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Neonatal and Infant Weight-Specific Mortality Rates -- New Mexico

As recent studies have indicated, underreporting of neonatal deaths may occur when neonatal mortality rates are below 750 per 1,000 live births in the 500-1,000 g birth-weight range (1-3). In a current study, neonatal* and infant** weight-specific mortality rates for New Mexico were computed from that state's vital statistics data. No significant underreporting was found.

New Mexico recorded 87,724 births from 1974 through 1977. Of 1,438 recorded infant deaths, 1,364 (95%) were matched with corresponding birth records. Accuracy of neonate and infant classifications in the New Mexico records was checked by comparing vital statistics codes with a computer calculation of age at death (day, month, and year of birth were subtracted from day, month, and year of death (4)). In only nine instances was age at death coded as neonatal when it should have been postneonatal, or vice versa. Tables 1 and 2 show the New Mexico rates plus corrected neonatal mortality rates for Georgia, 1974-1976 (2), infant mortality rates for New York City, 1968 (5), and neonatal and infant mortality rates for the United States, 1960 (6). To assess relative differences in rates for various areas, 95% confidence intervals were constructed for each birth-weight category*** (7). *Less than 28 days of age **Less than 365 days of age ***Although previous studies have reported weight-specific mortality rates in grams, New Mexico's weights were reported in pounds and ounces; thus, the data here are given in both systems.

Neonatal mortality rates for New Mexico did not differ statistically in any of the five weight-specific categories from the corresponding corrected rates for Georgia. Similarly, infant mortality rates for New Mexico did not differ statistically in the first four weight-specific categories from the corresponding rates for New York City. In the over-2500-g category, the infant mortality rate from New Mexico was statistically distinct from that of New York City. Although the difference was not large, it was important because 90% of the births occurred in this category. In the unknown-weight category, New Mexico's rate was statistically different from Georgia's for neonates and from New York City's for infants. The total neonatal mortality rate (data for all known and unknown birth weights combined) for New Mexico differed statistically from that for Georgia, and the total infant mortality rate for New Mexico differed statistically from that for New York City. This shows the effects of the unknown category and of the differential composition of each birth-weight category on the total mortality rate. For New York City, it may also reflect the 6-year lag between the study in that city and the New Mexico study.

U.S. mortality rates for both neonates and infants in all weight-specific categories and totals were significantly higher for 1960 than were the corresponding rates from the later studies in New Mexico, Georgia, and New York City, presumably because of improved standards of living, medical technology, and public health. Reported by RG Rogers, Population Research Center, University of Texas, Austin, Texas; MW Ammann, AA Ortiz, P Totkamachi, New Mexico Vital Statistics Bureau, Santa Fe, New Mexico.

Editorial Note

Editorial Note: Many studies of neonatal and infant mortality begin by reviewing and matching birth and death certificates and then verifying the data with computer tape records. The New Mexico study was done in reverse. While some data may have been missed because they were miscoded or not entered on the tape, other records found on the tape were not filed with the birth and death certificates. Thus, it appears to make little difference which starting point is used.

A comparison of New Mexico's weight-specific mortality rates with those of the United States and New York City and corrected rates for Georgia uncovered no reason to follow-up any particular weight group in the New Mexico study. Moreover, New Mexico's neonatal mortality rate for the 500-1,000-g birth weight category exceeded the minimum rate of 750 deaths per 1,000 live births at which underreporting should be suspected (1).

For comparison purposes, investigators and public health officials in other states may use the baseline rates provided by this current study.


  1. CDC. Underreporting of neonatal deaths--Georgia, 1974-1977. MMWR 1979;28:253-4.

  2. McCarthy BJ, Terry J, Rochat RW, Quave S, Tyler CW Jr. The underregistration of neonatal deaths: Georgia 1974-77. Am J Public Health 1980;70:977-82.

  3. Rogers PB, Council CR, Abernathy JR. Testing death registration completeness in a group of premature infants. Public Health Rep 1961;76:717-24.

  4. Helwig JT, Council KA, eds. SAS user's guide. Raleigh, N.C.: SAS Institute, Inc. 1979.

  5. Institute of Medicine, Panel on Health Services Research. Infant death: an analysis of maternal risk and health care. Washington, D.C.: National Academy of Sciences, IOM, 1973:90 (Table 3-25).

  6. Department of Health, Education, and Welfare. A study of infant mortality from linked records (NCHS report, Series 20, No. 12). Washington, D.C.: Department of Health, Education, and Welfare, May 1972. (Births: Table 3, page 33; infant deaths: Table 1, page 27).

  7. Kleinman, JC. Infant mortality. Statistical Notes for Health Planners (NCHS) 1976;2:1-12.

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