Racial/Ethnic Disparities in Neonatal Mortality --- United States, 1989--2001

Neonatal mortality (i.e., death at age <28 days) accounts for approximately two thirds of infant deaths in the United States. During 1989--2001, neonatal mortality rates (NMRs) declined; however, 2002 preliminary data indicated an increase. To characterize trends in neonatal mortality by gestational age and race/ethnicity, CDC analyzed linked birth/infant death data sets for 1989--1991 and 1995--2001 (2002 linked data were not available). This report summarizes the results of that analysis, which indicated that 1) extremely preterm infants (i.e., born at <28 weeks' gestation) accounted for 49%--58% of neonatal deaths during 1989--2001 and 2) racial/ethnic disparities persisted despite NMR declines among infants of all gestational ages. Public health practitioners, researchers, and clinicians can use these results to determine the efficacy of prevention programs at a national level and consider new studies and programs aimed at reducing preterm births and NMR disparities among racial/ethnic populations.

The number of neonatal deaths was obtained from linked birth/infant death data sets for 1989--1991 and 1995--2001 from CDC's National Center for Health Statistics (1). These data sets link birth- and death-certificate files for infants aged <1 year who died in the United States*.

NMRs (i.e., deaths at age <28 days per 1,000 live births) among births to U.S. residents were stratified by gestational age and maternal race/ethnicity. Period of gestation was measured on the birth certificate from the first day of the last normal menstrual period to the day of birth. Births with unknown gestational age or implausible birthweight/gestational age combinations (2) accounted for <3% of births annually and were excluded from the gestational age-specific analysis. Births at <37 weeks' gestation were classified as preterm and further classified into <28, 28--31, and 32--36 weeks' gestation. Ethnicity was based on the mother's origin as Hispanic or non-Hispanic. For this report, whites, blacks, American Indians/Alaska Natives (AI/ANs), and Asians/Pacific Islanders (A/PIs) are all non-Hispanic. Log-linear--weighted least squares regression was used to estimate the average annual percentage change in mortality during 1989--2001 for gestational age and race/ethnicity.

During 1989--2001, neonatal mortality in the United States declined 25%, from 6.0 deaths per 1,000 live births to 4.5. In 1989 and 2001, NMRs were highest for blacks (11.5 and 8.9, respectively) and lowest for A/PIs (4.3 and 3.1, respectively) (Table 1). In 2001, the NMR for AI/ANs was 4.1; whites, 3.8; and Hispanics, 3.6. Average annual percentage decline in NMRs during 1989--2001 ranged from 1.9% (A/PIs) to 3.0% (AI/ANs).

In 1989 and 2001, preterm infants accounted for approximately 70% of all neonatal deaths. In 2001, preterm infants accounted for 84% of black neonatal deaths and 72%--75% of deaths among infants of other races/ethnicities. Extremely preterm infants accounted for 49% of neonatal deaths overall in 1989 and 58% in 2001. In addition, in 2001, extremely preterm infants accounted for 50%--54% of neonatal deaths among all racial/ethnic populations, except blacks, for whom they comprised 70% of neonatal deaths.

Among extremely preterm infants, NMRs were highest for AI/ANs in 1989 and whites in 2001 (Table 2). Among infants born at 28--31 weeks' gestation, NMRs were highest for whites. NMRs for whites also were highest among infants born at 32--36 weeks' gestation in 1989 but were second to NMRs for AI/ANs in 2001 (Table 2). During 1989--2001, the average annual percentage decline in NMRs among preterm gestational age groups in all racial/ethnic categories was lowest for infants born at <28 weeks' gestation (0.9%--2.5%), compared with infants born at 28--31 and 32--36 weeks' gestation (3.1%--6.4% and 2.3%--4.5%, respectively). Among each preterm group, average annual percentage declines in mortality were lower for blacks and A/PIs. Preterm white infants had greater percentage declines in mortality during this period; however, they continued to have higher NMRs compared with preterm infants of other races/ethnicities (Table 2).

In 1989 and 2001, NMRs among infants born at >37 weeks' gestation were highest among blacks and AI/ANs (Table 2). Average annual percentage declines were highest among AI/ANs (5.6%) and A/PIs (5.3%) and lowest for whites (3.0%). In 2001, NMRs within all racial/ethnic populations ranged from 0.7 to 1.2 (Table 2).

Reported by: SL Lukacs, DO, KC Schoendorf, MD, Office of Analysis and Epidemiology, National Center for Health Statistics, CDC.

Editorial Note:

The findings in this report document a considerable decline in neonatal mortality among infants of all gestational ages and racial/ethnic populations during the 1990s; despite this decline, racial/ethnic disparities persisted. Implementation of new therapies and recommendations likely contributed to the decline; however, the effects of these advances might differ within racial/ethnic populations. The medical advances include 1) surfactant therapy, which improves infant lung maturity, resulting in a decreased risk for death for high-risk preterm infants (3); 2) folic acid consumption by women of childbearing age to reduce the risk for neural tube defects (4); and 3) intrapartum antimicrobial prophylaxis for women colonized with or at high risk for maternal-infant transmission of group B streptococcal infection (5,6).

In 2001, blacks continued to have the highest overall NMR, more than twice that of any other racial/ethnic population. The high rate among this population is likely attributable to a combination of high mortality among black infants born at >37 weeks' gestation (full-term infants account for approximately 90% of all births) and a high proportion of preterm births (17.6% black preterm births versus 10.8% white preterm births) (7).

Preterm white infants had higher NMRs in 2001, compared with other racial/ethnic populations, despite a greater rate of decline in mortality. Although black preterm infants had lower NMRs in 2001, the annual rate of decline was lower than among other racial/ethnic populations. The narrowing gap in mortality between preterm white infants and preterm black infants might reflect the widened distribution of neonatal intensive care in the 1990s beyond urban tertiary-care centers and a possible difference in benefit from surfactant therapy between black and white infants (8).

Differences in neonatal mortality trends among racial/ethnic populations also might be explained by changing patterns in the occurrence of multiple births (9). The rate of multiple births has increased substantially over the preceding decade, and trends vary among infants of different races/ethnicities. Further analysis examining these differences is needed.

The findings in the report are subject to at least four limitations. First, although greater declines in mortality were found among AI/ANs, the number of infants in this population is small, and trends should be interpreted with caution. Second, NMRs for AI/ANs might be underestimated because of underreporting of very low birthweight infants born on reservations (10). Third, gestational age reporting on birth certificate data might be misclassified; however, exclusion of implausible birthweight/gestational age combinations reduces the impact of this limitation. Finally, NMRs during 1995--2001 might vary from reported U.S. vital statistics rates during 1995--2001, which used weighted data to adjust for unlinked infant deaths. To be consistent with data during 1989--1991, unweighted data were used for this trend analysis.

Approximately half of all neonatal mortality occurred in infants born at <28 weeks' gestation, and the percentage has increased over the preceding decade. This increasing trend deserves more detailed analysis and suggests that prevention of these extremely preterm births will contribute to reducing neonatal mortality in the future.

References

1. National Center for Health Statistics. National Center for Health Statistics linked birth/infant death data set: 1989--91 cohort data, 1995--2001 period data. Hyattsville, Maryland: U.S. Department of Health and Human Services, CDC, National Center for Health Statistics, 2003.
2. Alexander GR, Himes JH, Kaufman RB, Mor J, Kogan M. A United States national reference for fetal growth. Obstet Gynecol 1996;87:163--8.
3. Horbar JD, Wright EC, Onstad L, and the National Institute of Child Health and Human Development Neonatal Research Network. Decreasing mortality associated with the introduction of surfactant therapy: an observational study of neonates weighing 601 to 1,300 grams at birth. Pediatrics 1993;92:191--6.
4. CDC. Spina bifida and anencephaly prevalence---United States, 1991--2001. MMWR 2002;51(No. RR-13).
5. CDC. Prevention of perinatal group B streptococcal disease: a public health perspective. MMWR 1996;45(No. RR-7).
6. Schrag SJ, Zywicki S, Farley MM, et al. Group B streptococcal disease in the era of intrapartum antibiotic prophylaxis. N Engl J Med 2000;342:15--20.
7. Martin JA, Hamilton BE, Ventura SJ, Menacker F, Park MM, Sutton PD. Births: final data for 2001. Hyattsville, Maryland: U.S. Department of Health and Human Services, CDC, National Center for Health Statistics, 2002; Natl Vital Stat Rep 2002;51(2).
8. Hamvas A, Wise PH, Yang RK, et al. The influence of the wider use of surfactant therapy on neonatal mortality among blacks and whites. N Engl J Med 1996;334:1635--40.
9. Martin JA, Park MM. Trends in twin and triplet births: 1980--97. Hyattsville, Maryland: U.S. Department of Health and Human Services, CDC, National Center for Health Statistics, 1999; Natl Vital Stat Rep 1999;47(24).
10. Heck KE, Schoendorf KC, Parker J. Are very low birthweight births among American Indians and Alaska Natives underregistered? Int J Epidemiol 1999;28:1096--101.

* Data for 1992--1994 were not analyzed because no national files linked deaths to births for those years.

Table 1


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Table 2


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