Infant Mortality -- United States, 1993

The 1993 final infant mortality (death before age 1 year) rate for the United States -- 8.4 infant deaths per 1000 live-born infants -- was the lowest rate ever recorded and represented a decrease of 1.8% from the rate of 8.5 for 1992. Based on provisional data for 1994, the declining trend in infant mortality continued through 1994 (rate: 7.9) (1). This report uses data from birth and death certificates compiled by CDC (2) to characterize infant mortality in 1993 and compares the findings with those for 1992.

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. Because race reflects differing distributions of several risk factors for infant death (e.g., low birthweight {LBW} {less than 2500 g (less than 5 lbs 9 oz) at birth}) and is useful for identifying groups at greatest risk for infant death, this analysis examines race-specific mortality rates. Numerators for infant mortality rates (infant deaths) were tabulated by race of infant; denominators for rates (live-born infants) were tabulated by race of mother. Rates are presented only for white and black 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 1992 and 1993. Numbers for white and black infants include both Hispanic and non-Hispanic infants.

In 1993, a total of 34,466 infants died in the United States, compared with 38,910 in 1992. The mortality rate for white infants in 1993 (6.8 per 1000) decreased 1.4% from the rate in 1992 (6.9), and the rate for black infants in 1993 (16.5) decreased 1.9% from the rate in 1992 (16.8).

Declines in race-specific rates also varied by age at death. From 1992 through 1993, the overall neonatal mortality (death before age 28 days) rate decreased 1.9% (5.4 to 5.3); for white infants, the rate remained constant (4.3), and for black infants, the rate decreased 1.0% (10.8 to 10.7). The overall postneonatal mortality (death at age 28 days-11 months) rate decreased 2.2% (3.1 to 3.0 per 1000); for white infants, the rate decreased 4% (2.6 to 2.5), and for black infants, 3.5% (6.0 to 5.8). In 1993, the risk for death during the first year of life for black infants remained 2.4 times greater than for white infants.

Among the 10 leading causes of infant death, the first four (congenital anomalies, sudden infant death syndrome, disorders relating to short gestation and unspecified LBW, and respiratory distress syndrome {RDS}) accounted for 54% of all infant deaths in 1993 (Table_1). For white infants, these causes also accounted for 54% of deaths, and for black infants, 51% of deaths.

From 1992 to 1993, the infant mortality rate decreased for seven of the 10 leading causes of infant death and increased for three causes (Table_1). For white infants, the rate also decreased for seven of the 10 causes; however, for blacks, the rate decreased for six of the 10 causes. Race-specific differences in infant mortality also were reflected in the rank order of the leading causes of infant death and in the rate of change of specific causes (Table_1). For white infants, the largest decrease in rates was for RDS (International Classification of Diseases, Ninth Revision {ICD-9}, code 769) (15.5%), and the largest increase, disorders relating to short gestation and LBW (ICD-9 code 765) (16.1%). For black infants, the largest decrease was for pneumonia and influenza (ICD-9 codes 480-487) (16.8%), and the largest increase, infections specific to the perinatal period (ICD-9 code 771) (9.3%). The decrease in RDS for black infants was less than 1%.

Reported by: Div of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion; Mortality Statistics Br, Div of Vital Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: The infant mortality rate is a standard index of health. In 1991 (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 greater than or equal to 1 million (3). Two national health objectives for the year 2000 are 1) to reduce the overall infant mortality rate to no more than 7 per 1000 (objective 14.1) and 2) to reduce the rate among black infants to no more than 11 per 1000 (objective 14.1a) (4). Based on the findings for 1993, attaining these goals will require an average annual decrease of 2.6% in the overall infant mortality rate and a 3.6% annual decrease in the rate for black infants.

In 1993, disorders relating to short gestation and unspecified LBW was the third leading cause of infant death overall, and the leading cause for black infants. During 1992-1993, mortality rates for this cause increased 8.4%, and during 1985-1993 increased 24%. However, based on data about infant birthweight or gestational age available in linked birth and infant death files, recent reductions in the misclassification of infant deaths to this cause may have obfuscated the true increase. If the number of deaths from disorders relating to short gestation and unspecified LBW continue to increase, the year 2000 objectives may not be attained.

The increased role of disorders relating to short gestation and unspecified LBW may reflect the 7.2% increase in LBW infants during 1992-1993 (5). A large portion of the increase in LBW infants has been attributed to increases in the rate of multiple births to white women and sustains a trend since 1980 (6). During 1985-1991, the proportion of deaths attributed to short gestation and unspecified LBW accounted for by multiple births increased from 5.6% to 11.5% -- more than doubling for both white infants and black infants; however, this increase reflects primarily a large increase in the cause-specific infant mortality rate for whites (16.1%) (the rate for blacks increased only 2.0%). In comparison, during this period, infant mortality rates decreased for other causes associated with LBW (i.e., RDS, newborn affected by maternal complications of pregnancy, and congenital anomalies).

Although the total infant mortality rate declined in 1993, differences persisted in race-specific rates. This pattern underscores the need to distinguish between the factors associated with the decline and those associated with the race-specific differences. Reasons have not been determined for the lack of progress in reducing the infant mortality rates and race-specific differences associated with short gestation and LBW. Improved understanding of the heterogeneity of the risk factors that account for infant mortality and race-specific differentials associated with short gestation and LBW is essential for the development of prevention strategies aimed at reducing these differences. Differences in socioeconomic status and access to health care account for only a portion of the race-specific mortality differences (7,8), indicating the need for examination of information on other factors that may not be available from routinely collected data.

References

1. NCHS. Annual summary of births, marriages, divorces, and deaths: United States, 1993. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1994. (Monthly vital statistics report; vol 42, no. 13).

2. NCHS. Advance report of final mortality statistics, 1992. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1994. (Monthly vital statistics report; vol 43, no. 2, suppl).

3. NCHS. Health, United States, 1994. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1995; DHHS publication no. (PHS)95-1232.

4. 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.

5. NCHS. Advance report of final natality statistics, 1993. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1995. (Monthly vital statistics report; vol 44, no. 3, suppl).

6. Martin JA, Taffel SM. Current and future impact of rising multiple birth ratios on low birth weight. In: MetLife. Statistical bulletin. New York, New York: Metropolitan Life Insurance Co, 1995 (April-June issue).

7. Schoendorf KC, Hogue CJR, Kleinman JC, Rowley D. Mortality among infants of black as compared with white college-educated parents. N Engl J Med 1992;326:1522-6.

8. CDC. Poverty and infant mortality -- United States, 1988. MMWR 1995;44:922-7.

* Defined by the International Classification of Diseases, Ninth Revision, 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."

TABLE 1. Number of infant deaths *, mortality rate +, and percentage change from 1992 to 1993, and
percentage of deaths attributed to the 10 leading causes of death, by race & of mother and cause
-- United States, 1993
======================================================================================================
                                                                      % Change in
Race/Rank                                                              rate from         %
 order @  Cause of death (ICD-9 ** codes)                No.    Rate  1992 to 1993  Distribution
------------------------------------------------------------------------------------------------------
BLACK
 1        Disorders relating to short gestation
           and unspecified low birthweight (765)        2,021   306.7      2.0        18.6
 2        Sudden infant death syndrome (798.0)          1,442   218.9      0.2        13.3
 3        Congenital anomalies (740-759)                1,403   212.9    - 2.9        12.9
 4        Respiratory distress syndrome (769)             686   104.1    - 0.6         6.3
 5        Newborn affected by maternal
           complications of pregnancy (761)               452    68.6    - 0.9         4.2
 6        Newborn affected by complications
           of placenta, cord, and membranes (762)         315    47.8      8.1         3.2
 7        Infections specific
           to the perinatal period (771)                  272    41.3    - 9.1         2.5
 8        Accidents++ and adverse effects (E800-E949)     259    39.3      5.4         2.4
 9        Pneumonia and influenza (480-487)               176    26.7    -16.8         1.6
10        Intrauterine hypoxia and birth asphyxia (768)   158    24.0    -12.7         1.5
          All other causes (residual)                   3,703   562.0    - 4.1        34.0
All causes                                             10,887 1,652.4    - 1.9       100.0

WHITE
 1        Congenital anomalies                          5,449   173.0    - 2.3        25.4
 2        Sudden infant death syndrome                  3,056    97.0    - 4.2        13.3
 3        Disorders relating to short gestation
           and unspecified low birthweight              2,202    69.9     16.1        10.2
 4        Respiratory distress syndrome                 1,098    34.9    -15.5         6.3
 5        Newborn affected by maternal
           complications of pregnancy                     869    27.6    - 8.3         4.2
 6        Newborn affected by complications
           of placenta, cord, and membranes               649    20.6      0           3.2
 7        Accidents and adverse effects                   599    19.0     14.5         2.4
 8        Infections specific to the perinatal period     481    15.3    -14.5         2.2
 9        Intrauterine hypoxia and birth asphyxia         371    11.8    - 6.4         1.7
10        Pneumonia and influenza                         323    10.3    - 8.0         1.5
          All other causes (residual)                   6,400   203.2    - 0.3        29.8
All causes                                             21,497   682.5    - 1.4       100.0

TOTAL &&
 1        Congenital anomalies                          7,129   178.2    - 2.7        21.3
 2        Sudden infant death syndrome                  4,669   116.7    - 3.0        14.0
 3        Disorders relating to short gestation
           and unspecified low birthweight              4,310   107.7      8.5        12.9
 4        Respiratory distress syndrome                 1,815    45.4    -10.6         5.4
 5        Newborn affected by maternal
           complications of pregnancy                   1,314    33.6    - 6.4         4.0
 6        Newborn affected by complications
           of placenta, cord, and membranes               994    24.8      1.6         3.0
 7        Accidents and adverse effects                   898    22.4     11.4         2.7
 8        Infections specific to the perinatal period     772    19.3    -13.1         2.3
 9        Intrauterine hypoxia and birth asphyxia         549    13.7    - 9.3         1.6
10        Pneumonia and influenza                         530    13.2    -10.8         1.6
          All other causes (residual)                  10,457   261.4    - 1.7        31.2
All causes                                             33,466   836.6    - 1.8       100.0
------------------------------------------------------------------------------------------------------
*  Death before age 1 year.
+  Per 100,000 live-born infants in specified group.
&  Race differences are given 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 1992 and 1993. Hispanics and non-Hispanics are included in both racial
   groups.
@  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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