Michele C. Lynberg, Ph.D., M.P.H.
Muin J. Khoury, M.D., Ph.D.
Birth Defects and Genetic Disease Branch
Division of Birth Defects and Developmental Disabilities
Center for Environmental Health and Injury Control
Linked birth/infant death data from the National Center for
Health Statistics (NCHS) for the 1983 U.S. birth cohort, the
latest year for which linked data were available, were evaluated
in order to assess the contribution of birth defects to infant
mortality among racial/ethnic groups. Of the 34,566 singleton
infant deaths with specified birth weight born to U.S. residents,
birth defects were listed as an underlying cause of death for
7,678 (22.2%) infants and as a contributing cause of death for an
additional 1,006 (2.9%) infants. Infant mortality rates due to
birth defects were highest among American Indians (2.9
deaths/1,000 live births), followed by Asians and Hispanics
(2.6), and blacks (2.5). Proportional mortality due to birth
defects varied among racial/ethnic groups; it was greatest among
Asians (27%), followed by whites (25%), Hispanics (24%), American
Indians (18%), and blacks (13%). Also, infant mortality rates due
to birth defects were high among minority infants of low birth
weight, particularly among those born weighing between 1,500 and
2,499 g. Within this group of infants, proportional mortality due
to birth defects ranged from 52% among Asians to 29% among
blacks. These data indicated that birth defects were an important
contributor to infant mortality among all racial/ethnic groups.
Birth-defects surveillance systems should be used to evaluate
whether racial/ethnic differences in infant mortality from birth
defects are due to differences in incidence and/or survival among
minority infants with birth defects.
Birth defects are the leading cause of infant mortality in the
United States (1) and the fifth leading cause of years of
potential life lost (YPLL) (2). Also, birth defects contribute
substantially to childhood morbidity and long-term disability.
Approximately 80,000 infants are born with a major birth defect
in the United States each year. Of these, approximately 6,000 die
during the first 28 days of life, and another 2,000 die before
reaching their first birthday, leaving 72,000 living children
affected to various degrees (3). Children with birth defects
account for approximately 25%-30% of pediatric hospital
admissions; total costs for care of children with birth defects
exceed $1 billion annually (4,5). Using reported age-specific
survival rates and age-specific medical-care costs, CDC estimates
that $90 million (based on the 1985 value of the dollar) will be
spent on medical care in 1990 for 12,000 surviving infants with
spina bifida born since 1980 (6).
All segments of the U.S. population share the burden of birth
defects, with frequency and type varying by race, ethnicity, and
socioeconomic status (7-11). Between 1981 and 1986, American
Indians showed the highest incidence rates of major defects per
1,000 total births (22.0). Other minorities had lower rates:
blacks (18.0), Hispanics (14.4), and Asians (15.8) (12). In
comparison, the incidence of major defects was 19.0/1,000 live
births among whites.
This report summarizes the contribution of birth defects to
infant mortality among racial/ethnic minorities.
Information on birth and death data was obtained from NCHS'
linked birth/infant death data set for the 1983 birth cohort,
which consists of two separate data files (13). Information on
births and deaths was obtained from NCHS' natality statistical
file and NCHS' mortality statistical file. The numerator file
contained information from birth and death certificates
concerning infants born in 1983 who died in 1983 or 1984 before
their first birthday. The denominator file included information
from birth certificates concerning all live births for 1983. Each
record contained information coded from birth and death
certificates supplied by each state. Information was available on
3,341,274 live births and 39,704 infant deaths. The analysis was
limited to singleton infants with known birth weight born to U.S.
Birth-certificate information included information on residence;
birth weight; gestational age; sex; race of baby, mother, and
father; origin (or descent) of mother; plurality; and other
information on pregnancy history. Death-certificate information
included data on underlying and contributing causes of death. In
addition, age of death, autopsy, and other identifying
information was available.
Mother's race and ethnicity were used to classify infants into
racial/ethnic minority groups. Twenty-three states and the
District of Columbia reported racial/ethnic origin on the birth
certificate. These reporting areas represented 96% of the
Hispanic population. Although the remaining states did not have
ethnic information included on the birth certificate, the
mother's reported place of birth permitted the further
identification of persons of Hispanic descent (those born in
Mexico, Puerto Rico, or Cuba). Using mother's descent--in
combination with mother's place of birth--permitted the
delineation of Hispanic individuals who would otherwise have been
classified as white.
Infants whose mothers were either of African descent or of the
black race were grouped into the category "black." The category
"American Indian" included American Indians, Aleuts, Eskimos,
Alaskans, and Canadian Indians. "Asian" included Chinese,
Japanese, Hawaiians, Filipinos, and other Asian or Pacific
Islanders. Infants whose mothers reported other descent (Northern
European, French, etc) or indicated they were white were included
in the category "white." Only 162 (0.5%) infants had "unknown"
race/ethnicity, and 13 infants were classified as "other" races.
These 175 infants were excluded from the minority-group analysis.
Causes of infant mortality were coded using the International
Classification of Diseases, 9th Revision (ICD-9). Table 1 details
the ICD-9 codes included in each of the underlying cause groups.
Birth defects were defined as conditions coded from 740.0 to
759.9 of the ICD-9. Conditions included in this group were
heterogeneous, including defects in all organ systems with
varying degrees of severity. Some "birth defects" are a result of
being born prematurely, and are not birth defects per se. Among
infants with low birth weight (LBW) (i.e., less than 2,500 g),
the authors looked for birth defects that could have been a
result of prematurity. These conditions were lung hypoplasia
(748.5), patent ductus arteriosus (747.0), and hydrocephalus
(742.3) associated with intraventricular hemorrhage (772.1). When
these conditions were associated with LBW infants, they were not
considered to be birth defects. Of 34,566 infants who died in
their first year of life, 1,037 had at least one of these three
types of "false" birth defects. Of these, 495 had other birth
defects as well, whereas 542 had false birth defects as their
only birth defects listed. False birth defects were listed as the
underlying cause of death for 353 infants. For these infants, the
underlying cause of death was reassigned.
When describing the occurrence of birth defects among premature
infants, the authors looked not only at deaths among infants with
unspecified LBW (ICD-9 765, disorders relating to short gestation
and unspecified LBW), but also specified LBW (ICD-9 764) and
respiratory distress syndrome (RDS) (ICD-9 769). Technically,
only premature infants can have RDS (or hyaline membrane
disease). Although some of the infants with ICD-9 code 769 may
have had respiratory distress unassociated with prematurity, we
had no means of separating them from those having RDS associated
with prematurity. In this analysis, the authors considered
infants with the RDS code as premature. For some analyses,
infants with an underlying cause of RDS, LBW, or prematurity were
grouped into one category.
Table 2 shows the number of live births and infant deaths by
race/ethnicity. Blacks had the highest infant mortality rate
(18.5 deaths/1,000 live births); American Indians had the next
highest rate (15.8/1,000 live births). All minority groups
exceeded the 1990 objective of nine infant deaths/1,000 live
Figure 1 shows that, overall, birth defects were the leading
cause of death in the 1983 birth cohort. Of 34,566 singleton
infant deaths with known birth weight, 7,678 (22.2%) were
attributed to birth defects. Low birth weight, prematurity, and
RDS combined were the cause of death for 5,654 (16.4%). Sudden
infant death syndrome (SIDS) was the cause of death for 5,049
Birth defects that contributed most to infant mortality, grouped
by organ system, are shown in Table 3. Regardless of the
racial/ethnic group, cardiovascular-system defects were the most
commonly recorded defects on the death certificate.
Central-nervous-system defects and chromosomal anomalies were
In Figures 2-4, infant mortality rates, as well as the
proportional mortality due to the three leading underlying causes
of infant death, are shown. The underlying cause of death, by
racial/ethnic group, is shown in Figure 2. Birth defects were the
leading cause of infant mortality among Hispanics, Asians, and
whites. Prematurity, LBW, and RDS combined were the leading
causes of infant mortality among blacks, whereas SIDS was the
leading cause of infant mortality among American Indians.
Although infant mortality varied substantially by racial/ethnic
group, the rate of infant mortality due to birth defects was less
variable. Infant mortality rates due to birth defects were
highest among American Indians (2.9/1,000 live births), followed
by Asians and Hispanics (2.6) and blacks (2.5). In comparison,
white infant mortality due to birth defects was 2.3/1,000 live
The proportional mortality due to birth defects varied greatly by
racial/ethnic group. The proportional mortality was greatest
among Asians (27%) and Hispanics (24%), and less among American
Indians (18%) and blacks (13%). In comparison, proportional
mortality among whites was 25%.
Infant mortality rates were further analyzed by age at death.
Figure 3A shows infant mortality rates among infants who died in
the neonatal period ( less than 28 days of life). Again, although
mortality rates varied substantially by racial/ethnic group,
deaths due to birth defects were relatively constant (between 1.7
and 1.9 deaths/1,000 live births), regardless of racial/ethnic
group. Low birth weight, prematurity, and RDS combined
contributed the largest number of deaths during the neonatal
period, especially among black infants.
Although the risk of death from birth defects was stable across
racial/ethnic groups, the proportional mortality varied greatly.
During the neonatal period, proportional mortality was greatest
among Asians (32%), whites (30%), and Hispanics (27%) and lowest
among blacks (15%) and American Indians (25%).
Figure 3B shows mortality, by racial/ethnic group, in the
postneonatal period. The risk from birth defects remained
relatively constant (between 0.6/1,000 live births and 1.0/1,000
live births). The largest contributor to infant mortality during
the postneonatal period was SIDS; American Indians had the
highest rate, and blacks had the next highest rate. Proportional
mortality from birth defects remained relatively higher among
Asians (20%), whites (18%), and Hispanics (17%) than among
American Indians (12%) and blacks (11%).
Assessing infant mortality by age at death indicated that LBW,
prematurity, and RDS together contributed the largest number of
deaths in the neonatal period, whereas SIDS contributed the
largest number in the postneonatal period. However, birth defects
remained the overall leading cause of infant mortality, because
neonates infrequently died from SIDS and postneonates
infrequently died from LBW.
Figure 4 shows infant mortality rates by weight group ( less than
1,500 g, 1,500 g-2,499 g, and greater than or equal to 2,500 g).
Infants born weighing less than 1,500 g had a high rate of infant
mortality, with the risk of death in the first year being
approximately 400 deaths/1,000 live births for each of the
racial/ethnic groups. The importance of birth defects in this
group decreased compared with problems associated with
prematurity and LBW. However, a relatively constant risk of death
from birth defects remained. In all but the black group, the risk
of death attributed to birth defects was 30-40/1,000 live births,
accounting for approximately 7% of all mortality among these
Among infants born weighing between 1,500 and 2,499 g, birth
defects played a more important role. Asians had the highest rate
of infant deaths in this group at 16.1/1,000 live births, a rate
equivalent to that observed for white infants. American Indians
had a rate of 14.3/1,000 live births, followed by Hispanics at
13.7/1,000 live births. Blacks had the lowest rate at 8.5/1,000
Overall, proportional mortality was high in this weight group,
although it varied by racial/ethnic group. Proportional mortality
was highest among Asians (52%), followed by whites (44%),
Hispanics (39%), American Indians (31%), and blacks (29%).
Among infants born weighing greater than or equal to 2,500 g, the
risk of death from birth defects was highest among American
Indians at 2.0/1,000 live births, followed by Hispanics at
1.7/1,000 live births. The remaining racial/ethnic groups had
rates between 1.4 and 1.5/1,000 live births.
The proportional mortality was less in this group than in the
group weighing from 1,500 to 2,499 g: whites and Asians (32%),
Hispanics (31%), blacks (21%), and American Indians (20%).
Data on the underlying cause provided an incomplete picture of
the factors contributing to infant mortality. Because many
factors may have contributed to an infant's death, data supplying
multiple causes provided a better understanding of infant
mortality. The authors looked at birth defects that were listed
with other causes of death. Table 4 shows the number of records
with each of the 10 leading causes of death listed on the record.
The percentage of records with birth defects listed are also
shown. In the total population, 8,684 (25.1%) of all infant
deaths had at least one birth defect listed as a contributing
cause of death. Of the 13,068 infants with LBW or prematurity
listed as one of the causes of death, 986 (7.5%) had birth
defects also listed as a contributing cause. Infants with
hypoxia/asphyxia, unintentional injuries, pneumonia, and
perinatal infections had a relatively high proportion of birth
defects listed as well. A large proportion of infants with both
birth defects and unintentional injuries listed among the
multiple causes had injuries which were a result of medical or
Table 5 shows data on multiple cause by racial/ethnic group.
Asian infants had the largest proportion of infants with at least
one birth defect listed as a multiple cause of death, whereas
black infants had the smallest proportion. Substantial variation
in the contribution of birth defects existed between
racial/ethnic groups when looking at data on multiple causes. For
example, among records with unintentional injuries listed as a
multiple cause, the percentage of records with birth defects also
listed ranged from 12.9% among American Indians to 28.4% among
whites. On the other hand, among infants with perinatal
infections listed as a cause of death, American Indians had the
highest proportion of infants with birth defects also listed,
whereas black infants had the lowest proportion.
Overall, birth defects were the leading cause of infant
mortality. Among racial/ethnic minorities, birth defects were the
leading cause of infant mortality among Hispanics and Asians.
The risk of infant death from birth defects varied among
racial/ethnic groups, but for all ethnic groups, the risk was
higher than for white infants. American Indians had the highest
rates of lethal birth defects, followed by Asians, Hispanics, and
blacks. The variation in rate of lethal birth defects among
racial/ethnic groups may have been related to both incidence and
survival. In turn, variation in survival may have been related to
delivery and access to the health care system. These variations
among racial/ethnic minorities warrant further investigation.
The proportional mortality due to birth defects varied greatly by
racial/ethnic group predominately because of the increased
contribution of LBW, prematurity, and RDS among blacks and
because of SIDS among American Indians. The proportional
mortality due to birth defects was greatest among Asians,
followed by whites, Hispanics, American Indians, and blacks. In
addition, data on multiple causes indicated that birth defects
most often contributed to infant mortality among Asians, followed
by whites, Hispanics, American Indians, and blacks.
Because the proportional mortality due to birth defects varied
greatly among racial/ethnic groups, the substantial gap of infant
mortality that existed between minority and non-minority infants
will not be ameliorated by addressing birth defects alone. Black
and American Indian infants continued to have the highest rates
of overall infant mortality, which probably reflected differences
in access to medical care, socioeconomic status, nutrition, and
maternal lifestyles. These issues should be addressed in order to
close the gap represented by infant mortality rates.
Although black infants showed the highest overall rate of infant
mortality, American Indian infants actually had higher rates of
infant mortality when stratified by birth weight and postneonatal
period. This apparent discrepancy resulted from the higher
proportion of LBW infants among the black group than among the
American Indian group. Although 11.7% of black infants were born
weighing less than 2,500 g, only 5.5% of American Indians were
born weighing less than 2,500 g. The high rates of mortality
among LBW infants heavily influenced the overall mortality among
blacks as compared with American Indians.
Some analysts have attributed the rapid decline of infant
mortality rates in the 1970s to rising medical technology in the
care of premature and other critically ill newborns. In the
1980s, this decline in infant mortality rates slowed
considerably--partly because of a lack of progress in primary
prevention of conditions that lead to infant death. As a
consequence, the 1990 health objective of nine infant
deaths/1,000 live births is unlikely to be met (14).
Additionally, to meet the year 2000 objectives, health agencies
will have to make substantial efforts to prevent the leading
causes of infant mortality.
To decrease infant mortality due to birth defects,
population-based surveillance systems on birth defects must
continue to proliferate and expand in the United States and
throughout the world (15-17). Collaborative epidemiologic studies
are being done as part of the International Clearinghouse for
Birth Defects Monitoring Systems (18-20) and the European
Registry of Congenital Abnormalities and Twins (EUROCAT) project
(21,22). These surveillance systems have been invaluable
resources as population-based registries for evaluation of health
services and in the conduct of both descriptive epidemiologic
studies and follow-up studies. One example is the large-scale
case-control study conducted by the CDC between 1982 and 1984 to
test whether offspring of male Vietnam veterans were at greater
risk of having serious birth defects than offspring of men who
did not serve in Vietnam (23). Cases from the existing
Metropolitan Atlanta Congenital Defects Program (MACDP), which
began in 1968, were studied (24). Similarly, collaborative
efforts among state-based surveillance systems would improve the
ability to perform etiologic studies of birth defects. CDC has
increasingly focused efforts to standardize data-collection
instruments (on the basis of the MACDP system) in order to
facilitate this collaboration.
In summary, birth defects were an important contributor to infant
mortality among all racial/ethnic minorities. Epidemiologic data
obtained from surveillance systems and birth-defects registries
would provide the basis for the development of prevention
programs for infant mortality associated with birth defects among
racial/ethnic minorities. Specifically, surveillance systems on
birth defects should be used to evaluate whether racial/ethnic
differences in infant mortality from birth defects are due to
differences in incidence and/or survival among minority infants
with birth defects.
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