Racial Differences by Gestational Age in Neonatal Deaths Attributable to Congenital Heart Defects --- United States, 2003--2006

Congenital heart defects are diagnosed in approximately 1% of births in the United States (1) and account for the largest proportion of infant mortality attributable to birth defects (2). Congenital heart defects are multifactorial in origin and have several recognized genetic causes (e.g., DiGeorge and Williams-Beuren syndromes) (3) and noninherited risk factors (e.g., maternal pregestational diabetes and rubella infection) (4). Approximately 70% of infant deaths attributable to congenital heart defects occur neonatally (age <28 days) (5). U.S. studies have shown that all-cause neonatal mortality rates are higher among term infants of black mothers compared with white mothers, but lower among preterm infants of black mothers compared with white mothers (6,7). To assess neonatal mortality attributable to congenital heart defects by maternal race and gestational age, CDC analyzed linked U.S. birth and infant death data for 2003--2006. This report summarizes the results of that analysis, which found that 4.2% of all neonatal deaths and 24.5% of neonatal deaths attributable to birth defects had a congenital heart defect noted as the underlying cause. Among preterm births (<37 completed weeks' gestation), neonatal mortality rates attributable to congenital heart defects were lower for blacks (4.5 per 10,000 live births) compared with whites (6.8). However, among term births (≥37 completed weeks' gestation), neonatal mortality rates attributable to congenital heart defects were higher for blacks (1.5 per 10,000 live births) than for whites (1.3). The reasons for these racial differences by gestational age are unclear and will require further examination, including assessment of differences in prenatal diagnosis and prevalence at birth of congenital heart defects, and reporting of causes of death.

This analysis used 2003--2006 linked* birth/infant death data, the most recent available.† Included were records of all neonates (aged <28 days) whose underlying cause of death on the death certificate was classified as a congenital heart defect according to the International Classification of Diseases, 10th Revision, with codes Q20.0--Q26.9 (excluding Q21.1, persistent foramen ovale§ and Q25.0, patent ductus arteriosus, because these are considered normal conditions of prematurity). The analysis was restricted to infants of white and black mothers as reported on the birth certificate; those of Hispanic ethnicity and other racial/ethnic groups were excluded. Linked records with a missing gestational age (0.6% of the total), those with implausible gestational ages based on Alexander's index of birth weight for gestational age norms (0.6%) (6), and those with gestational ages <20 weeks or >44 weeks (1.1%) were excluded.

Because not all infant death records could be linked to the corresponding birth certificate, estimates of neonatal deaths were weighted according to the percentage of records linked by state and age at death. Poisson regression was used to calculate the rate ratio (RR) comparing neonatal mortality attributable to congenital heart defects among infants of black mothers with white mothers by gestational age group. Congenital heart defect neonatal mortality rates by weeks of gestational age also were estimated for infants of black mothers compared with white mothers.

The analysis included 11,383,665 live births in the United States during 2003--2006. Overall, of 54,008 neonatal deaths, 2,256 (4.2%) had a congenital heart defect noted as the underlying cause, including 1,777 (5.4%) of 33,205 infants of white mothers and 479 (2.3%) of 20,803 infants of black mothers. Deaths attributable to congenital heart defects were 24.5% of all neonatal deaths attributable to birth defects. The neonatal mortality rate attributable to congenital heart defects was 2.0 per 10,000 live births (Table 1). Hypoplastic left heart syndrome was the most commonly specified congenital heart defect--related underlying cause of neonatal death for infants of white (480 [27%]) and black (126 [26%]) mothers; 38% of the deaths were listed as "congenital malformation of heart, unspecified" (Table 2). A significantly lower proportion of neonatal deaths with transposition of the great arteries as the underlying cause occurred in infants of black mothers (2%) compared with white mothers (6%), but a significantly higher proportion of neonatal deaths caused by pulmonary atresia occurred in infants of black mothers (3%) compared with white mothers (2%).

Preterm infants (born at <37 weeks' gestation) accounted for 18% of the 2,312,080 births to black mothers and 11% of the 9,071,585 births to white mothers (Table 1). Neonatal mortality rates attributable to congenital heart defects varied by week of gestation and maternal race (Figure). Overall, neonatal mortality rates attributable to congenital heart defects were not significantly different when comparing infants of black mothers (2.1 per 10,000 live births) with infants of white mothers (2.0) (Rate ratio [RR] = 1.1; p = 0.28) (Table 1). However, the neonatal mortality rate attributable to congenital heart defects among preterm infants of black mothers (4.5 per 10,000) was significantly lower than that for preterm infants of white mothers (6.8) (RR = 0.7; p<0.001). In contrast, among infants delivered at 37--44 weeks, the neonatal mortality rate attributable to congenital heart defects among infants of black mothers (1.5 per 10,000) was higher than the neonatal mortality rate among infants of white mothers (1.3) (RR = 1.2; p = 0.03).

Reported by

JR Petrini, PhD, Perinatal Data Center, March of Dimes National Office, Danbury Hospital, Danbury, Connecticut. CS Broussard, PhD, SM Gilboa, PhD, KA Lee, MS, M Oster, MD, MA Honein, PhD, Div of Birth Defects and Developmental Disabilities, National Center on Birth Defects and Developmental Disabilities, CDC.

Editorial Note

The findings in this report indicate that although the overall neonatal mortality rate from congenital heart defects does not differ significantly between infants born to white and black mothers, differences can be observed by gestational age group. Among term infants, the rate for neonatal mortality attributable to congenital heart defects was 20% higher among infants of black mothers compared with white mothers, but among preterm infants, the rate was 30% lower for infants of black mothers compared with white mothers. Similar patterns have been reported for all-cause neonatal mortality by gestational age group in the United States during 1989--2001 (7). Although reports of infant mortality attributable to any birth defect have indicated that infants born to black mothers had higher mortality rates than infants born to whites (2,5), these studies did not analyze the differences by gestational age.

The reason for the lower rate of all-cause neonatal mortality among preterm infants of black mothers compared with white mothers is unclear. One possibility is that live-born infants who die shortly after birth might be misclassified as fetal deaths, particularly those born at early gestational ages (7). The fetal mortality rate in the United States is approximately twice as high among blacks as among whites (8), and differences by race in reporting fetal deaths versus early neonatal deaths might exist. Recent research has shown variation by state in classification of neonatal death at <24 hours versus fetal death for infants at the limits of viability (i.e., gestation of <24 weeks or birth weight <500 g) (9). Whether such variation might also occur by race is unknown.

Also unclear is whether factors specific to congenital heart defects contribute to the differences in black and white neonatal mortality patterns by gestational age. Potentially, differences in prevalence of specific types of congenital heart defects might explain the differences in mortality patterns; however, previous studies examining congenital heart defect prevalence have not identified many racial differences in specific types of congenital heart defects or in congenital heart defects overall (1,10). Among studies that included birth defect prevalence among live births, stillbirths, and pregnancy terminations, no racial difference was observed for prevalence of hypoplastic left heart syndrome, the most common specific cause of death attributable to congenital heart defects (1,10). Some data have shown that infants of black mothers have a lower prevalence of transposition of the great arteries (1,10) and coartaction of the aorta (1), but a higher prevalence of tetralogy of Fallot (10) and pulmonary atresia/stenosis (1).

The findings in this report are subject to at least three limitations. First, because of the large percentage of cases in which the underlying cause of death was unspecified, the results related to the distribution of specific causes should be interpreted with caution. Second, this analysis only included deaths with a congenital heart defect listed as the underlying cause; deaths were not included if congenital heart defects were instead classified as a contributing cause (e.g., Down syndrome as underlying with atrioventricular septal defect as contributing). However, such possible underestimation of deaths attributable to congenital heart defects would impact the analysis of racial differences only if differential reporting of the underlying cause of death occurred among racial groups. Finally, gestational age can be inaccurate on the birth certificate and might be less accurate among preterm births (6). Although cases with implausible gestational age/birth weight combinations were excluded, this analysis might have included some misclassified gestational ages.

Adjusting for gestational age or its correlates (such as birth weight), as has been done in some previous studies, obscures the differences in neonatal mortality rates by gestational age, and thus should be avoided. Efforts to reduce neonatal mortality rates attributable to congenital heart defects should include strategies to decrease mortality among infants with congenital heart defects through timely and appropriate medical and surgical treatment and to prevent the occurrence of congenital heart defects, where possible, by addressing modifiable potential risk factors such as pregestational diabetes, obesity, and maternal smoking (4). The role of gestational age in differences in neonatal mortality among infants born to white and black mothers is unclear and requires further investigation, including assessment of differences in prenatal diagnosis, prevalence at birth of congenital heart defects, and reporting of causes of death.

Acknowledgments

This report is based, in part, on contributions by H Chen, Dept of Biostatistics, Harvard School of Public Health, Boston, Massachusetts; and Q Yang, Office of Public Health Genomics, A Correa, O Devine, National Center on Birth Defects and Developmental Disabilities, CDC.

References

1. Botto LD, Correa A, Erickson JD. Racial and temporal variations in the prevalence of heart defects. Pediatrics 2001;107:e32.
2. CDC. Trends in infant mortality attributable to birth defects---United States, 1980--1995. MMWR 1998;47:773--8.
3. Yang Q, Chen H, Correa A, Devine O, Mathews TJ, Honein MA. Racial differences in infant mortality attributable to birth defects in the United States, 1989--2002. Birth Defects Res A Clin Mol Teratol 2006;76:706--13.
4. Jenkins KJ, Correa A, Feinstein JA, et al. Noninherited risk factors and congenital cardiovascular defects: current knowledge. A scientific statement from the American Heart Association Council on Cardiovascular Disease in the Young, endorsed by the American Academy of Pediatrics. Circulation 2007;115:2995--3014.
5. Pierpont ME, Basson CT, Benson DW Jr, et al. Genetic basis for congenital heart defects: current knowledge. A scientific statement from the American Heart Association Congenital Cardiac Defects Committee, Council on Cardiovascular Disease in the Young, endorsed by the American Academy of Pediatrics. Circulation 2007;115:3015--38.
6. Alexander GR, Kogan M, Bader D, Carlo W, Allen M, Mor J. US birth weight/gestational age-specific neonatal mortality: 1995--1997 rates for whites, Hispanics, and blacks. Pediatrics 2003;111:e61--6.
7. CDC. Racial/ethnic disparities in neonatal mortality---United States, 1989--2001. MMWR 2004;53:655--8.
8. CDC. Racial/ethnic trends in fetal mortality---United States, 1990--2000. MMWR 2004;53:529--32.
9. Ehrenthal DB, Wingate MS, Kirby RS. Variation by state in outcomes classification for deliveries less than 500 g in the United States. Matern Child Health J 2010;January 29:epub ahead of print.
10. Canfield MA, Honein MA, Yuskiv N, et al. National estimates and race/ethnic-specific variation of selected birth defects in the United States, 1999--2001. Birth Defects Res A Clin Mol Teratol 2006;76:747--56.

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