According to national death certificate data (Table V) (1), three of the 13 leading causes of years of potential life lost before age 65 (YPLL)--congenital anomalies, prematurity, and sudden infant death syndrome--occur primarily in the first year of life. Deaths are attributed to prematurity in Table V if the underlying cause is classified as category 765 or 769 according to The International Classification of Diseases, 9th Revision (ICD-9). This definition of prematurity includes infants with one or more of the following three conditions: low birthweight (2,500 grams), preterm delivery (gestation 37 completed weeks), and respiratory distress syndrome.

The Table V definition, however, underestimates the total YPLL attributable to low birthweight because low birthweight also increases the risk of death from other perinatal conditions* and from all other causes of infant mortality (2). By analyzing cause- and birthweight-specific mortality data for 1980 from the National Infant Mortality Surveillance (NIMS) project, CDC found that 82.4% of YPLL for perinatal conditions was attributable to low birthweight (2). The NIMS data showed that less than half the YPLL for perinatal conditions resulted solely from the causes of death included in the Table V definition of prematurity. Thus, YPLL for perinatal conditions may be a more comprehensive estimate of YPLL attributable to low birthweight.

In the analysis for 1980-1983 reported here, all infant deaths (1 year of life) in the United States were examined using numbers and underlying causes of death from the National Center for Health Statistics (NCHS) national mortality computer tapes. Underlying causes of death were divided into two groups, perinatal conditions and other causes, by modifying previously described classification schemes (Table 2) (2,3). YPLL was calculated by averaging age at death for each subgroup** for the period 1980-1983, the latest year for which data are available.

For 1980-1983, the average annual YPLL due to all causes of infant death was 2,787,465; 1,861,691 YPLL (66.8%) occurred because of deaths in the neonatal period (28 days), and 925,774 YPLL, because of deaths in the postneonatal period (28 days to 1 year). During this same period, 46.7% of YPLL in the first year of life was due to perinatal conditions; 95.9% occurred in the neonatal period, and 4.1%, in the postneonatal period.

The average YPLL due to perinatal conditions during this 4-year period was 1,300,530. During this same period, the average annual race- and sex-specific YPLL was 501,901 for white males, 368,027 for white females, 240,042 for males of black and other races, and 190,560 for females of black and other races. The male to female ratio for white infants was 1.4:1, compared with 1.3:1 for infants of black and other races.

YPLL depends directly on the number of births in any given group. The average annual YPLL due to perinatal conditions per 1,000 live births was 335.3 for white males, 259.8 for white females, 649.9 for males of black and other races, and 533.1 for females of black and other races.

The percentage of low birthweight births was approximately 6.8% for each year during the period 1980-1983. Because the percentage was about the same for each year during this 4-year period, 82.4% of the total YPLL due to perinatal conditions (as determined in the NIMS study for 1980) is probably due to low birthweight for each year. Consequently, the YPLL attributable to low birthweight was estimated at 1,150,162 for 1980, 1,102,697 for 1981, 1,055,552 for 1982, and 978,135 for 1983. The total YPLL for each cause of death in 1980 is greater in Table 2 than in the NIMS study because the NIMS project included only singleton births of known birthweight and 95% of the reported deaths. Reported by: Pregnancy Epidemiology Br, Research and Statistics Br, Div of Reproductive Health, Center for Health Promotion and Education, CDC.

Editorial Note

Editorial Note: There are two causes of low birthweight: preterm delivery and intrauterine growth retardation (IUGR). As a result, there are three groups of low birthweight infants: 1) term infants who are small for their gestational age ( greater than or equal to 37 weeks, 2,500 grams); 2) preterm infants who are appropriate in size for their gestational age (37 weeks, greater than the tenth percentile by weight for gestational age); and 3) preterm infants who are small for their gestational age (37 weeks, less than the tenth percentile by weight for gestational age). The first group of low birthweight infants are a result of IUGR; the second, of preterm delivery; and the third, of both IUGR and preterm delivery. It is important to distinguish between preterm delivery and IUGR as causes of YPLL due to perinatal conditions because they are associated with different levels of risk. Moreover, preterm delivery and IUGR may have different etiologies that will require different strategies for prevention.

The male excess in YPLL due to perinatal conditions per 1,000 live births (29% for whites and 22% for blacks and other races) occurs despite their lower risk of low birthweight. Much of this excess risk of death is related to a higher risk of death from respiratory distress syndrome, which accounted for 1.5 deaths per 1,000 male live births in 1983 but for 1.0 deaths per 1,000 female live births.

The rate of YPLL due to perinatal conditions per 1,000 live births for blacks is 2.3 times that for whites. This is related primarily to the higher risk of low birthweight for black infants, since the risk of birthweight-specific mortality among low birthweight black infants is lower than the risk of birthweight-specific mortality among white infants (4). Reducing this gap is dependent upon the prevention of low birthweight.

References

1. CDC. Introduction to table V: premature deaths, monthly mortality, and monthly physician contacts--United States. MMWR 1982;31:109-10,117.

2. CDC. Years of potential life lost attributable to low birthweight--United States, 1980 birth cohort. MMWR 1986;35:188-90,195.

3. Buehler JW, McCarthy BJ, Holloway JT, Sikes RK. Infant mortality in a rural health district in Georgia, 1974 to 1981. South Med J 1986;79:444-50.

4. Hogue CJR, Buehler JW, Strauss LT, Smith JC. Overview of the design, methods, and results of the National Infant Mortality Surveillance (NIMS) project. Public Health Rep (in press). *Conditions occurring in the first year of life and classified as ICD-9 codes 760-779, excluding perinatal infections. **YPLL = T(65-(A/365.25)), where T = total number of infant deaths for subgroup (age, sex, race, year, and cause of death) and A = average age at death in days for that subgroup.

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