Birth weight-specific causes of infant mortality, United States, 1980

To describe underlying causes of infant death by birth weight, we used data from the 1980 National Infant Mortality Surveillance project and aggregated International Classification of Diseases codes into seven categories: perinatal conditions, infections, congenital anomalies, injuries, sudden infant death syndrome (SIDS), other known causes, and nonspecific or unknown causes. Compared with heavier infants, infants with birth weights of 500-2,499 grams (g) are at increased risk of both neonatal and postneonatal death for virtually all causes. Sixty-two percent of neonatal deaths (under 28 days of life) were attributed to "conditions arising in the perinatal period," as defined using codes from the International Classification of Diseases. Prematurity-low birth weight and respiratory distress syndrome (RDS) were the leading causes of such deaths among infants with birth weights of 500-2,499 g, while birth trauma-hypoxia-asphyxia and other perinatal respiratory conditions were the leading causes among heavier infants. For all birth weight groups, congenital anomalies were the second leading cause, representing 27 percent of neonatal deaths. Although perinatal conditions caused nearly one-third of postneonatal deaths (28 days to under 1 year of life) among infants with birth weights of 500-1,499 g, for the other birth weight groups these conditions were much less important; predominant causes of postneonatal death were sudden infant death syndrome (SIDS), congenital anomalies, infections, and injuries. Black infants had a roughly twofold higher risk of neonatal and postneonatal death than did white infants for all causes except congenital anomalies, which occurred with almost equal frequency in blacks and whites. However, for infants with birth weights of 500-2,499 g, blacks had lower risks of neonatal death from RDS and congenital anomalies. Between 1960 (the latest year for which national birth weight-specific mortality statistics had been available) and 1980, SIDS emerged as a major diagnostic rubric. Otherwise, except for infections and congenital anomalies among infants with birth weights of 500-1,499 g, all causes of death declined in frequency among all birth weight groups.     

Overview of the National Infant Mortality Surveillance (NIMS) project--design, methods, results

The recent slowdown in the decline of infant mortality in the United States and the continued high risk of death among black infants (twice that of white infants) prompted a consortium of Public Health Service agencies to collaborate with all States in the development of a national data base from linked birth and infant death certificates. This National Infant Mortality Surveillance (NIMS) project for the 1980 U.S. birth cohort provides neonatal, postneonatal, and infant mortality risks for blacks, whites, and all races in 12 categories of birth weights. (Note: Neonatal mortality risk = number of deaths to infants less than 28 days of life per 1,000 live births; postneonatal mortality risk = number of deaths to infants 28 days to less than 1 year of life per 1,000 neonatal survivors; and infant mortality risk = number of deaths to infants less than 1 year of life per 1,000 live births.) Separate tabulations were requested for infants born in single and multiple deliveries. For single-delivery births, tabulations included birth weight, age at death, race of infant, and each of these characteristics: infant's live-birth order, sex, gestation, type of delivery, and cause of death; and mother's age, education, prenatal care history, and number of prior fetal losses at 20 weeks' or more gestation. An estimated 95 percent of eligible deaths were included in the NIMS tabulations. The analyses focus on three components of infant mortality: birth weight distribution of live births, neonatal mortality, and postneonatal mortality. The most important predictor for infant survival was birth weight, with an exponential improvement in survival by increasing birth weight to its optimum level. The nearly twofold higher risk of infant mortality among blacks was related to a higher prevalence of low birth weights and to higher mortality risks in the neonatal period for infants weighing 3,000 grams or more, and in the postneonatal period for all infants, regardless of birth weight. Regardless of other infant or maternal risk factors, the black-white gap persisted for infants weighing 2,500 grams or more.     

Regional differences in birth weight-specific infant mortality, United States, 1980

To describe regional differences in birth weight-specific infant mortality in the United States, we used data from the National Infant Mortality Surveillance project. The infant mortality risk (IMR) for the nation was 11.0 deaths per 1,000 live births. The risk (with 95 percent confidence intervals [CI]) for the four U.S. Census regions were West 9.9 (9.7 to 10.1), Northeast 10.4 (10.1 to 10.6), North Central 10.8 (10.6 to 11.0), and South 12.1 (11.9 to 12.3). In all regions, the IMR for blacks was approximately twice that of whites. Seventy-two percent of the higher IMR in the South was due to a higher proportion of black births compared with the remainder of the nation, reflecting the higher mortality rates suffered by black infants, and 28 percent to higher mortality among southern whites. The IMR for whites in the South was significantly higher than in the remainder of the nation: 9.8 versus 9.1 (relative risk = 1.09, CI = 1.06 to 1.11). Thirty-six percent of this excess in IMR was due to a higher frequency of low birth weight (less than 2,500 grams), 18 percent was due to higher IMR in infants with birth weight less than 2,500 grams, and 46 percent due to higher IMR in infants with birth weights of 2,500 g or more. Black infants born in the West had a lower risk of death than black infants in the other regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Overview of the National Infant Mortality Surveillance (NIMS) project

A slowdown in the decline of infant mortality in the United States and a continuing high risk of death among black infants (twice that of white infants) prompted a consortium of Public Health Service agencies, in collaboration with all states, to develop a national data base of linked birth and infant death certificates for the 1980 birth cohort. This project, referred to as National Infant Mortality Surveillance (NIMS), provides neonatal, postneonatal, and infant mortality risks for blacks, whites, and all races in 12 categories of birthweights. Tabulations were requested for infants born in single and multiple deliveries. For single-delivery births, tabulations included birthweight, age at death, race of infant, and each of these characteristics: infant's live-birth order, sex, gestation, type of delivery, and cause of death; and mother's age, education, prenatal care history, and number of prior fetal losses at greater than or equal to 20 weeks' gestation. An estimated 95% of eligible infant deaths were included in the NIMS tabulations. Analyses have focused on various components of infant mortality, including birthweight distribution of live births, neonatal mortality, and postneonatal mortality. The most important predictor for infant survival is birthweight; survival increases exponentially as birthweight increases to its optimal level. The nearly twofold higher risk of infant mortality among blacks than among whites was related to a higher prevalence of low birthweights, to higher mortality risks in the neonatal period for infants with birthweights of greater than or equal to 3,000 g, and to higher mortality during the postneonatal period for all infants, regardless of birthweight. Moreover, the black-white gap persisted for infants with birthweight of greater than or equal to 2,500 g, regardless of other infant or maternal risk factors.     

Variation in state-specific infant mortality risks

Data from the National Infant Mortality Surveillance project were used to examine the State-specific variations in infant, neonatal, and postneonatal mortality and to examine some of the factors affecting the risks of death. The infant mortality risk, defined as the risk of death before 1 year of age to an infant born in the 1980 birth cohort, in the highest risk State was nearly three times that in the lowest risk State. Mortality risk ratios of two or greater were found when comparing high and low States for overall black infant mortality risks, overall neonatal mortality, neonatal mortality risks for black and white infants examined separately, neonatal mortality risks for low birth weight infants regardless of race, and overall postneonatal mortality and postneonatal mortality for white infants. The lowest State-specific black mortality risks were higher than the highest white risks for overall infant mortality and neonatal mortality. The differences between State extremes in mortality risks are greater than the differences between the United States and the Scandinavian countries with the lowest infant mortality.     

Cause-Specific Trends in Neonatal Mortality Among Black and White Infants,United States, 1980–1995

Objective: Although neonatal mortality has been declining more rapidly than postneonatal mortality in recent decades, neonatal mortality continues to account for close to two-thirds of all infant deaths. This report uses U.S. vital statistics data to describe national trends in the major causes of neonatal mortality among black and white infants from 1980 to 1995. Methods: Mortality rates were estimated as the number of deaths due to each cause (based on International Classification of Diseases, 9th Revision, codes) divided by the number of live births during the same time period. Linear regression models and smoothed rates were used to describe trends. Results: During the study period, neonatal mortality declined 4.0% per year for white infants and 2.2% per year for black infants, and the black–white gap increased from 2.0 to 2.4. By 1995, disorders relating to short gestation and low birth weight were the number one cause of neonatal death for black infants and the number two cause for white infants, had the highest black–white disparity (4.6, up from 3.3 in 1980), and accounted for almost 40% of excess deaths to black infants (up from 24% in 1980). Congenital anomalies were the number two cause of neonatal death for black infants and the highest ranked cause for white infants in 1995, and it is the only cause for which there was not a substantial excess risk to black infants. Conclusions: Large declines in neonatal mortality have been achieved in recent years, but not in the black–white gap, which has increased. Declines were slower for black than white infants overall and for almost all causes. Prevention of preterm delivery and low birth weight continue to be a priority for reducing neonatal mortality, particularly among black infants. Although congenital anomalies do not contribute substantially to the black–white gap, their diagnosis, treatment, and prevention is critical to reducing overall neonatal mortality.     

U.S. differentials in infant mortality: why do they persist?

Large racial differentials in infant mortality persist in the US. While black babies made up 3.54 million singleton deliveries in the US in 1980, they accounted for 35% of all low-birthweight infants nationwide. Because of this disadvantage in birthweight, black babies accounted for 28% of infant deaths. Furthermore, while overall risk of infant mortality declined from 23.3/1000 live births to 11/1000 from 1960 to 1980 due to technological advances, the gap in infant mortality between black and white babies remains. The chances that a black infant wil die during the 1st year of life are still 2 times greater than white infants--the same odds as existed in 1960. Investigators concluded that the higher proportion of low birth weight babies among blacks is due to adverse socioeconomic conditions. Other recent studies cited in Arizona, Ohio, and California expand on this theory, suggesting that cultural, social, and biological factors may interact to create unique mortality patterns among racial and ethnic subgroups. The number of and risk for infant deaths is given for sex of infant, birth order, mother's age and region of birth.     

Comparison of infant mortality among twins and singletons: United States 1960 and 1983

Infant mortality among US black and white twins and singletons was compared for 1960 and 1983 using the Linked Birth/Infant Death Data Sets from the National Center for Health Statistics. Both twin and singleton infant mortality rates showed impressive declines since 1960 but almost all of the improvement in survival for both twins and singletons was related to increased birth weight-specific survival rather than improved birth weight distribution. One-half of white twins and two-thirds of black twins weighed less than 2,500 g at birth, and 9% of white twin births and 16% of black twin births were in the very low (less than 1,500g) birth weight category. In 1983, twin infant mortality rates were still four to five times that of singletons. However, twins had a survival advantage in the 1,250-3,000 g range, which persisted after adjustment for gestational age. Cause-specific mortality among twins was considerably higher for every major cause of death: twin mortality risks due to newborn respiratory disease, maternal causes, neonatal hemorrhage, and short gestation/low birth weight were six to 15 times that of singletons. The lowest twin-to-singleton mortality ratios observed were for congenital anomalies and sudden infant death syndrome with relative risks twice that of singletons. The data underscore the need to develop effective strategies to decrease infant mortality among twins.     

Previous fetal loss and risk of sudden infant death syndrome in subsequent offspring.

The relationships between previous fetal loss (obtained by mother's statement) and certain categories of infant death including probable instances of the sudden infant death syndrome (SIDSp) were examined. The deaths were those occurring among the cohort of live singleton births born in the State of North Carolina, 1960-1967. SIDSp were defined by age (28-364 days), place of death (outside the hospital), and certain ICD code numbers of the 7th Revision (273, 331, 422.2, 491-493, 500-501, 522, 525, 527.2, 762, 795 and 924). Other deaths in the postneonatal period were dichotomized between congenital malformations (ICD 750-759) and all other causes combined. Neonatal deaths were classified as due to either congenital malformations or other causes. For neonatal deaths and for all categories of deaths other than SIDSp in the postneonatal period there was a strong tendency for the standardized mortality ratios (SMR) to increase with increasing history of previous fetal loss. This was true for blacks and whites, and for both mothers under and over 25 years of age. The SMR for SIDSp, on the other hand, suggested an opposite association among blacks and little association among whites. Overall there was a significant difference between the patterns for SIDSp and all other postneonatal causes of death combined.     

Variations in pregnancy outcomes by race among 10-14-year-old mothers in the United States.

This study used the 1983-86 U.S. Linked Live Birth-Infant Death Files to examine variations in pregnancy outcomes among 38,551 U.S. resident black and white adolescents ages 10 through 14. The birth rate was 4.29 per 1,000 for blacks, more than 7 times the rate for whites (.59 per 1,000). Black mothers had higher proportions of very low and low birth weight infants than did whites (very low birth weight: 3.7 versus 2.6; low birth weight: 15.0 versus 10.5). Neonatal and infant mortality rates were higher among very low birth weight and low birth weight white infants. Neonatal and infant mortality rates were similar for normal birth weight infants of both races, but were 3.7 to 7.4 times higher among black infants with birth weights more than 4,250 grams. Logistic regression indicated that black mothers were at higher risk for having infants who were low birth weight, very low birth weight, small for gestational age, preterm, and very preterm. There were no differences by race for neonatal, postneonatal, and infant mortality. While the risk for poor pregnancy outcomes is great among young adolescents, young black adolescents appear to be particularly vulnerable. Attempts to reduce unintended pregnancies in this group should receive highest priority.     

Impact of very low birthweight on the black-white infant mortality gap.

In recent years, the rate of decline for the black infant mortality risk (IMR) has been slower than that for whites. The resultant widening in the black-white infant mortality gap has been accompanied by an increased percentage of very low birthweight (VLBW) infants (227 g-1,499 g) among black live births. Restricting our analysis to non-Hispanic black and white single live births, we used the 1983 national linked birth-death file to assess the relative contribution of VLBW infants to the black-white gap in IMR. VLBW occurred among 2.3% of all black live births and among 0.8% of all white live births. Deaths among VLBW infants accounted for 62.5% of the black-white gap in IMR. Although VLBW newborns represent a fraction of all live births in the United States, they account for almost two-thirds of the black-white gap in IMR. Since preterm delivery is associated with most VLBW infant deaths, our findings indicate the crucial need to identify strategies that reduce preterm births, among blacks in particular, to reduce significantly the infant mortality gap in the United States.     

Young maternal age and infant mortality: the role of low birth weight

In 1980, there were 562,330 babies born in the United States to teenage mothers (19 years of age or younger). The offspring of teenage mothers have long been known to be at increased risk of infant mortality, largely because of their high prevalence of low birth weight (less than 2,500 grams). We used data from the National Infant Mortality Surveillance (NIMS) project to examine the effect of young maternal age and low birth weight on infant mortality among infants born in 1980 to U.S. residents. This analysis was restricted to single-delivery babies who were either black or white, who were born to mothers ages 10-29 years, and who were born in one of 48 States or the District of Columbia. Included were 2,527,813 births and 28,499 deaths (data from Maine and Texas were excluded for technical reasons). Direct standardization was used to calculate the relative risks, adjusted for birth weight, of neonatal mortality (less than 28 days of life) and postneonatal mortality (28 days to less than 1 year of life) by race and maternal age. There was a strong association between young maternal age and high infant mortality and between young maternal age and a high prevalence of low birth weight. Neonatal mortality declined steadily with increasing maternal age. After adjusting for birth weight, the race-specific relative risks for babies born to mothers less than 16 years of age were still elevated from 11 to 40 percent, compared with babies born to mothers 25-29 years of age.(ABSTRACT TRUNCATED AT 250 WORDS)     

Surveillance of postneonatal mortality, United States, 1980-1987

In the United States, one-third of all infant deaths (deaths of infants ages 0-364 days) occurs in the postneonatal period (28-364 days). A substantial proportion of these deaths potentially could be prevented. To examine recent trends in postneonatal mortality (PNM) in the United States, the investigators analyzed birth and death certificate data for resident infants for the period from 1980 through 1987. Rates of PNM declined 11% from 3.5 to 3.1/1,000 live births among white infants and declined 16% from 7.3 to 6.1/1,000 live births among black infants. Most of the decline resulted from reduced mortality from infectious diseases and injuries. A decreased mortality attributable to sudden infant death syndrome (SIDS) among black infants additionally accounted for the decline. Autopsy rates for SIDS increased from 82% to 92% but did not differ for black infants and white infants. Birth defects-related PNM declined more among white infants than among black infants. The racial gap in PNM (rate ratio (RR) = approximately 2.0) persisted. However, the largest black/white gap occurred in the Northeast (RR = 2.5), the region with the lowest PNM. Black infants were 2.7 and 2.3 times more likely to die of infections and injuries, respectively, than were white infants. Although PNM rates declined during the 1980s, a greater rate of reduction is needed to achieve the Year 2000 objectives, especially among black infants. Such reductions are possible through improved access to comprehensive pediatric care as well as education and community-oriented prevention programs designed to reduce deaths due to infections and injuries. A better understanding of the etiology of SIDS and birth defects is critical for preventing postneonatal deaths.     

The association of maternal smoking with age and cause of infant death

Linked birth certificate and infant death certificate data from Missouri for 1979-1983 were used to explore the association of maternal smoking with age and cause of infant death. The data included 305,730 singleton white livebirths, of which 2,720 resulted in infant deaths. Using multiple logistic regression to control for the confounding effects of maternal age, parity, marital status, and education, the authors found that smoking was associated with both neonatal and post-neonatal mortality and with each cause of death except congenital anomalies. The adjusted odds ratio for smoking was higher for postneonatal deaths than neonatal deaths and was particularly high for two causes: respiratory disease (odds ratio = 3.4) and sudden infant death syndrome (odds ratio = 1.9). A moderate odds ratio (about 1.4) was found for causes attributed to the International Classification of Diseases, 9th Revision Perinatal Conditions Chapter. Although the associations for neonatal deaths and perinatal conditions were partially attributable to the effect of maternal smoking in lowering birth weight, virtually none of the excess respiratory mortality and sudden infant death syndrome mortality among the offspring of smokers was attributable to birth weight differences between the infants of smokers and nonsmokers. This suggests that respiratory deaths and sudden infant death syndrome deaths may be related to the effect of passive exposure of the infant to smoke after birth.     

Birthweight-specific infant mortality risk in cesarean section.

The role of cesarean section in improving infant survival has not been clearly documented. We calculated birthweight- and race-specific infant, neonatal, and postneonatal mortality risks by method of delivery for single- and multiple-delivery infants, using data from 14 states, reported to the Centers for Disease Control through the 1980 National Infant Mortality Surveillance project. For single-delivery infants, the risk of death for infants delivered by cesarean section was 1.6 times higher than for infants delivered vaginally among blacks and 1.2 times higher among whites. The risk was 1.7 times higher during the neonatal period and 1.2 times higher during the postneonatal period. For infants with birthweight less than 1,000 grams, the risk of death was lower when infants were delivered by cesarean section. The risk of death among multiple-delivery infants born by cesarean section was significantly lower than for those born vaginally. This analysis demonstrates that, unlike other birthweight categories, infants with a very low birthweight may have better outcomes if delivered by cesarean section. However, we cannot recommend the routine use of cesarean section for delivering very low birthweight infants. Further studies are needed to determine survival of such infants after controlling for maternal and infant conditions that prompted delivery by cesarean section.     

Congenital malformations as a cause of neonatal and postnatal death in Massachusetts (1970-1980)

Massachusetts birth and death certificate tapes for the years 1970-1980 were linked and analyzed to determine causes of death in the neonatal and postneonatal periods and to identify any related sociodemographic factors. Our analysis suggests that, although the neonatal mortality rate declined by about 43 percent, the postneonatal mortality rate remained relatively unchanged. Perinatal problems remained the principal cause of death during the neonatal period, throughout the decade. In the postneonatal period, congenital malformations became a leading cause of death toward the end of the decade because of a reduction in mortality from infectious diseases and perinatal problems. Infants born to mothers under 18 and over 34 years of age had the highest death rates from congenital birth defects. Higher mortality rates caused by congenital malformations were found in the more industrialized areas of Massachusetts. Further declines in infant mortality rates in Massachusetts will depend on preventive measures to reduce the incidence of congenital malformations.     

A characteristic change in infant mortality rate decrease in Japan

Changes in infant mortality rate (IM) in Japan were observed over a 41-year period, since the end of the Second World War (1947-1987). Both neonatal mortality rate (NM) and infant mortality rate excluding neonatal deaths (IEN) were measured. It was observed that IM had considerably decreased during the observation period. A decrease of IEN contributed greatly to this fall till the 1960s and less so since the 1970s. The slope of the decrease of NM became steeper after entering the 1980s compared with that of IEN, and this contributed to the decrease of IM in this period. In order to analyse this phenomenon, detailed observations were made of the causes of death. On studying three of the major causes of infant deaths in Japan (congenital anomalies, birth trauma and perinatal asphyxia, and injuries and poisoning) it was found that there was only a small annual difference in the number of deaths due to congenital anomalies compared with the much greater difference seen with the other two causes; therefore, improvement of mortality rate by congenital anomalies seemed difficult because the efficacy of improvement of medical treatment and care are already approaching their limits. For a further reduction of IM in the future, improvement of perinatal care and prevention of injuries are considered to be essential.     

"Development" is not essential to reduce infant mortality rate in India: experience from the Ballabgarh project

BACKGROUND: India aims to reduce the infant mortality rate (IMR) to below 60 per 1000 live births by 2000. IMR is higher in northern India as compared with south Indian states like Kerala. Any further reduction in IMR needs identification of new strategies. The Ballabgarh project with an IMR of 36 in 1997 can help identify such strategies. OBJECTIVE: To see the trend in reduction of neonatal mortality rate (NNMR) and IMR at the Ballabgarh project, compare it with Kerala and rural India's trend and look at the causes of neonatal and infant mortality. DESIGN: The Comprehensive Rural Health Services Project, Ballabgarh, run by the All India Institute of Medical Sciences, covered an estimated population of 70,079 in 1997. The health care delivery system is on the national pattern. All the deaths are identified during the house visits by the male workers. The cause of death is ascertained by the health assistant based on the symptomatology at the time of death. RESULTS: The trends in reduction of IMR for Ballabgarh, Kerala and rural India are roughly parallel with the IMR of Ballabgarh lying somewhere in between the two. However, the NNMR of Ballabgarh (10.6 in 1996) was comparable to Kerala's NNMR (10.9 in 1992). The proportion of infant deaths occurring during the neonatal period had fallen from 50% in the early seventies to 30% during 1996-97. In 1992-1994, 33.8% of all neonatal deaths were attributable to low birth weight and 37.3% to infective causes. Acute respiratory infection and diarrhoea continue to be the chief cause of postneonatal mortality. CONCLUSION: It is possible to bring down neonatal mortality before postneonatal mortality. The Kerala model, which focuses on social development, may not apply to northern India for sociocultural reasons.     

Importance of the first day death rate in infant mortality

The conventional partition of infant mortality into neonatal and postneonatal deaths, with the 28th day postpartum as the dividing line, has lost much of its epidemiological rationale in countries with low infant death rates. Infant deaths are concentrated increasingly at the start of the neonatal period: one out of three infant deaths in the United States occurs during the first 24 hours. Circumstances of early neonatal deaths differ considerably from those of later neonatal deaths. Failure to monitor separately early and late neonatal mortality can compromise the recognition of distinct epidemiological patterns. Racial disparities in the US tend to be larger for first day deaths than for any other infant deaths. Total US infant mortality declined rapidly in the 1950s and 1960s but first day deaths rose at a steady pace. Surveillance of infant mortality, whether on the national or the community level, should encompass first day, first month and first year death rates.