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Infant Mortality -- United States, 1991

The final infant (less than 1 year of age) mortality rate for the United States for 1991 -- 8.9 infant deaths per 1000 live births -- was the lowest rate ever recorded and represented a decrease of 3% from the rate of 9.2 for 1990 (Figure_1). Based on provisional data, the trend of declining infant mortality continued through 1992 (rate: 8.5) (1). Infant mortality rates varied by race; race reflected differing distributions of several risk factors for infant death (e.g., low birthweight {LBW} {less than 2500 g (5 lbs 9 oz) at birth}) and is useful for identifying groups at greatest risk for infant death. This report uses race-specific information from birth and death certificates compiled by CDC's National Center for Health Statistics' Vital Statistics System (2) to characterize infant mortality in 1991 and compares findings with those for 1990.

In this report, cause-of-death statistics are based on the underlying cause of death * reported on the death certificate by the attending physician, medical examiner, or coroner in a manner specified by the World Health Organization. Race for infants who died was tabulated by race of infant; race for live births (which comprise the denominator of infant mortality rates) was tabulated by race of mother. Rates are presented only for black and white infants because the Linked Birth/Infant Death Data Set (used to more accurately estimate infant mortality rates for other racial groups) was not available for 1990 and 1991.

A total of 36,766 infants died during 1991, compared with 38,351 during 1990. The mortality rate for white ** infants in 1991 (7.3 per 1000) decreased 4% from the rate in 1990 (7.6); for black ** infants, the difference between the rates for 1990 and 1991 was not statistically significant (18.0 and 17.6, respectively). From 1990 to 1991, the neonatal ( less than 28 days of age) mortality rate decreased 3% (5.8 to 5.6 per 1000). For white infants, the rate decreased from 4.8 to 4.5 and for black infants, from 11.6 to 11.2. The postneonatal (28 days-11 months of age) mortality rate remained constant at 3.4 in 1990 and 1991.

From 1990 to 1991, the infant mortality rate decreased for six of the 10 leading causes of infant death and increased for three causes (Table_1). The largest decreases were for intrauterine hypoxia and birth asphyxia (International Classification of Diseases, Ninth Revision {ICD-9}, code 768) (20%), respiratory distress syndrome (RDS) (ICD-9 code 769) (9%), and congenital anomalies (ICD-9 codes 740-759) and newborn affected by maternal complications of pregnancy (ICD-9 code 761) (6% each). The increases were for disorders relating to short gestation and unspecified LBW (ICD-9 code 765) (4%), accidents *** and adverse effects (ICD-9 codes E800-E949) (4%), and infections specific to the perinatal period (ICD-9 code 771) (2%).

The rank order of the 10 leading causes of infant death differed by race (Table_1). Although the first four leading causes of death were the same for white and black infants, their rank ordering differed; these same four causes accounted for 56% and 50% of all deaths among white and black infants, respectively. For white infants, the leading cause of death was congenital anomalies, which accounted for 25% of all deaths among white infants; for black infants, the leading cause of death was disorders relating to short gestation and unspecified LBW, which accounted for 16% of all deaths among black infants.

In 1991, the risk for dying during the first year of life was 2.4 times greater for black than for white infants. For each of the leading causes of death, the risk for death was higher for black than for white infants, although there were large variations in the magnitude of the excess by cause. The cause-specific ratios were highest for disorders relating to short gestation and unspecified LBW (4.4:1), pneumonia and influenza (ICD-9 codes 480-487) (3.2:1), RDS (2.6:1), infections specific to the perinatal period (2.6:1), and newborn affected by maternal complications of pregnancy (2.5:1). The ratios were lowest for sudden infant death syndrome (SIDS) (ICD-9 code 798.0); newborn affected by complications of placenta, cord, and membranes (ICD-9 code 762); and accidents and adverse effects (2.1:1 each) and congenital anomalies (1.2:1). Three of the 10 leading causes of infant death accounted for 42% of the difference in infant mortality between black and white infants: disorders relating to short gestation and unspecified LBW (22%), SIDS (12%), and RDS (8%). Reported by: Mortality Statistics Br, Div of Vital Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: The infant mortality rate -- a standard index of health -- is higher in the United States than in many other developed countries. In 1989 (the most recent year for which comparative data are available), the U.S. infant mortality rate ranked 24th among countries or geographic areas with a population of at least 1 million (3), a decline in rank from 1980 (20th) (4).

The U.S. infant mortality rate declined by approximately 5% per year during the 1970s, but slowed to an annual average decrease of 3% during the 1980s. The decline of 6% from 1989 to 1990 primarily reflected a 24% decrease in mortality from RDS. From 1990 to 1991, the infant mortality rate declined by 3%; more than half of this decrease represented declines in mortality from congenital anomalies (35%) and RDS (19%). The decline in mortality from congenital anomalies (6% overall) was primarily among whites; mortality from congenital anomalies remained constant among blacks. Shifts in the age distribution of mothers between 1990 and 1991 may account for some of the decline in mortality from congenital anomalies (5). The decline in mortality from 1990 to 1991 from RDS may reflect improvements in medical management of this condition (6).

Differences in infant mortality rates by race may reflect differences in factors such as socioeconomic status, access to medical care, and the prevalence of specific risks. For example, the mortality rate is substantially higher for infants born to mothers of low socioeconomic status (7). In 1990, nearly three times as many black as white infants (56% versus 20%) were members of families with incomes below the poverty level (Bureau of the Census, unpublished data, 1992). In addition, because of income differentials, a lower proportion of black women have health insurance that covers the costs of adequate care for pregnancy and childbirth (6,8).

LBW is an important intermediate variable between some risk factors and infant mortality. In 1987 (the most recent year for which such data were available), 6.9% of infants were born with LBW; however, 61% of all infant deaths occurred among these infants. In 1991, 13.6% of black infants were born with LBW, compared with 5.8% of white infants (6). Most of the causes of death for which black infants are at substantially elevated risk for death are closely associated with LBW. For three of the four causes of infant death characterized by the highest ratios of black-to-white mortality rates (i.e., disorders relating to short gestation and unspecified LBW, RDS, and newborn affected by maternal complications of pregnancy), approximately 95% of the deaths in 1987 occurred among LBW infants (CDC, unpublished data, 1992).

The 1990 national health objective to reduce the overall infant mortality rate to 9.0 deaths per 1000 live births (9) was achieved in 1991 (recorded rate: 8.9). A year 2000 national health objective is to reduce the overall infant mortality rate to no more than 7.0 per 1000 live births (objective 14.1) (9). This objective can be achieved by sustaining an average annual decrease of at least 2.4% for the total population.

Strategies to achieve the national health objective for reducing infant mortality should consider the heterogeneity of factors accounting for infant mortality in the United States. For example, reducing mortality from disorders related to short gestation and unspecified LBW will require both improved access to adequate prenatal care and understanding of etiologic risk factors for preterm delivery; reduction of deaths related to maternal complications of pregnancy will require both expansion of access to prenatal care and assessment of the adequacy of the content of care (10). Efforts to address these and other heterogenous risk factors may increase the likelihood of achieving the year 2000 national health objective to reduce infant mortality.

References

  1. NCHS. Annual summary of births, marriages, divorces, and deaths: United States, 1992. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1993. (Monthly vital statistics report; vol 41, no. 13).

  2. NCHS. Advance report of final mortality statistics, 1991. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1993. (Monthly vital statistics report; vol 42, no. 2, suppl).

  3. NCHS. Health, United States, 1992. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1993; DHHS publication no. (PHS)93-1232.

  4. NCHS. Health, United States, 1988. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1989; DHHS publication no. (PHS)89-1232.

  5. NCHS. Advance report of final natality statistics, 1991. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1993. (Monthly vital statistics report; vol 42, no. 3, suppl).

  6. Long W, Corbet A, Cotton R, et al. A controlled trial of synthetic surfactant in infants weighing 1250 g or more with respiratory distress syndrome. N Engl J Med 1991;325:1696-703.

  7. Gould JB, Davey B, LeRoy S. Socioeconomic differentials and neonatal mortality: racial comparison of California singletons. Pediatrics 1989;83:181-6.

  8. Alan Guttmacher Institute. Blessed events and the bottom line: financing maternity care in the United States. New York: Alan Guttmacher Institute, 1987.

  9. Public Health Service. Healthy people 2000: national health promotion and disease prevention objectives -- full report, with commentary. Washington, DC: US Department of Health and Human Services, Public Health Service, 1991; DHHS publication no. (PHS)91-50212.

  10. Public Health Service. Caring for our future: the content of prenatal care -- a report of the Public Health Service Expert Panel on the Content of Prenatal Care. Washington, DC: US Department of Health and Human Services, Public Health Service, 1989.

* Defined by the World Health Organization's International Classification of Diseases, Ninth Revision (ICD-9), as "(a) the disease or injury which initiated the train of morbid events leading directly to death, or (b) the circumstances of the accident or violence which produced the fatal injury." 

** Includes Hispanic and non-Hispanic infants. 

*** When a death occurs under "accidental" circumstances, the preferred term within the public health community is "unintentional injury."
Figure_1

Figure_1
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Table_1
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TABLE 1. Number of infant deaths, mortality rate, * and percentage of deaths for each
cause, by race + of mother -- United States, 1991
===================================================================================================
Race/Rank                                                                                 %
order &     Cause of death (ICD-9 @ codes)                          No.      Rate    Distribution
-------------------------------------------------------------------------------------------------
BLACK
  1         Disorders relating to short gestation
              and unspecified low birthweight (765)                1,957     286.7       16.3
  2         Sudden infant death syndrome (798.0)                   1,589     232.8       13.2
  3         Congenital anomalies (740-759)                         1,524     223.3       12.7
  4         Respiratory distress syndrome (769)                      898     131.6        7.5
  5         Newborn affected by maternal complications
              of pregnancy (761)                                     519      76.0        4.3
  6         Infections specific to the perinatal period (771)        304      44.5        2.5
  7         Newborn affected by complications of placenta,
              cord, and membranes (762)                              290      42.5        2.4
  8         Accidents ** and adverse effects (E800-E949)             276      40.4        2.3
  9         Pneumonia and influenza (480-487)                        234      34.3        2.0
 10         Intrauterine hypoxia and birth asphyxia (768)            190      27.8        1.6
            All other causes (residual)                            4,213     617.2       35.1
All causes                                                        11,994   1,767.1      100.0

WHITE
  1         Congenital anomalies (740-759)                         5,864     180.9       24.8
  2         Sudden infant death syndrome (798.0)                   3,572     110.2       15.1
  3         Disorders relating to short gestation
              and unspecified low birthweight (765)                2,097      64.7        8.9
  4         Respiratory distress syndrome (769)                    1,622      50.0        6.9
  5         Newborn affected by maternal complications
              of pregnancy (761)                                     988      30.5        4.2
  6         Newborn affected by complications of placenta,
              cord, and membranes (762)                              643      19.8        2.7
  7         Accidents ** and adverse effects (E800-E949)             638      19.7        2.7
  8         Infections specific to the perinatal period (771)        556      17.2        2.4
  9         Intrauterine hypoxia and birth asphyxia (768)            397      12.2        1.7
 10         Pneumonia and influenza (480-487)                        346      10.7        1.5
            All other causes (residual)                            6,934     213.9       29.3
All causes                                                        23,657     729.9      100.0

TOTAL ++
  1         Congenital anomalies (740-759)                         7,685     186.9       20.9
  2         Sudden infant death syndrome (798.0)                   5,349     130.1       14.5
  3         Disorders relating to short gestation
              and unspecified low birthweight (765)                4,139     100.7       11.3
  4         Respiratory distress syndrome (769)                    2,569      62.5        7.0
  5         Newborn affected by maternal complications
              of pregnancy (761)                                   1,536      37.4        4.2
  6         Newborn affected by complications of placenta,
              cord, and membranes (762)                              962      23.4        2.6
  7         Accidents ** and adverse effects (E800-E949)             961      23.4        2.6
  8         Infections specific to the perinatal period (771)        881      21.4        2.4
  9         Pneumonia and influenza (480-487)                        607      14.8        1.7
 10         Intrauterine hypoxia and birth asphyxia (768)            599      14.6        1.6
            All other causes (residual)                           11,478     279.2       31.2
All causes                                                        36,766     894.4      100.0
-------------------------------------------------------------------------------------------------
 * Deaths at <1 year of age, per 100,000 live births in specified group.
 + Race differences are presented only for black and white infants because the Linked
   Birth/Infant Death Data Set (used to more accurately estimate infant mortality rates for other
   racial groups) was not available for 1990 and 1991.
 & Based on number of deaths.
 @ International Classification of Diseases, Ninth Revision.
** When a death occurs under "accidental" circumstances, the preferred term within the public
   health community is "unintentional injury."
++ Includes races other than black and white.
===================================================================================================


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