the data contained in abstracts on the newborn are used in the BDMP, thus resulting in a monitoring system that involves no added hospital costs or reporting responsibilities. At CPHA these data are entered into a special data file and used to produce monitoring reports and other tabulations. These reports and tabulations for PAS hospitals that agree to participate in the BDMP are sent to CDC for analysis. A total of 161 defect categories are analyzed to determine increases or other unusual trends. Currently, data on 960,184 births in 1,128 hospitals are used in the BDMP.

Although this data source is not population-based and not a random sample of U.S. births, it nevertheless represents the largest single source of uniformly collected and coded discharge data on birth defects among newborns. Maternal data are not routinely available through this system. Although the BDMP functions primarily as an early warning system, it can be useful also for correlating incidence patterns with such trends as the temporal and geographic distribution of drugs, chemicals, and other possible human teratogens.

Results and Discussion

Noteworthy findings are the substantial unexplained increases in rates of ventricular septal defect (1t), patent ductus arteriosus, and renal agenesis (Table 1). Rh hemolytic disease incidence has substantially decreased because more females are receiving appropriate postpartum treatment and also because the average parity has decreased (Table 2). The decreases in anencephaly and spina bifida rates--two of the most common and serious environmental-associated birth defects--are unexplained and do not appear to reflect prenatal diagnosis (5t) (Table 2). The marked decrease in the incidence of anophthalmos occurred primarily between 1973 and 1974, coincident with a general coding change; however, it is not clear whether this is the cause of the decrease (Table 2). Down syndrome rates remained nearly constant over the decade, in spite of a decline from 6% to 5% in the proportion of births to females 4!535 years old (6t) (Table 3). Even though this is a high-risk group for Down syndrome, only a small proportion of births and cases occur among these females, and the observed change in crude incidence is almost exactly that expected as a result of this change in the maternal age distribution. The stability of congenital rubella in the face of a sharp decline in clinical rubella is surprising, and there is presently no explanation for the disparity (Table 3).

The BDMP data must be interpreted with care but, used as a screening tool, they frequently call attention to areas that need additional study. Variations in incidence may be caused by changes other than those associated with environmental teratogens--for example, chance, diagnostic habits, and reporting procedures. These possible explanations must be considered in seeking the cause of a trend or geographic cluster.

References

  1. Layde PM, Dooley K, Erickson JD, Edmonds LD. Is there an epidemic of ventricular septal defects in the U.S.? The Lancet 1980;1:407-8.

  2. Oakley GP Jr. Incidence and epidemiology of birth defects. In: Genetic issues in pediatrics and obstetric practice. Kaback MM ed. Chicago Year Book Medical Publishers, Inc., 1981:25-43.

  3. CDC. Congenital malformations surveillance report January-December 1980, issued February 1982, Atlanta.

  4. Edmonds LD, Layde PM, James LM, Flynt JW Jr, Erickson JD, Oakley GP Jr. Congenital malformations surveillance: two American systems. Int J Epidemiol 1981;10:247-52.

  5. Windham GC, Edmonds LD. Current trends in the incidence of neural tube defects. Pediatrics 1982;70:333-7.

  6. Adams MM, Erickson JD, Layde PM, Oakley GP. Down's syndrome: recent trends in the United States. JAMA 1981;246:758-60.

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