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ORIGINAL RESEARCH |
From the Departments of Pediatrics, Surgery, and Obstetrics and Gynecology, Pritzker School of Medicine, Chicago, Illinois; and the Irving B. Harris Graduate School of Public Policy Studies, University of Chicago, Chicago, Illinois.
Address reprint requests to: Kwang-sun Lee, MD, Department of Pediatrics, University of Chicago, MC 6060, Chicago Children’s Hospital, 5841 S. Maryland Avenue, Chicago, IL 60637; E-mail: klee{at}midway.uchicago.edu.
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ABSTRACT |
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METHODS: We used US annual summary data on cause-specific infant mortality for 1970–97 and detailed birth and infant death linked data for 1985–87, 1989–91, and 1995–97.
RESULTS: Congenital malformations became a more prominent cause of infant mortality in 1997 and accounted for 22.1% of all infant deaths compared with 15.1% in 1970. Congenital malformations of nervous, cardiovascular, and respiratory systems accounted for more than 60% of all malformation deaths. Malformations incompatible with life (anencephaly, encephalocele, hypoplastic lungs, renal agenesis, and trisomies 13 and 18) were the cause of one-third of all malformation deaths. In 1970–71, infant mortality caused by congenital malformations in nonwhites was lower, 2.6 (confidence interval [CI] 2.5, 2.7) per 1000, compared with whites, 3.1 (CI 3.0, 3.1) per 1000. However, in 1996–97, the rate of congenital malformation-specific infant mortality was higher in nonwhites, 1.7 (CI 1.7, 1.8) per 1000, compared with whites, 1.6 (CI 1.5, 1.6) per 1000. This trend was most pronounced with central nervous system malformations. Although whites had an almost two-fold higher infant mortality rate from central nervous system malformations compared with nonwhites in 1970–71, this disparity was no longer present by 1996–97.
CONCLUSION: Congenital malformations have become a leading cause of infant mortality in the 1990s. Over the last several decades, this mortality declined more slowly in nonwhites than in whites.
During recent decades, the infant mortality rate in the United States has declined from 20.0 per 1000 live births in 1970 to 7.1 per 1000 in 1997.1,2 Whereas the decline in infant mortality has been greatest for various perinatal disorders unrelated to congenital malformations, infant mortality caused by congenital malformations has proportionally been steadily increasing.1,2
Several regional studies have reported that trends in mortality from congenital malformations vary by subgroups of malformations and by maternal race.3–6 One earlier study7 of US birth cohorts showed a greater decline between 1960 and 1980 in the congenital malformation mortality risk for whites (from 3.6 per 1000 live births to 2.4) compared with blacks (from 2.9 per 1000 live births to 2.5). There has not been a report on a recent trend in mortality from congenital malformations in the US population examined by race and subgroups of malformations.
We examined the trend in infant mortality caused by congenital malformations in the entire United States for the period 1970–1997, to determine differences between whites and nonwhites and to determine mortality difference by malformation subgroups.
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MATERIALS AND METHODS |
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The second set was Birth Cohort Linked Birth and Infant Death Data of the United States for the years 1985–87 and 1989–91, and the Period Linked Birth and Infant Death Data File of the United States for the years 1995–97.15 The numerator of the Birth Cohort Linked Data sets consists of deaths to infants born in the specified year whether the death occurred in that year or the next. For example, the numerator for the period linked file for 1997 consists of all infant deaths occurring in 1997 linked to their corresponding birth certificates, whether the birth occurred in 1997 or 1996. The denominator file for this data set is the 1997 natality file. Using the second data set, the trend of infant mortality from individual specific malformations was further examined.
Differences in mortality rates between races and between the periods were compared using the z statistic for differences in proportions. Differences were considered statistically significant when the value of the z statistic was greater than or equal to 1.96.16
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RESULTS |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Over the last three decades, three organ systems, the nervous, cardiovascular, and respiratory systems accounted for more than 60% of all congenital malformation deaths (Table 1
). Between 1970 and 1997, the cardiovascular system contributed 59% of the total decline in malformation deaths, the nervous system, 35%, and the digestive system, 1%.
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). Compared with 1970–71, by 1996–97, there was a 66.6% reduction in the infant mortality for anencephaly, a 76.3% reduction for congenital hydrocephaly, and a 92.8% reduction for spina bifida. Among all specified cardiovascular malformation groups, hypoplastic left heart syndrome was the leading cause for infant deaths (Table 2). Other prominent causes were endocardial cushion defects (including other ventricular septal defects), transposition of the great vessels (including double outlet right ventricles), anomalies of the aorta, tetralogy of Fallot, and anomalies of the pulmonary artery. Although digestive system malformations accounted for a small proportion of all malformation deaths, mortality from malformations in this system showed the largest decline (84.2%).
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). The recent trend in infant deaths from chromosomal abnormalities is shown in Table 3. Autosomal trisomies were the most common causes for deaths from chromosomal abnormalities, accounting for more than 80% of all infant deaths in this group.
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The decline in infant mortality from congenital malformations varied by race (Figure 2). In 1970–71, infant mortality caused by congenital malformations in non-whites was lower, 2.6 (confidence interval [CI] 2.5, 2.7) per 1000, compared with whites, 3.1 (CI 3.0, 3.1) per 1000. However, from 1970–71 to 1996–97, the white rate declined 49.8% compared with 33.8% in nonwhites. By 1996–97, this rate was 11.0% higher in nonwhites, 1.7 (CI 1.7, 1.8) per 1000, compared with whites, 1.6 (CI 1.5, 1.6) per 1000 (P < .001). Racial disparity in this decline was greater in the early period 1970–71 to 1980–81 than the later period 1982–83 to 1996–97. In the early period, the rate for whites declined 10.4% compared with 1.9% in nonwhites, whereas in the later period, the rate for whites declined 35.7% compared with 30.6% in nonwhites and 29.3% in blacks.
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). Between 1970–71 and 1996–97, decline in this rate was far greater in whites, 72.9%, compared with 48.5% in non-whites. By 1996–97, there was no longer a significant difference in this mortality between whites and blacks (P > .05). For infant mortality caused by cardiovascular malformations, there was a more rapid decline among whites in the 1970s through the early 1980s, with the subsequent rate of decline similar for whites and non-whites (Figure 3B). The decline in infant mortality caused by digestive system malformations was similar for whites and nonwhites in the 1970–97 period. There was a rapid decline in this mortality in the 1970s, followed by a gradual slowing in the mortality reduction since the early 1980s (Figure 3C). Infant mortality from chromosomal disorders increased in both whites and blacks until the early 1990s, possibly explained by increasing detection of chromosomal abnormalities in the recent period. Since the early 1990s, this mortality has declined in both racial groups (Figure 3D).
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DISCUSSION |
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Obtaining a complete understanding of the trend in congenital malformations requires ascertainment of data in all pregnancy outcomes for a geographic population. Currently, with assistance from the Centers for Disease Control and Prevention, most states have established a birth defects surveillance system, but with varying degrees of ascertainment intensity.20 In the United States, there are two well-established birth defects surveillance systems. The National Birth Defects Monitoring Program ascertains birth defects using newborn discharge diagnoses from approximately 1200 midsized hospitals nationwide. The Metropolitan Atlanta Congenital Defects Program is a population-based surveillance system in the five counties that form metropolitan Atlanta. The National Center for Health Statistics has published birth and infant death data on US births, including causes of infant deaths. However, its report on fetal deaths lacks information on causes of death. In addition, entry of malformation data on the live birth certificate may not be completed within the requisite several days after birth. For these reasons, it is difficult to determine the true prevalence of all congenital malformations in the entire US population over recent periods. However, the trend of serious congenital malformations that invariably or often results in death may be reasonably ascertained using the linked birth and infant death certificate data.
The observed decline in infant deaths from congenital malformations among live-born infants may be attributable to several factors, including improved preventive measures for congenital malformations, increasing antenatal detection of serious malformations, selective termination of pregnancy, and the improved survival of infants with malformations. The progressive reduction in infant mortality from malformations incompatible with life (eg, anencephaly) reflects effective preventive measures and/or an increased antenatal detection and termination. Recent studies in developed countries have shown a decline in the number of live births with neural tube defects.21–28 Consumption of folic acid before conception and during early pregnancy has been shown to reduce the risk for neural tube defects.29,30 In 1992, the US Department of Health and Human Services recommended that all women of childbearing age who are capable of becoming pregnant should take 0.4 mg of folic acid per day.31 However, the observed progressive decline in neural tube defects occurred over the last three decades, and is therefore probably not attributed to an increase in folic acid intake among women of childbearing age. As shown in other countries20–23 and a regional population in the United States,26–28 the observed progressive decline in mortality among live-born infants from neural tube defects has more likely resulted from an increasing rate of antenatal detection and selective termination of the affected pregnancies.
In other groups of malformations including cardiovascular and gastrointestinal anomalies, notable advances have been made in the medical and surgical care of affected infants. An increasing number of infants with major cardiac or gastrointestinal defects can now survive. Our analysis of data from the last three decades shows that infant mortality from cardiovascular malformations was reduced by about one-half, and mortality from gastrointestinal malformations, to less than one-fifth of its previous level. This remarkable reduction in infant mortality particularly from cardiovascular malformations may not be entirely attributable to the improved survival of infants with these malformations, however. A regional referral center in England reported a striking fall in the number of newborn babies with hypoplastic left heart syndrome since the late 1980s.32 In this report, the investigators attributed the fall to an early and increasing detection of this malformation during routine obstetric ultrasound scanning and frequent selective termination of pregnancy with this malformation. A recent study in a tertiary center in Boston showed a significant increase in elective terminations of fetuses with a cardiovascular malformation from 0% to 22% during a recent 15-year period. In the same period, the proportion of liveborn infants with cardiovascular malformations decreased from 90% to 73% of the affected pregnancies.33
The birth prevalence of congenital malformations appears to vary by race.3–7 Previous studies have suggested that whites have a higher prevalence of major malformations and malformation-related deaths, as compared with blacks.34,35 However, this pattern appears to have changed over the recent three decades. In the 1990s, congenital malformation-specific infant mortality was higher in nonwhites (mostly blacks) than in whites, whereas it was lower in nonwhites than in whites in the 1970s. This trend was more pronounced in mortality from neural tube defects.
From our analysis, it is not possible to determine the reason(s) for this reversal in malformation-specific mortality rates of whites and nonwhites. The potential explanations include racial differences in 1) preventive measures (eg, folic acid intake), 2) access and use of antenatal screening and selective termination of pregnancy, and 3) medical and surgical interventions for infants with congenital malformations. The prevalence of antenatal testing for congenital malformations may vary with maternal race and educational status.36–38 Without access to or use of antenatal screening, there is no possible option for terminating pregnancy if the fetus has life-threatening congenital malformation. In a study36 of Georgia women aged 40 years and older, only 15% of pregnant women made use of prenatal chromosomal diagnosis. There was, however, substantial racial and geographic variation, ranging from a use ratio of 60% among whites in large urban counties to 0.5% among blacks residing in rural districts. Future studies should investigate the reasons for racial disparities in infant deaths caused by congenital malformations, including the impact of potential difference in access to and use of prenatal diagnostic and intervention services.
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Footnotes |
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Received January 30, 2001. Received in revised form May 17, 2001. Accepted June 7, 2001.
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REFERENCES |
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2. Hoyert DL, Kochanek KD, Murphy SL. Deaths: Final data for 1997. National Vital Statistics Reports, Vol. 47, No. 19. Hyattsville, MD: National Center for Health Statistics, 1999.
3. Malcoe LH, Shaw GM, Lammer EJ, Herman AA. The effect of congenital anomalies on mortality risk in white and black infants. Am J Public Health 1999;89:887–92.
4. Druschel C, Hughes JP, Olsen C. Mortality among infants with congenital malformations, New York State, 1983 to 1988. Public Health Rep 1996;111:359–65.[Medline]
5. Chavez GF, Cordero JF, Becerra JE. Leading major congenital malformations among minority groups in the United States, 1981–1986, CDC surveillance summaries. MMWR 1988;37:17–24.[Medline]
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7. Berry RJ, Buehler JW, Strauss LT, Hogue CJR, Smith JC. Birth weight-specific infant mortality due to congenital anomalies, 1960 and 1980. Public Health Rep 1987;102: 171–81.[Medline]
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9. Peters KD, Kochanek KD, Murphy SL. Deaths: Final data for 1996. National Vital Statistics Reports, Vol. 47, No. 9. Hyattsville, MD: National Center for Health Statistics, 1998.
10. Ventura SJ, Martin JA, Curtin SC, Mathews TJ. Report of final natality statistics, 1996. Monthly Vital Statistics Reports, Vol. 46, No. 11, Suppl. Hyattsville, MD: National Center for Health Statistics, 1998.
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18. Singh GK, Yu SM. Infant mortality in the United States: Trends, differentials, and projections, 1950 through 2010. Am J Pub Health 1995;85:957–64.
19. Petrini J, Damus K, Johnston RB. An overview of infant mortality and birth defects in the United States. Teratol 1997;56:8–9.
20. Erickson JD. Introduction: Birth defects surveillance in the United States. Teratol 1997;56:1–4.
21. Yen IH, Khoury MJ, Erickson JD, James LM, Waters GD, Berry RJ. The changing epidemiology of neural tube defects: United States, 1968–1989. Am J Dis Child 1992; 146:857–61.[Abstract]
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23. Cuckle H, Wald N. The impact of screening for open neural tube defects in England and Wales. Prenatal Diagnosis 1987;7:91–9.[Medline]
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
), and congenital hydrocephaly (
) in the United States, 1970–71 through 1996–97.
