Leading Major Congenital Malformations Among Minority Groups in the United States, 1981-1986

Gilberto F. Chavez, M.D., M.P.H. Jose F. Cordero, M.D., M.P.H. Jose E. Becerra, M.D., M.P.H. Birth Defects and Genetic Diseases Branch Division of Birth Defects and Developmental Disabilities Center for Environmental Health and Injury Control

INTRODUCTION

Congenital malformations are a major cause of infant morbidity and mortality in the United States (1). In 1985, birth defects were the leading cause of infant mortality (2) and the fifth leading cause of years of potential life lost (3). Birth defects contribute significantly to chronic disease morbidity and related medical costs. Approximately 30% of all admissions to pediatric hospitals are associated with birth defects, and expenditures for medical care have been estimated at $1.4 billion per year (4).

All populations share the burden of congenital malformations, although the frequency and types of malformations may vary by race, ethnicity, and socioeconomic status (5-11). Access to medical care, nutrition, maternal lifestyles, and education are considered to be important factors in the occurrence of neural tube defects (5). Erickson (6) reported that in Atlanta, Georgia, the incidence of several common birth defects varies substantially between blacks and whites.

A large prospective study showed that blacks had higher overall rates of malformations than whites; this difference was primarily due to an increase in minor malformations such as polydactyly, branchial clefts, and supernumerary nipples, whereas whites had higher rates of major malformations and multiple malformations (7). Higher rates of neural tube defects were observed among infants of Hispanic women born in Puerto Rico and residing in Brooklyn than in their non-Hispanic black and white counterparts (8). American Indians appear to be at high risk for fetal alcohol syndrome. According to a recent study, the fetal alcohol syndrome rates for American Indians of the southwestern United States range from 13 to 103 per 10,000 live births (9). These rates vary greatly by subpopulation group (tribe). Several factors, such as culture influences, fertility, patterns of alcohol consumption, nutrition, and metabolic differences, are believed to play an important role in the distribution and occurrence of fetal alcohol syndrome among American Indians (10). Furthermore, oral clefts and congenital heart anomalies reportedly occur more frequently among American Indians in British Columbia than in the general population (11).

In 1981, CDC, through the Birth Defects Monitoring Program (BDMP) of the Birth Defects and Genetic Diseases Branch, Division of Birth Defects and Developmental Disabilities, Center for Environmental Health and Injury Control, began collecting data on the race and ethnicity of malformed infants born in the United States. This report summarizes available BDMP data on the leading major congenital malformations among blacks, Hispanics, American Indians*, and Asians in the United States during the period 1981-1986 and compares the prevalence rates for these groups with those for whites. MATERIALS AND METHODS

The primary objective of the BDMP, which was established at CDC in December 1974, is to serve as an early warning system for detecting changes or unusual trends in the rates of congenital anomalies in the United States. A secondary objective is to correlate occurrence patterns of birth defects with geographic and temporal trends in the distribution of possible human teratogens (12). The BDMP monitors 161 diagnoses, including structural, chromosomal, biochemical, and genetic disorders. BDMP data are obtained through the Commission on Professional and Hospital Activities (CPHA). The Commission's Professional Activities Study (PAS) system collects data from approximately 1,500 U.S. hospitals with obstetrics services. At each hospital, staff members of the medical records department review the chart of each newborn or stillborn delivered, prepare a case abstract, and send it to CPHA for processing. CPHA then sends portions of these abstracts to CDC for inclusion in the BDMP. Information provided to CDC includes the state, county, and hospital where the birth occurred; medical record number; zip code of maternal residence; birth date; birth status; gender; discharge status; and up to 15 diagnoses and 15 procedures coded according to the International Classification of Diseases, Ninth Revision. These data represent the largest source of information available on malformed infants born in the United States.

In 1981, the racial/ethnic variable was changed from "white or other" to more specific categories. The racial/ethnic classification now includes six categories: white, black, Hispanic, American Indian, Asian, and other. The infant's racial/ethnic classification is derived from the information recorded in the medical record. Children of mixed race/ethnicity are coded as "other." In addition, children of uncertain heritage are coded as "unknown."

During 1981-1986, approximately 1,236 PAS hospitals voluntarily participated in BDMP. The majority (69.2%) of these hospitals reported fewer than 1,000 births per year. The BDMP, through PAS, covered an average of 21.1% of all U.S. annual births.

In the period 1981-1986, the BDMP monitored 4,617,613 births. Information on specific race and ethnicity was available for 92.6% of these births. The BDMP coverage of the total number of births in the United States for each racial/ethnic group was as follows: 19.7% for whites, 16.4% for blacks, 17.5% for Hispanics, 9.3% for American Indians, and 8.3% for Asians. Rates of the 15 leading major congenital malformations for each racial/ethnic group were computed and simultaneously compared with those of the other groups (18 malformations overall) to determine which group had the highest rate. For each group, the total number of cases of each malformation was used as the numerator, and the total number of births reported through BDMP was used as the denominator. Later, rates of the 15 leading major malformations for each group were compared with the rates for whites in the BDMP for the same period. The rate ratio and its 95% confidence interval (CI) were computed. Statistical significance was established if the CI did not include one (pless than 0.05). RESULTS

An analysis of the 18 major birth defects by racial/ethnic group showed that American Indians had the highest total rate, followed by whites, blacks, Asians, and Hispanics, respectively (Table 1). American Indians had the highest rates of hydrocephalus without spina bifida; atrial septal defect; valve stenosis and atresia; cleft palate without cleft lip; cleft lip with or without cleft palate; rectal atresia and stenosis; fetal alcohol syndrome; and autosomal abnormalities, excluding Down syndrome. Rates for clubfoot without central nervous system (CNS) defects, hip dislocation without CNS defects, and hypospadias were highest among whites. Rates for microcephalus, patent ductus arteriosus, and pulmonary artery stenosis were highest among blacks. The highest rates of anencephaly, spina bifida without anencephaly, and Down syndrome occurred among Hispanics. The rates for two major birth defects--anencephaly and ventricular septal defect--were highest among Asians.

Among blacks, rates for six malformations were statistically significantly higher and rates for nine malformations were statistically significantly lower than rates among whites (Table 2). Patent ductus arteriosus was the leading major congenital anomaly among blacks, possibly reflecting the high rate of prematurity in blacks (3). Patent ductus arteriosus occurred twice as frequently as hypospadias, the second leading major malformation among blacks. The fetal alcohol syndrome black:white rate ratio of 6.67 (CI = 5.71-7.79) was noteworthy.

Among Hispanics, the rates of anencephaly, microcephalus, and Down syndrome were significantly higher than those among whites (Table 3). Spina bifida without anencephaly was more prevalent among Hispanics, although the difference in rates was not statistically significant. Neural tube defects have been previously documented as being more prevalent among certain Hispanic subpopulations (8). The high rates of Down syndrome may be partially explained by advanced maternal age, inadequate access to medical care, or poor use of health services among Hispanics (9). On the other hand, rates for seven major congenital malformations were statistically significantly lower for Hispanics than for whites.

As among blacks, patent ductus arteriosus was the most prevalent congenital malformation among American Indians; it was followed by hip dislocation without CNS defects and fetal alcohol syndrome (Table 4). The rate of fetal alcohol syndrome among American Indians was 29.9 per 10,000 total births, and the rate ratio was 33.22 (CI = 25.08-44.00) compared with whites. Rates for other malformations were also statistically significantly higher for American Indians than for whites; these malformations were valve stenosis and atresia, hydrocephalus without spina bifida, cleft lip with or without cleft palate, and cleft palate without cleft lip. Rates for hypospadias and clubfoot without CNS defects were statistically significantly lower for American Indians than for whites.

Most prevalent among Asians were patent ductus arteriosus and hip dislocation without CNS defects. Rates for anencephaly, Down syndrome, cleft lip with or without cleft palate, and ventricular septal defect tended to be statistically significantly higher among Asians than among whites. Rates for hip dislocation without CNS defects, hypospadias, and clubfoot without CNS defects were statistically significantly lower among Asians than among whites (Table 5).

DISCUSSION

The overall distribution of the leading major congenital malformations among blacks, Hispanics, American Indians, and Asians in the United States has not been previously documented. Results of several studies (5-11) have suggested that the rates of some malformations vary by socioeconomic status, race, and ethnicity. This report provides the first estimates of the 15 leading major congenital malformations among four minority groups in the United States and identifies groups at higher risk for some congenital anomalies. Furthermore, it provides baseline rates that should prove useful in identifying trends and clusters of malformations among minority groups.

The BDMP data provided in this report show that the frequency and the types of malformations vary greatly among minority groups in the United States. Certain racial/ethnic groups have a greater burden of some malformations than others. For blacks, the prevalence of patent ductus arteriosus is substantially higher than that for any other group studied, and the rate of fetal alcohol syndrome is more than six times that for whites. The rates of neural tube defects and Down syndrome are significantly higher among Hispanics. American Indians have a 33-fold higher rate of fetal alcohol syndrome than whites, and they also have statistically significantly higher rates of oral clefts and most cardiovascular defects. The rate of anencephaly among Asians parallels that among Hispanics and is significantly higher than the rates among other groups. In addition, Asians have higher rates of Down syndrome, cleft lip with or without cleft palate, and ventricular septal defect.

Although minor birth defects were not included in this report because they are not a significant cause of morbidity and mortality, BDMP data showed that rates of polydactyly, breast anomalies (mostly supernumerary nipples), branchial clefts, and anomalies of the abdominal wall (mostly umbilical hernias) are highest among blacks.

The data in this report must be interpreted with caution. Some of the overall differences in the distribution of malformations among different racial/ethnic groups may be explained as follows:

1. In some instances, physicians may tend to look for a particular malformation more in certain racial/ethnic groups than they would in others (detection bias). For example, some hospitals mainly serve minority groups believed to be at higher risk for some malformations. 2) Since BDMP data are not obtained from a random sample of U.S. hospitals, some of the participating hospitals may have a higher or lower than usual proportion of high-risk pregnancies and births. 3) Rates of congenital anomalies may be different in BDMP hospitals than in other hospitals because of their size or affiliation (public versus private). Nevertheless, hospitals that reported to BDMP in the study period ranged from those having fewer than 200 births to those having more than 1,000 births per year. The hospitals were located throughout the United States, and both privately owned and publicly owned hospitals were included. 4) Socioeconomic factors, such as education, access to medical care, nutrition, maternal lifestyles, and cultural influences, cannot be ruled out as major contributors to the burden of some malformations among certain minority groups. 5) Many of these major congenital malformations may have been associated with genetic and environmental factors. 6) The heterogeneity within minority groups is not addressed in this report. Some racial/ethnic subgroups (for example, certain American Indian tribes; Mexican-American, Cuban, or Puerto Rican Hispanics; and Japanese, Chinese, or other Asians) may account for a larger share of the group's total rate of some malformations.

In conclusion, the importance of monitoring congenital malformations by race and ethnicity has been demonstrated, and notable differences in the overall distribution of these anomalies have been identified. Much work remains to be done in the fight against the number one cause of infant mortality, and public health professionals need to address the problem of why certain minority groups have a higher risk for some congenital malformations than other segments of the population.

References

1. Oakley GP Jr. Frequency of human congenital malformations. Clin Perinatol 1986;13:545-54.

2. National Center for Health Statistics. Advance report of final mortality statistics, 1985. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, 1987; DHHS publication no. (PHS)87-1120. (Monthly vital statistics report vol 36, no. 5, suppl.)

3. Centers for Disease Control. Table V. Estimated years of potential life lost before age 65 and cause-specific mortality, by cause of death--United States, 1985. MMWR 1987;36:313.

4. Flynt JW, Norris CK, Zaro S, Kitchen SB, Kotler M, Ziegler

1. State surveillance of birth defects and other adverse reproductive outcomes. Final report. George Washington University: Macro Systems, Inc, April 1987.

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

6. Erickson JD. Racial variations in the incidence of congenital malformations. Ann Hum Genet 1976;39:315-20.

7. Myrianthopoulos NC. Racial differences. In: Malformations in children from one to seven years: a report from the Collaborative Perinatal Project. New York: Alan R Liss, Inc, 1985:55-64.

8. Feldman JG, Stein SC, Klein RJ, Kohl S, Casey G. The prevalence of neural tube defects among ethnic groups in Brooklyn, New York. J Chronic Dis 1982;35:53-60.

9. US Department of Health and Human Services. Report of the Secretary's Task Force on Black and Minority Health. Washington, DC: US Department of Health and Human Services, 1985.

10. Aase JM. The fetal alcohol syndrome in American Indians: a high risk group. Neurobehav Toxicol Teratol 1981;3:153-6.

11. Lowry RB, Thunem NY, Silver M. Congenital anomalies in American Indians of British Columbia. Genet Epidemiol 1986;3:455-67.

12. Edmonds LD, Layde PM, James LM, Flynt JW, Erickson JD, Oakley GP Jr. Congenital malformations surveillance: two American systems. Int J Epidemiol 1981;10:247-52. *Throughout this report, the term "American Indians" includes Alaskan Natives.

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