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.
References
CDC. Underreporting of neonatal deaths--Georgia, 1974-1977.
MMWR
1979;28:253-4.
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.
Rogers PB, Council CR, Abernathy JR. Testing death registration
completeness in a group of premature infants. Public Health Rep
1961;76:717-24.
Helwig JT, Council KA, eds. SAS user's guide. Raleigh, N.C.:
SAS
Institute, Inc. 1979.
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).
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).
Kleinman, JC. Infant mortality. Statistical Notes for Health
Planners (NCHS) 1976;2:1-12.
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