The heavier the better? Birthweight and perinatal mortality in different ethnic groups

BACKGROUND: Mother's ethnicity is associated with her baby's birthweight and risk of perinatal mortality. Given the close relation between birthweight and perinatal mortality, we explored whether ethnic differences in birthweight explain ethnic differences in perinatal mortality. METHODS: Data on all births to mothers born in Norway (808 658), Pakistan (6854), Vietnam (3283) and North Africa (1461) from 1980 to 1995 were obtained from the Medical Birth Registry of Norway. The associations between birthweight and perinatal mortality among ethnic groups were analysed using univariate and multivariate methods. RESULTS: Mean birthweights were low for Vietnamese and Pakistani mothers (3202 g, 3244 g) and high for Norwegian and North African mothers (3530 g, 3559 g). Mean birthweights were largely unrelated to perinatal mortality, which was lowest for Vietnamese (8.2/1000, 95% CI: 5.1-11.3) and highest for Pakistanis (14.9/1000, 95% CI: 12.0-17.7). Intermediate perinatal mortality rates were found among Norwegians (9.5/1000, 95% CI: 9.3-9.7) and North Africans (9.6/1000, 95% CI: 4.6-14.6). Further comparison of weight-specific mortality rates between the two largest ethnic groups showed the low birthweight paradox, where among low-weight births, perinatal mortality was lower among Pakistani than among Norwegian babies. However, adjustment to a relative birthweight scale (units of standard deviations from population-specific mean value) revealed higher rates of weight-specific mortality among Pakistanis across the entire range of birthweights. Multivariate adjustment for relative birthweight and other factors did not change these results. CONCLUSIONS: Differences in perinatal mortality between the ethnic groups were not explained by differences in mean birthweight. Paradoxical differences in birthweight-specific mortality rates could be resolved by adjustment to a relative scale.     

Association of head circumference at birth among sibling pairs

The objective of the study was to estimate and compare the correlation coefficients of head circumference and weight at birth among sibling pairs. Pairs of singleton siblings were ascertained among children born in Norway to the same mother between 1978 and 1997. Head circumference, birthweight and other perinatal factors were registered in the Medical Birth Registry of Norway. Head circumference measurements were obtained for first- and second-born in 287 448 sibling pairs. The correlation coefficient of head circumference among first- and second-born siblings was 0.343 (standard error 0.002) compared with 0.477 (standard error 0.002) for birthweight. These results were similar for later-born sibling pairs and only slightly influenced by other factors such as sex, fatherhood and time between pregnancies. Sensitivity analyses showed that substantial measurement error is required to explain the lower correlation for head circumference. In conclusion, the sibling correlation of head circumference was consistently weaker than that of birthweight.     

High-risk young mothers: infant mortality and morbidity in four areas in the United States, 1973-1978

An examination of the changes in infant mortality and morbidity in four regions in the United States has revealed high levels of health problems among the infants of two groups of mothers: those less than or equal to 17 years and 18-19 year-old multiparas, many of whom began their childbearing under age 18. Despite decreases over the period of observation, neonatal mortality rates remain over one and a half times as high for infants of these mothers as for other mothers, largely due to the relatively high proportion of low birthweight (LBW) infants born to these mothers. Post-neonatal mortality rates also remain high, and may be increasing; this change cannot be explained solely by differences in proportion of LBW infants between these and older mothers. Both the high post-neonatal mortality rates and the type of morbidity experienced by surviving infants is consistent with the socioeconomic disadvantage of young mothers. The data further indicate the limited resources available to these mothers to cope with their children's health needs, and their potential vulnerability to decreases in public programs supporting child health care.     

Impact of the Higgins Nutrition Intervention Program on birth weight: a within-mother analysis

A study was conducted to evaluate the impact of the Higgins Nutrition Intervention Program of individual nutritional assessment and rehabilitation on pregnancy outcome in a group of urban low-income women. Developed as an adjunct to routine prenatal care, the Higgins program utilizes an individualized approach to dietary treatment that combines an assessment of the risk profile for the presenting pregnancy with the application of specific nutritional rehabilitation allowances to compensate for the negative impact of diagnosed risks. This report presents results of analyses evaluating differences in birth outcomes between 552 sibling pairs; each mother had participated in the Higgins program during the pregnancy of the second-born, but not of the first-born, member of her pair. After adjustment for parity and sex, the intervention infants weighed an average of 107 gm more than their matched siblings at birth (p less than .01). The rate of low birth weight was 50% lower among the intervention infants than among their siblings (p less than .01); rates of intra-uterine growth retardation and perinatal mortality were also lower in the intervention group. The high risk of poor pregnancy outcome in this group of urban low-income women was reduced by the Higgins program.     

Reinterpreting the effects of maternal smoking on infant birthweight and perinatal mortality: a multivariate approach to birthweight standardization.

Infants of women who smoke during pregnancy have lower birthweights and have been observed to have higher rates of perinatal mortality than infants of non-smokers. It is not clear whether this increased risk of mortality is due to an excess of small births among smokers or to an independent effect of smoking. Although infants of smokers have overall higher mortality rates than non-smokers, low birthweight (< 2500 g) infants of smokers have lower mortality rates than low birthweight infants of non-smokers. However, comparison of birthweight-specific mortality between two groups is problematic when there are differences in the birthweight distributions. Methods that have been developed to standardize for these differences by comparing mortality rates relative to their own mean do not allow for simultaneous control of confounding variables. Using data from over 13,000 births of women who participated in a prepaid health care plan we present a method to standardize for birthweight while adjusting for variables that may confound the relationship between maternal smoking and perinatal mortality. After controlling for race, maternal age, education, parity, and number of cigarettes smoked, we found that 85% of the increased mortality due to smoking was attributable to an excess of small births in the birthweight distribution of offspring of smoking mothers, while 15% was due to higher birthweight-specific mortality at almost all standardized birthweights. Contrary to previous reports, we found that low birthweight infants of smoking mothers are at higher risk of perinatal mortality if a population-specific standard for birthweight is used.     

The health consequences of teenage fertility

A review of the literature on the health consequences of teenage pregnancy and childbirth shows remarkable similarity in findings from studies conducted in the United States, Canada, Britain, France and Sweden. In particular, results of studies conducted since 1970 have tended to indicate that the increased risk of maternal complications from pregnancy and delivery among teenagers--especially those older than 15--is associated more with socioeconomic factors than with the biological effects of age. Smaller differences in maternal mortality between teenagers and older women exist in England and Wales than in the United States and France; this finding suggests that England and Wales may have minimized the age or socioeconomic factors contributing to a difference in rates. Inadequate prenatal care may be a major cause of pregnancy-related complications for mothers, since teenagers in all countries are more likely than older mothers to seek care late in the pregnancy or not all. There is a very marked association between young age of mother and low birth weight in all countries. Sweden has the lowest rate of low birth weight at all maternal ages, and the United States generally has the highest. Some of the apparent effect of young maternal age on birth weight may be because the birth is likely to be the mother's first, and first births have a higher incidence of prematurity. As in the case of maternal health, inadequate prenatal care has been singled out as an important determinant of both prematurity and low birth weight. Late fetal death rates in the United States, England and Wales, and France are slightly higher among teenagers than among women in their 20s. In Canada and Sweden, however, no substantially increased risk for young women is found. Perinatal death rates, which one might expect to be influenced more by environmental factors than are late fetal deaths, show a more marked increase among infants of teenagers than do rates of late fetal deaths. Again, Sweden does not fit the pattern. Studies that separate data for young teens and older teenage mothers also indicate that increased perinatal and late fetal mortality rates may occur only among very young teenage mothers. There is no evidence of an overall increase in congenital malformations among babies born to teenagers. When individual birth defects are examined, some studies have shown increased rates of cardiovascular and central nervous system malformations among the children of teenage mothers.(ABSTRACT TRUNCATED AT 400 WORDS)     

Birthweight and perinatal mortality: III. Towards a new method of analysis

Perinatal mortality is closely related to birthweight. We propose a model that summarizes this relationship and provides a basis for the analysis of perinatal mortality. The components of this model are the frequency distribution of birthweight and the curve of weight-specific mortality. Taken together, these two curves completely describe perinatal mortality for a given population. The perinatal mortality of two populations can be meaningfully compared by plotting each weight-specific mortality curve relative to its own birthweight distribution. By this means, the excess mortality in one population can usually be expressed as the sum of two excess mortalities--one that occurs uniformly over the whole birthweight distribution, the other due to an increased number of small births. To illustrate this method, we analyse differences between white and black infants. We find that the excess mortality of black infants is chiefly due to an excess of small black births, but also to higher mortality over all (adjusted) birthweights. In contrast to other methods of analysis, the proposed method does not assume a priori that a difference in the mean birthweight of two populations is the cause of any difference in perinatal mortality. Furthermore, the proposed method is unbiased; in particular, it is preferable to direct or indirect standardization for birthweight, previously shown to be biased.     

Maternal smoking, birthweight and gestational age in sudden infant death syndrome (SIDS) babies and their surviving siblings

To evaluate the effect of maternal smoking on intrauterine growth of babies who died of sudden infant death syndrome (SIDS), birthweights of SIDS infants and their surviving siblings were compared with birthweights of infants in sibships were all infants survived the first year of life. We studied 184 349 mothers with at least two births registered in the population-based Swedish Medical Birth Registry during 1983–91. The mother being the unit of analysis, birthweight and gestational age of her infants were the repeated measures used in a repeated measures analysis of variance. Mothers whose first two infants survived at least 1 year, smoked less than mothers of SIDS infants, 25 and 41% ( P < 5 0.01). Overall, SIDS mothers did not smoke more while pregnant with the SIDS infant than while pregnant with the surviving sibling. SIDS siblings weighted, on average, 90 g less than infants in non-affected sibships. SIDS babies were even lighter, 193 g, and had 3.8 days shorter mean gestational age, compared with same birth-order babies in non-affected sibships. After adjustment for gestational age, the birthweight difference changed only slightly for SIDS siblings, while the difference for SIDS infants was reduced from 193 to 110 g. Further adjustment for smoking reduced the birthweight difference for SIDS siblings, from 74 to 50 g, and SIDS infants, from 110 to 82 g. Intrauterine growth retardation of sibships with a SIDS baby is explained only partly by maternal smoking. The even lower birthweight of the SIDS baby, resulting from shorter gestational age, cannot be explained by smoking, suggesting pregnancy factors specific to the SIDS baby and not to its siblings.     

Another look at the black-white gap in gestation-specific perinatal mortality.

In the US, black infants born near or at term experience higher mortality than white infants. To extend our understanding of black-white differences in the relative advantages of growth (measured by birthweight) for gestational age, we compared race-specific rates of perinatal mortality by deviation in grams from the median birthweight for four categories of gestation (35-36, 37-38, 39-41, and 42-43 weeks). We also used race-specific standards to examine the difference between the median birthweight and the optimum birthweight (i.e. birthweight with the lowest mortality). The data, which were derived from vital records for singletons delivered in the US from 1983-1984, comprised 24,626 fetal and neonatal deaths among 5,157,197 white infants and 5973 fetal and neonatal deaths among 926,678 black infants. At all deviations from the median birthweight, black infants had relatively better survival at 35-36 weeks of gestation. This advantage was reversed among infants with gestations of 39-41 and 42-43 weeks. The optimum birthweight for black infants with gestations greater than or equal to 37 weeks was closer to their median birthweight than was that for white infants. For black infants with gestations of 39-41 weeks, the optimum birthweight was 187g (95% confidence interval (CI): 150-234) greater than the median birthweight (3289g); for comparable white infants the optimum birthweight was 397g (95% CI: 366-431) greater than the median birthweight (3487g). To reduce the black-white gap in perinatal mortality, we need a better understanding of aetiological relations between gestation, growth, and mortality.     

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.     

US Black vs White disparities in foetal growth: physiological or pathological?

BACKGROUND: Birthweight for gestational age is lower in US Black infants than in US White infants. It is unknown, however, whether this difference is 'normal' (i.e. physiological) or reflects pathological foetal growth restriction. METHODS: We applied an analytic approach based on foetuses at risk to compare gestational age-specific rates of live birth, 'revealed' small-for-gestational-age (SGA), and neonatal mortality among singleton infants >or=22 weeks of gestation and >or=500 g born in 1998-2000 to US White (n = 9 012 194), US-born Black (n = 1 554 382), and foreign-born Black (n = 200 395) mothers. Graphical methods and Cox proportional hazards regression analyses were used to compare outcomes in the three ethnic groups. RESULTS: Rates of live birth and neonatal mortality were highest at all gestational ages in US-born Blacks, lowest in Whites, and intermediate in foreign-born Blacks. The revealed SGA pattern cohered much more closely with the observed pattern for neonatal mortality when SGA was defined based on a single, overall standard of birthweight for gestational age than when based on ethnic group-specific standards. CONCLUSION: The closer coherence of revealed SGA and neonatal mortality rates based on a single standard and the intermediate pattern among foreign-born Blacks strongly suggest that Black-White differences in birthweight for gestational age are pathological, rather than physiological.     

Racial and ethnic differences in perinatal mortality: the role of fetal death

PURPOSE: We investigate whether variations in infant mortality rates among racial/ethnic groups could be explained by variations in fetal mortality rates where relatively higher infant mortality rates may correspond to lower fetal mortality rates due to possible systematic differences in reporting of fetal death compared to live births. METHODS: Using US perinatal data from 1995 to 1999, we calculated crude mortality rates, birth weight-specific fetal and hebdomadal mortality rates, risks of perinatal death, and the risk of being classified as a fetal death versus other period death among infants born to Non-Hispanic White, Non-Hispanic Black, and Hispanic mothers. RESULTS: Two-fold disparities between Whites and Blacks persist for all mortality categories. Black low birth-weight deliveries, compared to Whites, have perinatal advantages in both fetal and hebdomadal periods. Hispanics were less likely than Whites to be reported as a fetal versus a hebdomadal death. CONCLUSIONS: While these data suggest some underreporting of Black fetal deaths, they provide little evidence that Black-White disparities in infant mortality are a function of variations in classifying a death occurring at delivery as either a fetal death or as a live birth-infant death. These data suggest that the lack of a White-Hispanic disparity in fetal mortality rates may be influenced by underreporting.     

Trends in reporting of maternal drug abuse and infant mortality among drug-exposed infants in New York City

New York City trends in maternal drug abuse during pregnancy and in mortality rates for infants with in utero drug exposure are reported; causes of death among drug-exposed infants are studied, as is the association between maternal drug abuse and other factors that contribute to infant mortality (e.g., low birthweight, lack of prenatal care). Data for this study are derived from the linked files of New York City birth and infant death certificates. Reports of infants born to drug abusing mothers increased from 6.7 per 1000 live births in 1981 to 20.3 per 1000 live births in 1987, with abuse of cocaine accounting for most of the rise. When standardized for race and ethnicity, the mortality rate for drug-exposed infants born from 1978 through 1986 was 35.9, or 2.4 times that for infants in New York City in general. Drug-exposed infants were over three times as likely as infants in the general population to be of low birthweight. The association of both opiates and cocaine with increased mortality and low birthweight was similar. Death rates from SIDS and AIDS were especially higher for drug-exposed infants than for those in the general population, and were similar for opiate- and cocaine-exposed infants. The impact of drug abuse on infant mortality rates in selected low socioeconomic health districts is discussed.     

The intergenerational relationship between mother's birthweight, infant birthweight and infant mortality in black and white mothers

Summary. The relationship between the birthweight of white and black mothers and the outcomes of their infants were examined using the 1988 National Maternal and Infant Health Survey. White and black women who were low birthweight themselves were at increased risk of delivering very low birthweight (VLBW), moderately low birthweight (MLBW), extremely preterm and small size for gestational age (SGA) infants. Adjustment for the confounding effects of prepregnant weight and height reduced the risks of all these outcomes slightly, and more substantially reduced the maternal birthweight associated risk of moderately low birthweight among white mothers. There was little effect of maternal birthweight on infant birthweight-specific infant mortality in white mothers; however, black mothers who weighed less than 4 lbs at birth were at significantly increased risk of delivering a normal birthweight infant who subsequently died. Although the risks for the various outcomes associated with low maternal birthweight were not consistently higher in black mothers compared with white mothers, adjustment for prepregnant weight and height had a greater effect in white mothers than in black mothers. We suggest that interventions to reduce the risks for adverse pregnancy outcomes associated with low maternal birthweight should attempt to optimise prepregnant weight and foster child health and growth.     

Maternal education as a modifier of the association between low birthweight and infant mortality

Both low birthweight (LBW) and infant mortality rate (IMR) have been consistently shown to be associated with maternal level of educational attainment. This paper examines the mortality risk attributable to LBW in different levels of maternal education. Comprising the study population were 18,715 singleton live births to Jewish mothers ages 20-39, during the years 1977-1980 in the Negev (the southern part of Israel). Data were obtained from a linked record of birth and death certificates. As expected, proportions of LBW (less than 2500 grams) were inversely related to level of maternal education (12.2% in the lowest educational level, 7.9% and 8.0% in the two intermediate levels, and 7.2% in the highest educational level). The mortality risk attributed to LBW was found to be modified by maternal level of education. Mortality ratios standardized for maternal age and parity were computed, using educational level 3, where the lowest mortality rates were observed, as the standard population. Among LBW infants no significant differences were found across educational levels, except for the lowest educational level where only 69% of the expected number of deaths were observed. The survival advantage of LBW infants in the lowest educational level was observed both in the neonatal and the postneonatal periods. Among normal birthweight (NBW) infants, a statistically significant excess mortality was detected both in the highest and the lowest educational levels. The excess mortality of NBW infants in the highest level of maternal education was due to neonatal mortality (SMR = 2.2), while the excess mortality in this birthweight category in the lowest educational level occur mainly in the postneonatal period (SMR = 2.4).(ABSTRACT TRUNCATED AT 250 WORDS)     

Rising Infant Mortality in Delaware: An Examination of Racial Differences in Secular Trends

Objectives: Recent increases in the Delaware Infant Mortality Rate (IMR) have been attributed to a rise in the mortality of very low birth weight (VLBW, <1500 g) infants born to mothers of higher socioeconomic status. This study examines whether the determinants of infant mortality trends in Delaware vary by race. Methods: Linked birth/infant death cohort files for the two periods 1993–1997 and 1998–2002 were used to evaluate the determinants of infant mortality trends separately for White and Black racial groups. Kitagawa analyses determined the components of race-specific infant mortality trends attributable to changes in both the birthweight distribution and birthweight-specific mortality rates. Maternal characteristics were examined to identify factors associated with IMR changes. Results: Between the two time periods, infant mortality increased 23% among White infants and 17% among Black infants. For both races, the infant mortality increase was explained by increases in the incidence and mortality of VLBW infants, specifically below <500 grams for Blacks and <1,000 grams for Whites. The increased incidence of VLBW deliveries was statistically significant only among Whites, almost 40% of which was explained by an increase in multiple births. For both Whites and Blacks, the increase in VLBW mortality occurred mainly among births to more traditionally advantaged women who were twenty or older, at least high school educated, married, privately insured, had received first trimester prenatal care, and those who delivered multiple births. Conclusions: These findings suggest that conventional strategies of increasing access to prenatal care among disadvantaged women may be insufficient to reverse recent IMR increases in Delaware, irrespective of race. Future efforts should focus on understanding the causes of the increased infant mortality associated with higher socioeconomic status, including changes in assisted reproductive technology utilization, maternal health status, and obstetric practice.     

Trends in perinatal characteristics in South Australia, 1981 to 1994, by place of residence of mother

Abstract: We investigated differentials and time trends in perinatal mortality and perinatal risk factors by geographic area of residence in South Australia during 1981–1994, to assess whether sociodemographic inequalities had lessened. The areas analysed were Adelaide and the country region of South Australia, with Adelaide being divided by socioeconomic status into two areas. Subjects were 267 116 singleton births of at least 400 g birthweight (or at least 20 weeks' gestation) notified to the state's perinatal data collection. Year of birth, residential area, and interactions between year of birth and residential area were analysed as predictors of perinatal risk factors and deaths. There was a statistically significant decline in the perinatal death rate in all residential areas (mainly because of a decrease in neonatal deaths), which did not vary significantly by area. The frequency of low birthweight (< 2500 g) increased in the country areas and in the lower socioeconomic areas of Adelaide, but not in the higher socioeconomic areas. Although premature births increased in all areas, the increase was less pronounced for the higher socioeconomic areas of Adelaide. By comparison, although all areas showed an increase in the proportions of mothers aged 35 years or over, the increase was larger for the higher socioeconomic areas. Australia has a national policy of reducing social inequalities in health status. Perinatal mortality rates declined in Adelaide and country residential areas from 1981 to 1994. This trend is favourable, but from the relativities of these rates by residential area, there is not compelling evidence of a reduction in inequalities.     

Perinatal Care in Canada

HEALTH ISSUE: Canada's standard of perinatal care ranks among the highest in the world, but there is still room for improvement, both in terms of regional differences in care and global comparisons of approaches to care in Canada and elsewhere. Data from the Canadian Perinatal Surveillance System (CPSS) was used to evaluate morbidity and mortality among mothers and infants. KEY FINDINGS: Maternal mortality rates in Canada dropped to 4.4 per 100,000 live births in 1993-1997 and are among the lowest in the world. Rates of Caesarean section increased from 15.3 per 100 deliveries in 1994 to 19.1 in 1997. Although the infant mortality rate in Canada is among the lowest in the world (5.3-8.8 per 1,000 live births 1990-2000), there are unacceptable disparities between subpopulations. In Aboriginal populations, rates of stillbirth and perinatal mortality are 2-2.5 times the Canadian average. There has been a steady increase in the proportion of births among older women who have the highest risk of preterm births and pregnancy complications.The increasing rate of multiple births has accelerated recently and is of concern as these carry a higher risk of complications and are associated with an increased risk of preterm birth. The costs to the health care system are likely to be high. DATA GAPS AND RECOMMENDATIONS: CPSS data, including economic indicators, needs to be collected in a more timely and uniform manner across Canada. The CPSS should provide an evaluation of how well Canada fares in relation to international standards of perinatal care.