Relationship of ergonomic stressors to birthweight and gestational age.

Women in many occupations are exposed to ergonomic stressors (eg, prolonged standing, physical exertion, and long work weeks). After a consideration of the major methodological problems encountered in studying effects of ergonomic stressors on birthweight and gestational age, epidemiologic studies that have addressed this issue are reviewed. No individual ergonomic stressor has been consistently associated with effects on gestational age. However, most studies which have attempted to look at the cumulative effect of several stressors report that women in the highest exposure category are at higher risk of giving birth prematurely. In contrast, data regarding an association with birthweight are more variable, and firm conclusions cannot be drawn. While future studies that assess exposure to ergonomic stressors with a more comprehensive and quantitative approach are needed, current evidence is sufficient to suggest that clinicians should take ergonomic stressors into account in the assessment of their patients' risk for preterm delivery.     

Estimation of individual neonatal survival using birthweight and gestational age: a way to improve neonatal care

The study was conducted to determine the combined effect of birthweight and gestational age at birth on neonatal mortality using individually-identified livebirths. Logistic regression was used for studying the interactive effect of birthweight and gestational age on the individual probability of neonatal death. All livebirths from Chile in 2000 were included in a linked file. Odds ratio models for birthweight and gestational age were developed for each sex. The probability of neonatal death by sex was presented using contour plots. The models were statistically significant, and odds ratios were different and non-linear for the effects of birthweight and gestational age. Contour plots of constant neonatal mortality according to birthweight and gestational age were presented; they were similar for each sex. A single graph for both sexes that estimates the survival potential of infants born too early or too small would improve neonatal care in developing countries.     

Racial differences in birthweight for gestational age and infant mortality in extremely-low-risk US populations

Using national data, we develop and contrast the birth-weight percentiles for gestational age by infants of extremely-low-risk (ELR) White and African-American women and examine racial differences in the proportion of small-for-gestational-age (SGA) births. We then scrutinise racial variations in infant mortality rates of the infants of ELR women. We further compare the infant mortality rates of infants at or below the 10th percentile of birthweight for gestational age of each race group to determine whether infants with similar restricted fetal growth have comparable risks of subsequent mortality. Single live births, 34-42 weeks' gestation, to White and African-American US-resident mothers were selected from the 1990-91 US Linked Live Birth--Infant Death File (n = 4,360,829). Extremely-low-risk mothers were defined as: married, aged 20-34 years, 13+ years of education, multiparae, with average parity for age, adequate prenatal care, vaginal delivery, and no reports of medical risk factors, tobacco use or alcohol use during pregnancy. Marked racial variation in birthweight percentiles by gestational age was evident. Compared with ELR White mothers, the risk of an SGA infant was 2.64 times greater for ELR African-American mothers and the risk of infant mortality was 1.61 times greater. For the ELR group, the infant mortality rates of African-American and White infants at or below the 10th percentile of birthweight for gestational age of their respective maternal race group were essentially identical after controlling for gestational age. In conclusion, race differences in fetal growth patterns remained after controlling for risk status. Efforts to remove racial disparities in infant mortality will need to develop aetiological pathways that can explain why African-Americans have relatively higher rates of preterm birth and higher infant mortality rates among term and non-SGA infants.     

Racial differences in the relation of birth weight and gestational age to neonatal mortality

Utilizing South Carolina live birth-infant death cohort files for the period 1975-80, this study examines the bivariate distribution of birth weight-gestational age (BW-GA), intrauterine growth curves, and BW-GA specific neonatal mortality rates (NMRs) by race. Comparison of BW-GA distributions revealed an appreciable shift between racial subgroups. Nonwhites, on the average, were born 1 week earlier and 270 grams lighter in weight than whites. In addition to racial differences in rates of intrauterine growth, nonwhites experienced lower BW-GA NMRs than whites in BW-GA categories less than 3,000 grams and less than 38 weeks. However, the improved mortality experience of nonwhites at more immature BW-GA categories was not consistently present when different cause-specific NMRs were considered. These persistent racial variations highlight continuing issues regarding both the use of a single norm for defining low birth weight or prematurity and the role of nonsocioeconomic factors related to racial BW-GA distribution and mortality disparities. As birth weight and gestational age represent empirical indicators of the maturity and survivability of an infant at birth, these data and previous supporting research raise further concerns regarding the ability of these indicators to accurately reflect equivalent fetal development and subsequent risk of mortality among racial groups.     

Decreasing gestational age and birthweight in spastic diplegia

Over a 4-year period a significant fall occurred in the mean birthweight and mean gestational age of prematurely born children who subsequently developed spastic diplegia. This coincided with a considerable improvement in perinatal mortality in the unit in which they were delivered. However, although the number of premature deliveries remained stable, the disorder did not become less common. No specific aetiological factors were identified, but the 24 affected children frequently had a history of adverse prenatal or perinatal factors. We conclude that high standards of obstetric and neonatal care prevent the subsequent development of spastic diplegia in low birthweight infants. However, these factors have also improved the survival of very low birthweight infants who have a much higher risk for the disorder and this has prevented a significant reduction in its frequency.     

Does gestational age in combination with birthweight provide better statistical adjustment of neonatal mortality rates than birthweight alone?

Between-area comparisons of neonatal mortality rates should be adjusted for differences in the underlying mortality risk. The traditional approach to this problem is to adjust neonatal mortality rates statistically for between-area differences in the birthweight distributions. However, in other types of perinatal research, birthweight is usually considered in combination with gestational age. For between-area comparisons of neonatal mortality rates, some researchers have argued that adjustment by gestational age in addition to birthweight might not be necessary. This present study used graphical methods based on a non-parametric version of Poisson regression to underline the importance of examining neonatal mortality rates by both gestational age and birthweight. Six years of data from a whole-population database (Queensland Perinatal Data Collection) were used. The analysis also illustrates the value of non-parametric modelling in perinatal epidemiology.     

Racial differences in temporal changes in newborn viability and survival by gestational age

This study examines trends in the rates of very preterm, moderately preterm and gestational age-specific neonatal mortality, and in the gestational age limit of viability in South Carolina (SC) from 1975 to 1994. We also investigate whether trends were similar between African-Americans and Whites. We hypothesised that disproportionate reductions in gestational age-specific mortality, rather than any major changes in the gestational age distributions of either race group, underlie any increasing racial disparity in overall mortality rates. During 1975-94, single livebirths, who were born to mothers resident in SC and were either White or African-American based on recorded maternal race, were selected for the investigation. We define the gestational age limit of viability as the gestational age at which > or = 50% of infants in the population died within 28 days of life. Although preterm percentages have not improved, there was a marked decline in neonatal mortality. Gestational age-specific neonatal mortality decreased for both race groups, although there were greater reductions for White preterm infants. By the end of the study period, the African-American neonatal mortality rate was 2.3 times that of Whites and the gestational age at which 50% of newborns died within 28 days of life was 24.5 weeks for Whites and 23.9 weeks for African-Americans. The ongoing decline in neonatal mortality continues to be mainly due to reductions in gestational age-specific neonatal mortality, probably related to high-risk obstetric and neonatal care. Technological developments in these areas may have differentially benefited Whites, resulting in an increasing racial disparity in neonatal mortality rates. Preterm African-American infants no longer have a marked survival advantage over White infants, even at the gestational age limit of viability.     

Optimal gestational age and birth-weight cutoffs to predict neonatal morbidity.

BACKGROUND: Gestational age (GA) and birth weight (BW) criteria are used to identify newborns at risk for neonatal morbidity. Currently, preterm is GA less than 37 weeks; low birth weight is BW less than 2,500 grams; and small for gestational age (SGA) is BW less than the tenth percentile weight for the infant's GA. The optimal classification system balances the misclassification cost of false negatives against the cost of false positives. OBJECTIVE: To calculate the relative misclassification costs implied by the current 37-week and 2,500-gram cutoffs, and to test the validity of the current definition of SGA as a predictor of term morbidities. METHODS: GA, BW, and morbidity information were collected for 22,606 infants born between July 1981 and December 1992. Using this dataset, logistic regression coefficients were obtained modeling GA or BW as predictors of morbidities associated with prematurity. For a subset of 18,813 infants with GAs between 37 and 41 weeks, coefficients were obtained modeling both GA and BW as independent predictors of term morbidities. The logistic regression coefficients were used to calculate optimal birth weight, gestational age, and birth-weight-for-gestational-age cutoffs. RESULTS: The current definitions of low birth weight and preterm imply that it is 18 to 28 times more costly to misclassify a sick infant as low-risk than to misclassify a well infant as high-risk. CONCLUSIONS: Gestational age alone is better than birth weight alone at predicting preterm morbidities. No birth-weight cutoff can adequately predict term morbidities. A single weight-percentile cutoff for all gestational ages should not be used to identify newborns at high risk for neonatal morbidity.     

Modulation off birthweight through gestational age and fetal growth

Summary Several factors are known to affect birthweight and their effects are variously mediated through gestational duration or through fetal growth conditional on this gestation, in order to quantify independent associations of birthweight conditional and unconditional on gestational age, all 2538 mothers of singleton babies delivered during 1993 in two Maternity Hospitals in Athens were interviewed and their obstetric records abstracted. Birthweight was modelled as outcome variable through multiple regression including 32 potentially predictive factors. The regression model was fitted with and without gestational age as an additional independent variable in order to apportion birthweight associations into those independent of, or mediated through, gestational length. The factors studied were found to be classifiable into the following categories: factors associated with birthweight mostly through increases in gestational duration, either positively (age at menarche, long menstrual cycles, parity 4 or higher), or negatively (single motherhood, maternal age, tobacco smoking); those associated with birthweight mostly through increase of birthweight conditional on gestational duration, either positively (male gender, short menstrual cycles, maternal pre-pregnancy weight, anaemia, oedema) or inversely (employment during pregnancy, stillbirth, primiparity, pregnancy induced hypertension, coffee drinking); and those associated with birthweight through apparently dual effects, either positively (maternal education) or inversely (perceived stress, bleeding during pregnancy). The other studied factors were not demonstrably related to birthweight in this data set. Identification and quantification of these relations is useful for understanding underlying physiological and pathophysiological processes and for increasing specificity in exploring the association of birthweight with adult onset diseases, like coronary heart disease or cancer.     

The contrasting effects of parental birthweight and gestational age on the birthweight of offspring

Investigations on intergenerational effects on birthweight have been carried out using the data of the 1958 British National Birthday Trust Fund cohort and its follow-up to 23 years, the National Child Development Study (NCDS-4), which included information on all births to cohort members by that age. This report is directed particularly at ascertaining the independent effect of parental gestational age on babies' birthweight. The two main findings are a direct association between parental and offspring birthweight (significant for both mothers and fathers after allowing for confounding factors), but an inverse association with parental gestational age (significant only for the mothers). It is postulated that at least part of this effect is mediated through the association between maternal fetal growth rate and their babies' birthweight; the faster the rate the shorter the gestational age for a given birthweight. It was not possible to ascertain what part genetic factors played in this relationship. Larger and more informative intergenerational studies are needed to further knowledge on this question.     

胎龄别新生儿出生体重分析

【目的】 建立以人群为基础的胎龄别新生儿出生体重百分位数修匀曲线。 【方法】 对北京市顺义区医院及顺义区妇幼保健院2009年11月1日-2011年1月21日出生的新生儿进行出生体重的标准化测量,选择符合正常母亲标准的单胎活产新生儿出生体重建立数据库。采用偏度-中位数-变异系数法修匀百分位数。将结果与1986-1987年中国15市新生儿体格发育调查进行比较。 【结果】 共5 068例新生儿纳入到研究中,获得了顺义区正常单胎活产新生儿胎龄别出生体重P3,P10,P25,P50,P75,P90,P97修匀曲线。性别差异具统计学意义(P<0.05)。其中小于胎龄儿发生率为9.39%,大于胎龄儿发生率为9.21%。与15市调查比较,在35~43周的胎龄别出生体重均数差异具统计学意义(P<0.05)。 【结论】 本研究建立了北京市顺义区胎龄别新生儿出生体重百分位数修匀曲线,为该地区及其它类似地区评估胎儿生长发育提供了较新的参考依据。     

Impact of pregnancy-induced hypertension on birthweight by gestational age

Few studies to date have examined the effect of severe pre-eclampsia, pre-eclampsia, and gestational hypertension on birthweight according to gestational age. We conducted a population-based retrospective cohort study of 16,936 pregnant women in Suzhou, China. Analysis of variance and multivariable linear regression were performed to compare the mean birthweights of babies born to mothers with gestational hypertension, pre-eclampsia, and severe pre-eclampsia with birthweights of infants born to mothers with normal blood pressure at each week of gestation. The differences in mean birthweight between women with severe pre-eclampsia and women with normal blood pressure ranged between -467.7 g and 189.1 g. The birthweights were statistically significantly lower in women with severe pre-eclampsia than in women with normal blood pressure for gestational age categories < or = 35 and 36 weeks. However, after adjustment for confounding variables, the birthweights were not statistically significantly different in women with severe pre-eclampsia when compared with women with normal blood pressure even at < or = 35 and 36 weeks. The differences in mean birthweight between women with pre-eclampsia and women with normal blood pressure ranged between -132.2 g and 174.6 g. These differences were not statistically significant, before or after adjusting for confounding variables. There were no differences in mean birthweight between women with gestational hypertension and women with normal blood pressure. Further analysis suggested that pre-eclampsia and gestational hypertension were associated with increased rates of both small-for-gestational-age and large-for-gestational-age infants. The majority of the babies born to mothers with different types of pregnancy-induced hypertension were appropriate-for-gestational-age or even large-for-gestational-age. In this Chinese population, most babies born to mothers with severe pre-eclampsia or pre-eclampsia and gestational hypertension had similar fetal growth to those born to normotensive mothers.     

Sex and age differences in luteoskyrin hepatotoxicity

1. Luteoskyrin, a hepatotoxic and hepatocarcinogenic mycotoxin from the fungus of "yellowed rice" Penicillium islandicum Sopp, shows different toxicities depending on the age and sex in mice. The lethal toxicity was higher in young or male mice than in adult or female mice. 2. 3H-luteoskyrin was accumulated in the livers, especially in their mitochondria, of suckling or male mice in larger amounts than in those of adult and female mice. 3. Intravenously injected 3H-luteoskyrin was excreted into the feces more rapidly in female than in male mice. 4. Luteoskyrin added to a diet was accumulated in the liver at a much higher rate in male than in female mice. 5. The susceptibility of mice to luteoskyrin hepatotoxicity slowly correlates to the rate of its accumulation in their livers, which in turn reflects the rate of its biliary excretion.     

The quality and completeness of birthweight and gestational age data in computerized birth files.

Computerized birth files compiled by the State of North Carolina for the years 1975-1977 were analyzed for omissions and inaccuracies. A wide range in the per cent missing values was found for different data items, from essentially none missing (birthweight, sex, race) to about 20 per cent missing (gestational age, paternal social data). Recorded birthweight showed the expected skewing from a normal distribution. The only demonstrable inaccuracy was in the form of digit preference, probably causing errors of +/- 1 oz (28.3 g). Reported gestational ages were more suspect, falling outside the range of biologically plausible gestation length in 2.8 per cent of cases. An additional 1.5 per cent of gestational ages were found to be misdated by four to 20 weeks based on the observed bimodal weight distributions among births of the same reported gestational age. Hospitals of various sizes and administrative affiliations submitted records with missing or inaccurate gestational age data with roughly equal frequency. These records were found to come from a socio-demographically high-risk subpopulation. The implications of elimination of incomplete or erroneous birth record data in perinatal epidemiologic research are discussed.     

Access to intensive neonatal care and neonatal survival in low birthweight infants: A population study in Norway

This study evaluates the impact of regional differences in access to intensive neonatal care on neonatal survival in geographically defined populations of 4,692 low birthweight births in Norway 1979-81. For infants weighting 1,250 to 2,499 g our results are consistent with the existence of a dose-response association between neonatal survival and the level of immediate access to intensive neonatal care. Although not statistically significant, there was a clear gradient in the risk of mortality within 24 hours. A similar pattern of survival could not be consistently demonstrated for infants weighing less than 1,250 g.     

Joint Bayesian analysis of birthweight and censored gestational age using finite mixture models

Birthweight and gestational age are closely related and represent important indicators of a healthy pregnancy. Customary modeling for birthweight is conditional on gestational age. However, joint modeling directly addresses the relationship between gestational age and birthweight, and provides increased flexibility and interpretation as well as a strategy to avoid using gestational age as an intermediate variable. Previous proposals have utilized finite mixtures of bivariate regression models to incorporate well‐established risk factors into analysis (e.g. sex and birth order of the baby, maternal age, race, and tobacco use) while examining the non‐Gaussian shape of the joint birthweight and gestational age distribution. We build on this approach by demonstrating the inferential (prognostic) benefits of joint modeling (e.g. investigation of ‘age inappropriate’ outcomes like small for gestational age) and hence re‐emphasize the importance of capturing the non‐Gaussian distributional shapes. We additionally extend current models through a latent specification which admits interval‐censored gestational age. We work within a Bayesian framework which enables inference beyond customary parameter estimation and prediction as well as exact uncertainty assessment. The model is applied to a portion of the 2003–2006 North Carolina Detailed Birth Record data (n=336129) available through the Children's Environmental Health Initiative and is fitted using the Bayesian methodology and Markov chain Monte Carlo approaches. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of gestational age misclassification on the pattern of low birthweight in Aborigines

Abstract: Are most births of Aboriginal babies with low birthweight preterm or full term? There is no consensus because of the difficulty in obtaining valid measurements of gestational age. In Queensland, between 1988 and 1992, there were 519 births of Aboriginal babies with low birthweight in excess of the number expected if Aborigines had the same risk of low birthweight as whites. Most of these were preterm (males 76 per cent, females 65 per cent). Sensitivity analyses were used to investigate whether this result was robust to gestational age misclassification. Implausibly large misclassification proportions were required to make preterm low birthweight an insignificant contributor to the low birthweight excess in Aborigines. Therefore, efforts to reduce the number of preterm births should be given high priority. Unfortunately, significant reductions in the number of preterm births will not be achieved by reducing the prevalence of traditional risk factors for full–term low birthweight (for example, maternal smoking, teenage pregnancy). More work is needed to identify potentially modifiable risk factors for preterm birth.     

A nationwide investigation on gestational age specific birthweight and mortality among Japanese twins

Gestational age specific birthweight has been used as an important indicator to identify the health status of neonates and to provide appropriate neonatal care services to those at high risk. To identify the gestational age specific birthweight of twins born in secondary and tertiary hospitals in Japan and to explore factors affecting mortality, we used a nationwide obstetric database in Japan. Liveborn twins from 2001 to 2005 in the database, which was established with the national Perinatal Health Care Project, were enrolled (n=22,240). Obstetric data from the medical records were collected and analysed. Approximately 60% of liveborn twins were delivered between weeks 33 and 38, most frequently at 36 and 37 weeks. The mean birthweight of liveborn twins was 2084 g and the mean gestational age was 34.9 weeks. Intrauterine growth differed by parity, mode of delivery, birth order, chorionicity and sex. Using logistic regression, lower gestational age, small for gestational age, monochorionic twins and vaginal delivery tended to have higher risks of mortality.     

Energy-nitrogen balances and protein turnover in small and appropriate for gestational age low birthweight infants

The aim of the present study was to compare, under the same nursing conditions, the energy-nitrogen balance and the protein turnover in small for gestational age (SGA) and appropriate for gestational age (AGA) low birthweight infants. We compared 8 SGA's (mean +/- s.d.: gestational age 35 +/- 2 weeks, birthweight 1520 +/- 330 g) to 11 AGA premature infants (32 +/- 2 weeks, birthweight 1560 +/- 240 g). When their rate of weight gain was above 15 g/kg/d (17.6 +/- 3.0 and 18.2 +/- 2.6 g/kg/d, mean postnatal age 18 +/- 10 and 20 +/- 9 d respectively) they were studied with respect to their metabolizable energy intake, their energy expenditure, their energy and protein gain and their protein turnover. Energy balance was assessed by the difference between metabolizable energy and energy expenditure as measured by indirect calorimetry. Protein gain was calculated from the amount of retained nitrogen. Protein turnover was estimated by a stable isotope enrichment technique using repeated nasogastric administration of 15N-glycine for 72 h. Although there was no difference in their metabolizable energy intakes (110 +/- 12 versus 108 +/- 11 kcal/kg/d), SGA's had a higher rate of resting energy expenditure (64 +/- 8 versus 57 +/- 8 kcal/kg/d, P less than 0.05). Protein gain and composition of weight gain was very similar in both groups (2.0 +/- 0.4 versus 2.1 +/- 0.4 g protein/kg/d; 3.5 +/- 1.1 versus 3.3 +/- 1.4 g fat/kg/d in SGA's and AGA's respectively). However, the rate of protein synthesis was significantly lower in SGA's (7.7 +/- 1.6 g/kg/d) as compared to AGA's (9.7 +/- 2.8 g/kg/d; P less than 0.05). It is concluded that SGA's have a more efficient protein gain/protein synthesis ratio since for the same weight and protein gains, SGA's show a 20 per cent slower protein turnover. They might therefore tolerate slightly higher protein intakes. Postconceptional age seems to be an important factor in the regulation of protein turnover.     

Low birthweight, preterm, and small for gestational age babies in Scotland, 1981-1984.

STUDY OBJECTIVE--The aim was to examine the effect of maternal age, gravidity, marital status, previous perinatal deaths, and parental social class on babies born low birthweight, preterm, and small for gestational age. DESIGN--The study used data on discharge summaries from all maternity hospitals in Scotland. SETTING--The study was based on all singleton deliveries in Scotland. PARTICIPANTS--The analysis involved information on 259,462 singleton babies born during the four years 1981-84 in Scotland. MEASUREMENTS AND MAIN RESULTS--Previous perinatal death was found to be the strongest predictor for both preterm and low birthweight. Single mothers were at particularly high risk of having a small for gestational age baby and those who were previously married of having a preterm baby. Women aged less than 20 years old, those over 34 years old, nulligravidae, and those of parity 3 or more were also at increased risk of adverse pregnancy outcome. Mothers and fathers in manual social classes and those who could not be assigned a social class on the basis of their occupation were at increased risk for all three adverse outcomes studied. The babies of parents who were in manual occupations were twice as likely as those of parents in non-manual occupations to be small for gestational age and almost twice as likely to be low birthweight. CONCLUSIONS--Mother's social class is a risk factor for adverse pregnancy outcome independent of maternal age, parity, and adverse reproductive history, and also independent of father's social class. Information on both parents' occupations should be collected in maternity discharge systems.