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.     

Method of Delivery and Neonatal Mortality among Very Low Birth Weight Infants in the United States

OBJECTIVE: To examine the association between method of delivery (primary cesarean section vs. vaginal) and neonatal mortality risk (as well as causes of death) among very low-birth weight first-born infants in the United States. More specifically, to examine this association separately for breech/malpresenting and vertex-presenting infants, while adjusting for selected maternal characteristics, and pregnancy, labor and delivery complications. METHODS: The study population was derived from the 1995-1998 birth cohort linked birth/infant death data sets. Binary and multinomial logit regression analyses were performed to assess the relationship in four very low-birth weight categories. RESULTS: Among breech/malpresenting neonates, compared to those delivered vaginally, infants delivered by a primary cesarean section had significantly lower adjusted relative risks of death for all very low-birth weight categories and the decrease in relative risk tended to be larger with each increasing birth weight category. However, for vertex-presenting neonates, results are mixed, suggesting decreased relative mortality risks associated with primary cesarean section, which were significant for 500-749 g, not significant for 750-999 g, and barely significant for 1,000-1,249 g. In contrast, for vertex-presenting neonates weighing 1,250-1,499 g, there was a significantly increased adjusted relative risk associated with primary cesarean section. Differences in cause-specific neonatal mortality by method of delivery and presentation status were also discussed. CONCLUSIONS: Primary cesarean section appears to be associated with decreased neonatal mortality risks in each very low-birth weight category for breech/malpresenting infants, but results are mixed for vertex-presenting infants. Causal inferences should be avoided because this was an observational study by design.     

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.     

Evaluating the risks of cesarean section: low Apgar score in repeat C-section and vaginal deliveries.

Data from Washington State birth certificates from 1980-83 were used to estimate excess risk to the infant delivered via repeat cesarean section independently of any risk associated with the indication for the procedure. Using a case-control design, we compared the method of delivery of all infants with low (0-6) five-minute Apgar scores born to multiparous mothers after uncomplicated pregnancies and births to that of similar infants with a high score (7-10), frequency matched by birthweight. Of the 1,030 infants with low Apgar score, 127 (12.3 per cent) were delivered via repeat cesarean section, in contrast to 98 (9.8 per cent) of 998 controls with high Apgar score. In a regression model controlling for birthweight, gestational length, maternal age, and income the relative risk was 1.29 (95% confidence interval 0.97, 1.72). Excess risk was highest among babies of normal (2500-4000 grams) birthweight. While a number of limitations inherent in the source of data require cautious interpretation of these results, we conclude that some excess risk of low Apgar score may be associated with repeat cesarean section procedures.     

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.     

Midwifery care, social and medical risk factors, and birth outcomes in the USA

STUDY OBJECTIVE: To determine if there are significant differences in birth outcomes and survival for infants delivered by certified nurse midwives compared with those delivered by physicians, and whether these differences, if they exist, remain after controlling for sociodemographic and medical risk factors. DESIGN: Logistic regression models were used to examine differences between certified nurse midwife and physician delivered births in infant, neonatal, and postneonatal mortality, and risk of low birthweight after controlling for a variety of social and medical risk factors. Ordinary least squares regression models were used to examine differences in mean birthweight after controlling for the same risk factors. STUDY SETTING: United States. PATIENTS: The study included all singleton, vaginal births at 35-43 weeks gestation delivered either by physicians or certified nurse midwives in the United States in 1991. MAIN RESULTS: After controlling for social and medical risk factors, the risk of experiencing an infant death was 19% lower for certified nurse midwife attended than for physician attended births, the risk of neonatal mortality was 33% lower, and the risk of delivering a low birthweight infant 31% lower. Mean birthweight was 37 grams heavier for the certified nurse midwife attended than for physician attended births. CONCLUSIONS: National data support the findings of previous local studies that certified nurse midwives have excellent birth outcomes. These findings are discussed in light of differences between certified nurse midwives and physicians in prenatal care and labour and delivery care practices. Certified nurse midwives provide a safe and viable alternative to maternity care in the United States, particularly for low to moderate risk women.     

Delivery type and neonatal mortality among 10,749 breeches.

Data on 10,749 breech presentations were analyzed for the effect of delivery type on neonatal mortality. Most of the data are from developing countries, and most of the hospitals have higher mortality than is found in Europe or the United States. The simultaneous effect of type of hospital where the delivery occurred, type of breech, birthweight, and parity were examined. The benefit of cesarean delivery was greater for nulliparae than multiparae, greater for footlings than for frank or complete breeches, and greater for larger babies than smaller ones. This last finding probably reflects the quality of neonatal care in developing country hospitals rather than the value of cesarean section. Maternal mortality and morbidity was higher among women delivered abdominally than among those delivered vaginally.     

The epidemiology of perinatal mortality in multiple births.

The epidemiology of perinatal mortality in multiple pregnancies was investigated from data on 16,831 multiple births from New York City''s computerized vital records for 1978-1984. Twins had a sixfold higher rate of neonatal death and a threefold higher rate of fetal death during labor than had singleton infants. Much of this excess mortality can be explained by the lower birthweight distribution in twins: between 1,001 and 2,500 grams twins had birthweight-specific death rates equivalent to or substantially less than singletons. However, in infants of normal birthweights, twins had more than three times the mortality risk of singletons. For twins in vertex presentation between 1,001 and 3,000 grams, cesarean section did not appreciably reduce neonatal mortality risk. For twins in vertex presentation who weighted more than 3,000 grams the neonatal mortality rate was more than four times higher in vaginal deliveries than in cesarean sections (exact p = 0.034). Efforts to prevent intrapartum and neonatal mortality in multiple births should aim at reducing the incidence of low birthweight twins. More research is needed on the etiology of perinatal problems in normal birthweight twins (greater than or equal to 2,501 grams), especially on the effects of different modes of delivery.     

Neonatal diarrhea at a maternity hospital in Rangoon.

Between 1981 and 1986, 1,540 infants born at the Central Women's Hospital in Rangoon were transferred to the Sick Baby Unit because of diarrhea (15.4 per 1,000 live births). Rates among cesarean infants were five times as high as those of infants born vaginally (51.0 and 10.3 per 1000 live births, respectively). One hundred eighty-four of the infants with diarrhea died (case fatality rate = 12 percent). We conclude that neonatal diarrhea is endemic in this large maternity hospital in Burma, and that control efforts should be targeted especially to cesarean and low birthweight infants.     

Birthweight-specific infant mortality for native Americans compared with whites, six states, 1980.

We used data from the National Infant Mortality Surveillance (NIMS) project to compare birthweights and birthweight-specific mortality risks among Native American and White infants. Because race categories in NIMS were limited to White, Black, and all, we studied six states in which greater than 85 per cent of newborns who were neither White nor Black were Native American. In these states, the infant mortality risk (IMR) among Native Americans was 15.3 deaths per 1,000 live births compared with 8.7 deaths among Whites, relative risk (RR) = 1.8 (95% CI = 1.5-2.0). The percentage of Native American infants with less than 2,500 g birthweights was 5.8 per cent versus 5.0 per cent for White infants. Birthweight-specific neonatal mortality risks were similar for the two race groups, but birthweight-specific postneonatal mortality risks (PNMRs) were more than three times as high among Native Americans compared with Whites for infants of greater than or equal to 2,500 g birthweight. PNMRs were elevated for most causes of death and for all categories for maternal age, educational attainment, trimester prenatal care began, and number of previous live births. Leading causes of postneonatal death among Native Americans of greater than or equal to 2,500 g birthweight were sudden infant death syndrome and infections.     

A population-based registry study of infant mortality in the Arctic: Greenland and Denmark, 1973-1997

OBJECTIVES: We sought to determine precise estimates of infant mortality rates and to describe overall trends in infant mortality in Greenland and Denmark from 1973 to 1997. METHODS: We analyzed data from population-based registries of all live-born infants in Greenland and Denmark to calculate infant mortality rates from 1973 to 1997. RESULTS: Between the periods of 1973-1977 and 1993-1997, neonatal mortality rates in Greenland declined from 20.9 per 1000 live-born infants to 15.7, and postneonatal mortality rates declined from 20.9 per 1000 to 5.9. Infant mortality rates were significantly higher in Greenland than in Denmark, and the excess mortality was uniformly distributed over all birthweight percentiles. In Greenland, the risk of infant death was significantly lower if the mother was born outside Greenland. CONCLUSIONS: Postneonatal mortality rates in Greenland have decreased significantly during the past 25 years, but little progress has been made in decreasing neonatal mortality rates. Disparities exist among children with different maternal origins.     

Differences in trends of postneonatal mortality by birthweight in upstate New York, 1968-1979.

Postneonatal mortality among neonatal survivors and the distribution of age at death among infant deaths were examined for births occurring in upstate New York, 1968-1979. Postneonatal mortality rates increased among infants weighing 501-1500 grams. Infants weighing 1501-2000 grams experienced an increase in postneonatal mortality during the mid-1970s, later returning to the level of 1968. Among infants 2001+ grams, postneonatal mortality declined throughout the study period. Among all levels of birthweight, the proportion of infant deaths occurring as postneonatal deaths increased.     

Time of birth and risk of intrapartum and early neonatal death

BACKGROUND: Previous studies have found that infants born at night and during weekends and holidays have an increased risk of perinatal mortality. However, these associations may be confounded by the distribution of high-risk deliveries according to time of birth. METHODS: We undertook a population-based cohort study of 694,888 singleton births without elective cesarean section in Sweden between 1991 and 1997. We estimated relative risks of intrapartum and early neonatal death according to the hour, day and month of delivery. Estimated risk ratios were adjusted for gestational age, birth weight for gestational age, malformations, induction of labor, breech presentations and year of birth. RESULTS: Infants of high-risk deliveries were more often delivered during daytime (8:00 am to 7:59 pm). Compared with infants born during daytime, infants born at night were at increased risk of early neonatal death (adjusted risk ratio = 1.28; 95% confidence interval = 1.13-1.46), but not intrapartum death (1.05; 0.71-1.54). If this association is causal, 12% of early neonatal deaths can be attributed to the increased risk among nighttime births. There was no association of weekend or holiday births with risks of intrapartum or early neonatal death. CONCLUSIONS: Infants born at night may be at increased risk of early neonatal death.     

Mortality risk of small infants varies with their mother's birthweight and race

We analysed a transgenerational linked birth file to investigate the relationship between maternal birthweight and infant birthweight-specific mortality risk for white and African American infants. Birth records of 267,303 infants born between 1989 and 1991 were linked to records of their mothers, born between 1956 and 1976, and to their own death certificates for those dying in the first year. The means, standard deviations and z-scores were calculated for each race- and generation-specific birthweight distribution. Investigators then analysed the mortality of very small infants (birthweight at least two standard deviations below their mean) for three maternal birthweight categories. Over half of the infant deaths involved births with weights more than two standard deviations below the relevant population mean birthweight (comprising 4.2% of white and 6.9% of African American births respectively). African American infants experienced higher mortality rates at all levels of standardised birthweight, from z-scores of -3 to +3. The relative risk of mortality associated with very small infant size was less for infants delivered to smaller birthweight mothers when compared with those whose mothers were average sized or large at birth. This differential effect was confined to neonatal deaths and was more prominent in the white subpopulation.     

Psychosocial sequelae of cesarean delivery: review and analysis of their causes and implications

A growing number of children around the world are being born by surgical delivery, or cesarean section. Concerns over rising rates of cesareans have focused on the risk of death and medical complications associated with surgical delivery but have largely neglected psychosocial and behavioral factors that affect and are affected by cesarean delivery. We summarize research which indicates that women who deliver by cesarean section have more negative perceptions of their birth experience, their selves, and their infants, exhibit poorer parenting behaviors, and may be at higher risk for postpartum mood disturbance compared to women delivering infants vaginally. We also review evidence that suggests that cesareans adversely influence women's moods and perceptions by restricting the control that they can exercise over birth and by violating expectations about childbirth. Based on these findings, we recommend ways to reduce the aversiveness of cesareans, offer recommendations for future research, and discuss implications of escalating rates of cesareans, including medically non-indicated cesareans by request.     

Geographic Accessibility to Health Services and Neonatal Mortality Among Very-Low Birthweight Infants in South Carolina

Introduction Mortality for infants born with very-low birthweight (VLBW, 500–1499 grams) is markedly higher than for babies born with normal birthweight (2500–4000 grams). Although these high-risk infants show better outcomes in advanced care settings, only 80 % of VLBW infants born in South Carolina (SC) are delivered in hospitals with a level-III neonatal intensive care unit (NICU). The purpose of this research project was to assess geographic access to delivery hospitals and risk of neonatal death among singleton VLBW infants born in SC. Methods The linked birth and death records of a cross-sectional, population-based study of singleton VLBW infants born in SC between 2010 and 2012 were used (n = 2030). We assessed the impact of travel time from maternal residence to delivery hospital. Logistic regression modeling was performed with adjustments for maternal, newborn, and hospital characteristics. Results The neonatal mortality rate among singleton VLBW infants was 11.03 deaths per 100 live births in 2010–2012. We did not find a significant association between travel time to delivery hospital and neonatal mortality after adjusting for confounders. However, we found that a 1-week increase in gestational age (odds ratio (OR): 0.61) and non-Hispanic black mothers (versus non-Hispanic white mothers) (OR: 0.68) were associated with lower odds of neonatal death, whereas non-NICU admission at birth (OR: 5.90) was associated with increased odds of death. The results of the sensitivity analyses including both singleton and multiple births did not yield significant results for travel time and neonatal mortality in VLBW infants. Discussion Although we found no significant association between travel time and neonatal mortality in singleton VLBW births in SC, we identified significant factors consistent with those found in previous studies that may affect neonatal mortality.     

新生儿2 694例出生情况分析

【目的】 了解本院目前新生儿出生状况及与全国新生儿出生情况的差别。 【方法】 统计2010年5月1日0时-2011年4月30日24时山东大学齐鲁医院产科出生的所有新生儿,采用中国新生儿协作网对其出生情况进行回顾性分析。 【结果】 1)齐鲁医院早产儿的发生率为13.96%,死亡率为47.87‰,均高于国家水平,死亡新生儿均为早产儿;2)对早产的高危因素进行分析,前三位为妊高症、双胎/多胎、胎膜早破;3)新生儿出生性别比为110;4)占住院新生儿前三位为早产(36.13%)、高胆红素血症(25.21%)、肺炎(10.92%);5)本院分娩剖宫产率为56.20%,其中选择性剖宫产占79.60%;6)新生儿窒息发生率为4.38%。 【结论】 应加强孕前教育及产前保健检查,严格掌握剖宫产指征,提高其成活率及生存质量。     

Risk factors for infant mortality from diseases in Japan 1995-98

OBJECTIVE: Since 1995, additional information (i.e. birth weight, singleton/multiple births, gestational weeks, maternal age, maternal parity and stillbirth experience) has been required for certificates of infant (less than 1 year of age) death from diseases in Japan. The present study examined the effects of biological, demographic and social variables, as reported on birth and death certificates, on infant, neonatal and postneonatal mortality in Japan. METHODS: Using data from vital statistics between 1995 and 1998, more than 4,787,000 livebirths and 16,000 infant deaths from diseases were analyzed. Univariate and multivariate analyses with the Poisson regression model were employed to assess the effects of variables on infant, neonatal and postneonatal mortality by singleton and multiple livebirths separately. RESULTS: The infant mortality rates from diseases were 3.2/1000 for singleton livebirths and 17.7/1000 for multiple livebirths. In singleton livebirths, low birth weight, infant born in earlier years, being a male infant, employment status as "unemployed or unknown", short gestational weeks, late birth in multiparity and maternal stillbirth experience were all significantly related to increased risk of neonatal and postneonatal deaths. Teenage mother were also at high risk of postneonatal deaths. Regional differences were observed. Compared with singleton livebirths, birthweight-specific mortality rates in multiple livebirths were relatively low among infants weighing under 2500 g. In multiple livebirths, elevated risk of death was associated with low birth weight, infant born in earlier years, employment status as "unemployed or unknown" and short gestational weeks. However, late birth in multiparity was related to a reduced risk of death, and maternal stillbirth experience was not a significant variable. CONCLUSION: This study provided the first quantitative estimate of risk of infant mortality from diseases in Japan. Since a more detailed elucidation of actual conditions and risk factors of infant deaths by vital statistics has become possible, efficient measures for improvement of infant mortality are to be expected.     

Maternity and infant care, race and birth outcomes

We examine the effect of a large, comprehensive maternity and infant care (MIC) program on birthweight and infant mortality in an economically depressed urban population. The study is based on linked birth, infant death and program files for 1985-87 Cleveland and East Cleveland, Ohio, birth cohorts (N = 31,415). Taking into account differences in risk factors, Black MIC infants experienced lower neonatal and endogenous mortality, but White MIC infants had higher postneonatal and exogenous mortality than their same race, non-MIC counterparts. Birthweight distributions were also more favorable for Black than White clients. We discuss the policy implications of our findings.