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Infant Deaths — United States, 2005–2008

Marian F. MacDorman, PhD, T. J. Mathews, MS

National Center for Health Statistics, CDC


Corresponding author: Marian F. MacDorman, PhD, Division of Vital Statistics, National Center for Health Statistics, CDC. Telephone: 301-458-4356; E-mail: mfm1@cdc.gov.

Introduction

Infant mortality rates are associated with maternal health, quality of and access to medical care, socioeconomic conditions, and public health practices, which makes infant mortality an increasingly important public health concern (1,2). After large declines throughout the twentieth century, the U.S. infant mortality rate did not decline significantly during 2000–2005 (3). Analysis of 2000–2004 infant mortality in the United States indicated considerable disparities by race and Hispanic origin (4). Race and ethnic disparities in U.S. infant mortality have been apparent since vital statistics data began to be collected more than 100 years ago. These disparities have persisted over time, and research indicates that not all groups have benefited equally from social and medical advances (5–7).

The infant mortality analysis and discussion that follows is part of the second CDC Health Disparities and Inequalities Report (CHDIR) (4). The 2011 CHDIR (8) was the first CDC report to assess disparities across a wide range of diseases, behavioral risk factors, environmental exposures, social determinants, and health-care access. The criteria for inclusion of topics that are presented in the 2013 CHDIR are based on criteria that are described in the 2013 CHDIR Introduction (9). This report provides more current information on infant mortality rates on the basis of race/ethnicity, mother's place of birth, and by state and region. The purposes of this infant mortality analysis are to raise awareness of differences in infant mortality by selected maternal and infant characteristics, and to prompt actions to reduce these disparities.

Methods

To estimate disparities in infant mortality rate by selected characteristics and specified group, CDC analyzed data from the United States linked birth/infant death data sets (linked files) for 2005 through 2008 (the latest year for which accurate race/ethnicity data are available) (5). In these data sets, information from the birth certificate is linked to information from the death certificate for each infant (aged <1 year) who dies in the United States. Characteristics analyzed included sex, maternal race/ethnicity, maternal place of birth, and the state of residence of the mother at the time of birth. Household income and educational attainment were not analyzed because they were either not collected or not collected consistently on birth certificates. Maternal race was defined as white, black, Asian/Pacific Islander, and American Indian/Alaska native. Ethnicity is defined as Hispanic or non-Hispanic. Hispanic data were further subdivided into Mexican, Puerto Rican, Cuban, and Central and South American. Place of birth was defined as born in the 50 states and DC, or born outside of the 50 states and DC.

Infant mortality rates were calculated as the number of infant deaths per 1,000 live births in the specified group (i.e., by maternal race/Hispanic origin, maternal birthplace, state of residence, and infant gender). Ratios of non-Hispanic black to non-Hispanic white infant mortality rates were computed to assess the magnitude of the disparity in non-Hispanic black and non-Hispanic white infant mortality rates by state. Data from 2006–2008 were aggregated to obtain statistically reliable state-specific rates by race and Hispanic origin; rates are not shown for cells with <20 infant deaths. Rates based on <20 infant deaths are not shown separately as they do not meet standards of reliability or precision. Differences between infant mortality rates were assessed for statistical significance by using the z test (p<0.05).

Disparities were measured as the deviations from a "referent" category rate. Absolute difference was measured as the simple difference between a population subgroup mortality rate and the rate for its respective reference group. The relative difference, a percentage, was calculated by dividing the difference by the value in the referent category and multiplying by 100.

Results

The U.S. infant mortality rate declined 10% from 2005 to 2010, from 6.86 infant deaths per 1,000 live births in 2005 to a preliminary estimate of 6.14 in 2010 (5,13). In 2008, the overall U.S. infant mortality rate was 6.61 infant deaths per 1,000 live births, with differences by race and Hispanic origin (Table 1). The highest infant mortality rate was for non-Hispanic black women (12.67), with a rate 2.3 times that for non-Hispanic white women (5.52) (Table 1). Compared with non-Hispanic white women, infant mortality rates were 53% higher for American Indian/Alaska Native* women (8.42) and 32% higher for Puerto Rican women (7.29). Infant mortality rates for Asian/Pacific Islanders* (4.51) and Central or South American women (4.76) were lower than those for non-Hispanic white women. From 2005 to 2008, infant mortality rates declined approximately 4% for the total population and for non-Hispanic white women, approximately 7% for non-Hispanic black women, and 12% for Puerto Rican women; changes for other racial/ethnic groups were not statistically significant. When examined by place of birth of the mother, the 2008 infant mortality rate was 38% higher for women born in the 50 states and DC than for women born elsewhere (Table 1). The infant mortality rate was 21% higher for male than for female infants.

Differences also exist in infant mortality rates between various states, with a twofold or greater difference in rates between the states with the highest and lowest rates for the total population and for each race/ethnic group studied. Across the United States, infant mortality rates are generally higher in the South and Midwest and lower in other parts of the country. During 2006–2008, total infant mortality rates ranged from a high of 11.97 per 1,000 live births for DC and Mississippi 10.16 to a low of 4.94 for Massachusetts and Utah. However, because DC has high concentrations of high-risk women, its rate is more appropriately compared with rates for other large U.S. cities. For non-Hispanic white women, Alabama had the highest rate (7.67) and New Jersey the lowest rate (3.78). For non-Hispanic black women, the rate was highest in Hawaii (18.54) and lowest in Washington (7.66). For Hispanic women, the rate was highest in Pennsylvania (7.94) and lowest in Louisiana (3.92).

Ratios of non-Hispanic black to non-Hispanic white infant mortality rates were computed to assess the magnitude of the disparity in non-Hispanic black and non-Hispanic white infant mortality rates by state (Figure). Although the average rate ratio in the United States was 2.35, seven areas (Connecticut, DC, Hawaii, Massachusetts, New Jersey, New York, and Wisconsin) had rate ratios of 2.60 or greater. In contrast, seven other states (Arkansas, Alabama, Kentucky, Mississippi, Oklahoma, Oregon, and Washington) had ratios <2.10. Rate ratios are not shown for states with <20 non-Hispanic black infant deaths.

Discussion

The U.S. infant mortality rate has declined 10% from 2005 (6.86) to 2010 (preliminary estimate: 6.14) (5,13); however, disparities have persisted. Higher infant mortality rates for male than for female infants have persisted for many years and occur among most world populations, and have been explained in part by differences in genetic susceptibility to disease (14). Differences in infant mortality rates by race/ethnicity, maternal birthplace, and geographic area might reflect in part different population profiles, with regard to sociodemographic and behavioral risk factors. For example, infant mortality rates are higher than the U.S. average for adolescents, women aged ≥35 years, unmarried mothers, smokers, those with lower educational levels, or inadequate prenatal care (5). Substantial differences between groups in income and access to health care also might contribute to differences in infant mortality (15). Population groups with the lowest infant mortality rates tended to have a smaller percentage of births to women with some or all of these characteristics, whereas groups with the highest infant mortality rates tended to have a higher percentage of births in women with some or all of these characteristics. Other factors that might contribute to racial/ethnic differences in infant mortality include differences in maternal preconception health, infection, stress, racism, and social and cultural differences (7,16–21). However, the influence of an individual risk factor can vary considerably between population groups, indicating different medical profiles and life experiences for women of different backgrounds (7,16,21–22).

The risk factors for infant mortality discussed earlier (e.g., maternal age, tobacco use, lower income or educational levels, and inadequate prenatal care) are very similar to the risk factors for preterm or low birthweight delivery, and these risk factors can affect infant mortality either directly or through the mechanism of preterm or low birthweight delivery. In 2008, the percentage of infants born preterm (<37 completed weeks' gestation) was higher for non-Hispanic black (17.5%), Puerto Rican (14.1%), and American Indian/Alaska Native (13.6%) mothers, than for non-Hispanic white mothers (11.1%) (5). Infant mortality rates are substantially higher for preterm and low birthweight infants, and even limited changes in the percentages of preterm or low birthweight births can have a major impact on infant mortality (5,6). In fact, the recent decline in U.S. infant mortality is linked to a recent decline in the percentage of preterm births, from a high of 12.8% in 2006 to 12.0% in 2010 (5,22). Still the U.S. infant mortality rate was higher than for the majority of other developed countries, in part because of a substantially higher percentage of preterm births, a critical risk factor for infant mortality (23–24).

Limitation

The findings in this report are subject to at least one limitation. Differences in infant mortality rates for smaller states and certain race/ethnic groups (e.g., American Indians/Alaska Natives, Asians/Pacific Islanders, and Cubans) should be interpreted with caution, as small numbers of infant deaths (i.e., <20) in specific subcategories might lead to a lack of statistical precision.

Conclusion

Infant mortality remains a complex and multifactorial problem that will continue to challenge researchers and policymakers in the years ahead. Despite recent declines in the overall infant mortality rate, the longstanding disparities in infant mortality by racial/ethnic group, mother's birthplace, and geographic area persist. One of the Healthy People 2020 objectives is to achieve an infant mortality rate of 6.0 for the total population and for each race/ethnic group. Although the U.S. infant mortality rate of 6.14 in 2010 approximates the Healthy People 2020 objective, rates for several racial/ethnic groups are substantially higher than the goal (25). Prevention of preterm birth is critical to both lowering the overall infant mortality rate and to reducing racial/ethnic disparities (5,6).

References

  1. CDC. Achievements in public health, 1900–1999: healthier mothers and babies. MMWR 1999;48:849–58.
  2. Guyer B, Freedman MA, Strobino DM, Sondik EJ. Annual summary of vital statistics: trends in the health of Americans during the 20th century. Pediatrics 2000;106:1307–17.
  3. MacDorman MF, Mathews TJ. Recent trends in infant mortality in the United States. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; 2008. NCHS Data Brief no. 9. Available at http://www.cdc.gov/nchs/data/databriefs/db09.pdf.
  4. CDC. Infant deaths—United States, 2000–2007. In: CDC health disparities and inequalities report—United States, 2011. MMWR 2011;60(Suppl; January 14, 2011).
  5. Mathews TJ, MacDorman MF. Infant mortality statistics from the 2008 period linked birth/infant death data set. National Vital Statistics Reports vol 60 no 5. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; 2012.
  6. MacDorman MF, Mathews TJ. Understanding racial and ethnic disparities in US infant mortality rates. NCHS data brief, No. 74. Hyattsville, MD: National Center for Health Statistics. 2011. Available at http://www.cdc.gov/nchs/data/databriefs/db74.pdf.
  7. Krieger N, Rehkopf DH, Chen JT, et al. The fall and rise of US inequities in premature mortality: 1960–2002. PLoS Med 2008;5:e46.
  8. CDC. CDC health disparities and inequalities report—United States, 2011. MMWR 2011; 60(Suppl; January 14, 2011).
  9. CDC. Introduction. In: CDC health disparities and inequalities report—United States, 2013. MMWR 2013;62(No. Suppl 3).
  10. CDC. Period linked birth-infant death public-use data files [Downloadable data files]. Hyattsville, MD: US Department of Health and Human Services; 2012. Available at http://www.cdc.gov/nchs/data_access/VitalStatsOnline.htm.
  11. CDC. User's guide for the 2008 period linked birth/infant death data set. 2012. Available at http://www.cdc.gov/nchs/data_access/VitalStatsOnline.htm.
  12. Rosenberg HM, Maurer JD, Sorlie PD, et al. Quality of death rates by race and Hispanic origin: a summary of current research, 1999. Vital Health Stat 2 1999:1–13.
  13. Murphy SL, Xu J, Kochanek KD. Deaths: preliminary data for 2010. In: National Vital Statistics Reports. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics. NCHS Data Brief no 4; 2012. Available at http://www.cdc.gov/nchs/data/nvsr/nvsr60/nvsr60_04.pdf.
  14. Pongou R. Why is infant mortality higher in boys than in girls? A new hypothesis based on preconception environment and evidence from a large sample of twins. Demography [Epub ahead of print].
  15. DeNavas-Walt C, Proctor BD, Smith JC. Income, poverty, and health insurance coverage in the United States: 2010. Washington, DC: US Census Bureau; 2011. Current Population Reports no. P60–239. Available at http://www.census.gov/prod/2011pubs/p60-239.pdf.
  16. Geronimus AT. Black/white differences in the relationship of maternal age to birthweight: a population-based test of the weathering hypothesis. Soc Sci Med 1996;42:589–97.
  17. Fiscella K. Racial disparity in infant and maternal mortality: confluence of infection, and microvascular dysfunction. Matern Child Health J 2004;8:45–54.
  18. Hogan VK, Njoroge T, Durant TM, Ferre CD. Eliminating disparities in perinatal outcomes: lessons learned. Matern Child Health J 2001;5:135–40.
  19. Collins JW Jr, David RJ, Handler A, Wall S, Andes S. Very low birthweight in African American infants: the role of maternal exposure to interpersonal racial discrimination. Am J Public Health 2004;94:2132–8.
  20. Martin JA, Hamilton BE, Sutton PD, et al. Births: final data for 2008. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; 2010. National Vital Statistics Reports Vol. 59, no. 1. Available at http://www.cdc.gov/nchs/data/nvsr/nvsr59/nvsr59_01.pdf.
  21. Hummer RA, Powers DA, Pullum SG, Gossman GL, Frisbie WP. Paradox found (again): infant mortality among the Mexican-origin population in the United States. Demography 2007;44:441–57.
  22. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2010. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; National Vital Statistics Report vol 60 no 2. Available at http://www.cdc.gov/nchs/data/nvsr/nvsr60/nvsr60_02.pdf.
  23. MacDorman MF, Mathews TJ. Behind international rankings of infant mortality: how the United States compares with Europe. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; 2009. NCHS Data Brief no 23. Available at http://www.cdc.gov/nchs/data/databriefs/db23.htm.
  24. Organization for Economic Cooperation and Development. OECD Health Data 2013. Available at http://www.oecd.org/health/health-systems/oecdhealthdata.htm.
  25. CDC. HealthyPeople.gov; 2020 topics and objectives—maternal, infant and child health. Available at http://www.healthypeople.gov/2020/topicsobjectives2020/objectiveslist.aspx?topicId=26.

* Includes Hispanic and non-Hispanic women.


TABLE 1. Infant mortality rates* by selected characteristics — United States, 2005 and 2008

Characteristic

2005

2008

Infant
mortality
rate

Absolute
difference
(rate)

Relative
difference
(%)

Infant
mortality
rate

Absolute
difference
(rate)

Relative
difference
(%)

Total

6.86

6.61

Sex

Male

7.56

1.4

23.5

7.22

1.3

20.9

Female

6.12

Ref.

Ref.

5.97

Ref.

Ref.

Race/Ethnicity

White, non-Hispanic

5.76

Ref.

Ref.

5.52

Ref.

Ref.

Black, non-Hispanic

13.63

7.9

136.6

12.67

7.2

129.5

Asian/Pacific Islander§

4.89

-0.9

-15.1

4.51

-1.0

-18.3

American Indian/Alaska Native

8.06

2.3

39.9

8.42

2.9

52.5

Hispanic

5.62

-0.1

-2.4

5.59

0.1

1.3

Mexican

5.53

-0.2

-4.0

5.58

0.1

1.1

Puerto Rican

8.30

2.5

44.1

7.29

1.8

32.1

Cuban

4.42

-1.3

-23.3

4.90

-0.6

-11.2

Central and South American

4.68

-1.1

-18.8

4.76

-0.8

-13.8

Place of birth

Born in the 50 states and DC

7.26

2.2

42.9

6.99

1.9

38.4

Born outside the 50 states and DC

5.08

Ref.

Ref.

5.05

Ref.

Ref.

Abbreviation: Ref. = Referent.

Source: CDC. Period linked birth/infant death public-use data files (Downloadable data files). Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics. Available at http://www.cdc.gov/nchs/data_access/VitalStatsOnline.htm.

* Infant mortality rate = number of deaths among infants aged <1 year per 1,000 live births in a specific group.

Race and Hispanic origin are reported separately on birth certificates. Race categories are consistent with the 1977 Office of Management and Budget standards.Thirty states reported multiple-race data on the birth certificate in 2008. For the <2% of events in these states that reported multiple race data, the multiple-race data were bridged to the single race categories of the 1977 standards for compatibility with other states.

§ Includes persons of Hispanic or non-Hispanic origin.

Persons of Hispanic ethnicity might be of any race or combination of races.


TABLE 2. Infant mortality rates,* by race and Hispanic origin of mother and by state — United States, 2006–2008

Total

White,
non-Hispanic

Black,
non-Hispanic

Hispanic

United States

6.68

5.58

13.11

5.50

Alabama

9.47

7.67

13.73

7.50

Alaska

6.54

4.10

Arizona

6.54

6.04

14.85

6.13

Arkansas

7.89

6.70

13.53

5.71

California

5.12

4.51

10.72

4.88

Colorado

6.04

5.13

11.97

6.96

Connecticut

6.27

4.80

13.11

6.35

Delaware

8.03

5.89

13.46

7.10

District of Columbia

11.97

4.46

17.68

Florida

7.21

5.71

12.83

5.38

Georgia

8.02

5.87

12.70

5.06

Hawaii

6.04

4.58

18.54

4.98

Idaho

6.46

5.95

7.91

Illinois

7.10

5.70

13.45

5.91

Indiana

7.44

6.47

15.36

6.28

Iowa

5.43

5.06

11.10

6.61

Kansas

7.50

6.94

14.62

7.15

Kentucky

7.04

6.62

12.13

5.07

Louisiana

9.38

6.62

13.88

3.92

Maine

6.04

5.90

Maryland

7.98

5.50

12.98

5.33

Massachusetts

4.94

4.04

10.90

6.08

Michigan

7.56

5.87

14.70

7.09

Minnesota

5.55

4.77

11.33

4.64

Mississippi

10.16

7.07

13.82

6.64

Missouri

7.34

6.18

14.49

5.12

Montana

6.47

5.89

Nebraska

5.93

5.33

12.98

5.21

Nevada

6.10

5.29

12.54

5.69

New Hampshire

5.10

5.00

New Jersey

5.35

3.78

12.06

5.12

New Mexico

5.81

6.12

5.60

New York

5.57

4.29

11.29

5.01

North Carolina

8.29

6.17

14.62

6.32

North Dakota

6.44

5.63

Ohio

7.74

6.25

15.03

6.88

Oklahoma

7.85

7.52

13.91

5.09

Oregon

5.41

5.22

10.16

5.36

Pennsylvania

7.52

5.78

14.04

7.94

Rhode Island

6.47

4.28

10.56

7.77

South Carolina

8.30

6.04

12.97

5.87

South Dakota

7.15

5.59

Tennessee

8.37

6.54

15.36

6.47

Texas

6.22

5.48

11.69

5.61

Utah

4.94

4.73

5.03

Vermont

5.12

4.95

Virginia

7.24

5.48

13.40

5.97

Washington

5.01

4.33

7.66

5.28

West Virginia

7.38

7.11

14.93

Wisconsin

6.57

5.37

15.14

6.34

Wyoming

7.05

6.32

7.90

* Infant mortality rate = number of deaths among infants aged <1 year per 1,000 live births in a specific group.

Does not meet standards of reliability or precision; based on <20 deaths in the numerator.


FIGURE. Ratio of non-Hispanic black and non-Hispanic white infant mortality rates,* by state — United States, 2006–2008

This figure is a map of the United States that presents the ratio of infant mortality rates for non-Hispanic black and non-Hispanic white infants by state during 2006-2008, as reported by the National Vital Statistics System, the National Center for Health Statistics, and CDC.


Source: National Vital Statistics System, NCHS, CDC.

* Infant mortality rate = number of deaths among infants aged <1 year per 1,000 live births in a specific group.

Alternate Text: This figure is a map of the United States that presents the ratio of infant mortality rates for non-Hispanic black and non-Hispanic white infants by state during 2006-2008, as reported by the National Vital Statistics System, the National Center for Health Statistics, and CDC.


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