Birth Weight Distribution Research Articles

Influence of Parental Overweight on the Association of Birth Weight and Fat Distribution Later in Childhood

Objective: To examine whether the association between birth weight and fat distribution in childhood is modified by parental overweight. Methods: Cross-sectional study of 728 Danish children aged 8–10 and 14–16 years. The main outcomes were waist circumference, waist-to-height ratio, subscapular skinfold, and subscapular-to-triceps skinfold ratio. Analyses were stratified by parental overweight status (none vs. ≥1 overweight parent) for each dependent variable, expressed as z-scores. Results: Birth weight z-score was negatively associated with waist circumference (β –0.08 SD; 95% CI –0.15, –0.02), waist-to-height ratio (β –0.15 SD; 95% CI –0.22, –0.07), and subscapular-to-triceps ratio (β –0.28 SD; 95% CI –0.44, –0.12) after adjustment for sex, age, puberty, preterm birth, BMI, height, socio-economic status, mother’s age at delivery, parity, breastfeeding, energy intake, and aerobic fitness in the group with ≥1 overweight parent. Birth weight was negatively associated with subscapular skinfold in groups with (β –0.16 SD; 95% CI –0.24, –0.06) and without overweight parents (β –0.09 SD; 95% CI –0.16, –0.02), but the magnitude of the association was greater in the former group. Conclusion: The association between birth weight and fat distribution seems to be influenced by parental overweight. Lower birth weights are associated with central adiposity among offspring of overweight parents.

Birth statistics of high birth weight infants (macrosomia) in Korea

PurposeThe authors analyzed the trend from the birth-related statistics of high birth weight infants (HBWIs) over 50 years in Korea from 1960 to 2010.MethodsWe used 2 data sources, namely, the hospital units (1960's to 1990's) and Statistics Korea (1993 to 2010). The analyses include the incidence of HBWIs, birth weight distribution, sex ratio, and the relationship of HBWI to maternal age.ResultsThe hospital unit data indicated the incidence of HBWI as 3 to 7% in the 1960's and 1970's and 4 to 7% in the 1980's and 1990's. Data from Statistics Korea indicated the percentages of HBWIs among total live births decreased over the years: 6.7% (1993), 6.3% (1995), 5.1% (2000), 4.5% (2000), and 3.5% (2010). In HBWIs, the birth weight rages and percentage of incidence in infants' were 4.0 to 4.4 kg (90.3%), 4.5 to 4.9 kg (8.8%), 5.0 to 5.4 kg (0.8%), 5.5 to 5.9 kg (0.1%), and >6.0 kg (0.0%) in 2000 but were 92.2%, 7.2%, 0.6%, 0.0%, and 0.0% in 2009. The male to female ratio of HBWIs was 1.89 in 1993 and 1.84 in 2010. In 2010, the mother's age distribution correlated with low (4.9%), normal (91.0%), and high birth weights (3.6%): an increase in mother's age resulted in an increase in the frequency of low birth weight infants (LBWIs) and HBWIs.ConclusionThe incidence of HBWIs for the past 50 years has been dropping in Korea. The older the mother, the higher was the risk of a HBWI and LBWI. We hope that these findings would be utilized as basic data that will aid those managing HBWIs.

Small-for-Gestational-Age Births in Pregnant Women with HIV, due to Severity of HIV Disease, Not Antiretroviral Therapy

Objectives. To determine rate and factors associated with small-for-gestational-age (SGA) births to women with HIV. Methods. Prospective data were collected from 183 pregnant women with HIV in an urban HIV prenatal clinic, 2000–2011. An SGA birth was defined as less than the 10th or 3rd percentile of birth weight distribution based upon cut points developed using national vital record data. Bivariate analysis utilized chi-squared and t-tests, and multiple logistic regression analyses were used. Results. The prevalence of SGA was 31.2% at the 10th and 12.6% at the 3rd percentile. SGA at the 10th (OR 2.77; 95% CI, 1.28–5.97) and 3rd (OR 3.64; 95% CI, 1.12–11.76) percentiles was associated with cigarette smoking. Women with CD4 count >200 cells/mm3 at the first prenatal visit were less likely to have an SGA birth at the 3rd percentile (OR 0.29; 95% CI, 0.10–0.86). Women taking NNRTI were less likely to have an SGA infant at the 10th (OR 0.28; 95% CI, 0.10–0.75) and 3rd (OR 0.16; 95% CI, 0.03–0.91) percentiles compared to those women on PIs. Conclusions. In this cohort with high rates of SGA, severity of HIV disease, not ART, was associated with SGA births after adjusting for sociodemographic, medication, and disease severity.

Leisure-Time Physical Activity in Pregnancy and the Birth Weight Distribution: Where Is the Effect?

Leisure-time physical activity (LTPA) is recommended during pregnancy and has been associated with lower risk of delivering a large infant. We sought to characterize the effect of LTPA across the entire birth weight distribution. Women enrolled in the Pregnancy Outcomes and Community Health (POUCH) Study (1998-2004) were followed-up in 2007. Follow-up efforts were extensive for a subcohort and minimal for the remainder (nonsubcohort). Thus, 596 subcohort and 418 nonsubcohort women who delivered at term participated. Offspring were categorized as small-, appropriate-, or large-for-gestational-age (SGA, AGA, and LGA, respectively) based on gender and gestational age-specific birth weight z-scores (BWz). At follow-up, women recalled pregnancy LTPA and were classified as inactive, insufficiently active or meeting LTPA recommendations. Linear, logistic, and quantile regression analyses were conducted separately by subcohort status. Meeting LTPA recommendations decreased odds of LGA significantly among the nonsubcohort (aOR = 0.30, 95% CI: 0.14-0.64) and nonsignificantly among the subcohort (aOR = 0.68, 95% CI: 0.34-1.34). In quantile regression, meeting LTPA recommendations reduced BWz among the upper quantiles in the nonsubcohort. LTPA during pregnancy lowered odds of LGA and reduced BWz among the upper quantiles, without shifting the entire distribution. LTPA during pregnancy may be useful for reducing risks of large fetal size.

Challenges in defining and classifying the preterm birth syndrome

In 2009, the Global Alliance to Prevent Prematurity and Stillbirth Conference charged the authors to propose a new comprehensive, consistent, and uniform classification system for preterm birth. This first article reviews issues related to measurement of gestational age, clinical vs etiologic phenotypes, inclusion vs exclusion of multifetal and stillborn infants, and separation vs combination of pathways to preterm birth. The second article proposes answers to the questions raised here, and the third demonstrates how the proposed system might work in practice.

P2-510 Gestational and neonatal outcomes in teenage pregnancies

IntroductionAccording to the UK government, social exclusion increases the risk of teenage pregnancy and educational factors may be dimensions of such exclusion. In Brazil, around 700 000 girls (32 000...

Mexican American birthweight and child overweight: unraveling a possible early life course health transition.

Mexican American children have a weight distribution that categorizes them as relatively healthy at birth but relatively unhealthy by age 3. This early life course transition in health based on weight raises the question of whether Mexican American children "outgrow" the epidemiologic paradox of favorable birth outcomes despite social disadvantage or whether their birthweight distribution places them on trajectory for overweight in childhood. We address this question using newly available 9-year follow-up data from the Fragile Families and Child Wellbeing birth cohort study linked to pre-natal medical records. We systematically investigate the roles of birthweight, pre-natal factors, and childhood factors in explaining racial/ethnic differences in childhood overweight. Our main finding is that Mexican American children do outgrow the paradox: Their rates of childhood overweight are higher than expected given their birthweight distribution. Observed pre-natal and childhood factors do not explain the elevated rates of overweight among Mexican American children.

Does access to fast food lead to super-sized pregnant women and whopper babies?

Rise in the availability of fast-food restaurants has been blamed, at least partly, for the increasing obesity in the U.S. The existing studies of obesity have focused primarily on children, adolescents, and adults, and this paper extends the literature by raising a little-studied question and using nationally representative data to answer it. It examines the relationship between the supply of fast-food restaurants and weight gain of pregnant women and their newborns. I study prenatal weight gain because excessive weight gain has been linked to postpartum overweight/obesity and I study both tails of the birthweight distribution because the origin of obesity may be traced to the prenatal period and both tail outcomes have been associated with obesity later in life. I merge the 1998 and 2004 Natality Detail Files with the Area Resource File, and County Business Patterns, which provide data on the number of fast-food restaurants in the metropolitan area where the mother resides. The empirical model includes an extensive list of MSA characteristics and MSA fixed effects to control for factors that may be correlated with both health outcomes and restaurants’ location decision. Results reveal that the fast-food and weight gain relationship is robust to the inclusion of these controls but these controls greatly mitigate the fast food–infant health relationship. Greater access to fast-food restaurants is positively related to mothers’ probability of excessive weight gain but it does not share a statistically significant relationship with birthweight. These relationships hold in all the socioeconomic and demographic subgroups studied.

Parental job loss and infant health

This paper is the first to explore the extent to which the health effects of job displacement extend to the children of displaced workers. Using detailed work and fertility histories from the Panel Study of Income Dynamics, estimates are identified by comparing the outcomes of children born after a displacement to the outcomes of those born before. This analysis reveals that husbands’ job losses have significant negative effects on infant health. They reduce birth weights by approximately four and a half percent with suggestive evidence that the effect is concentrated on the lower half of the birth weight distribution.

Advanced parental ages and low birth weight in autism spectrum disorders—Rates and effect on functioning

Objectives (1) To assess the distribution of parental age and birth weight in a large cohort with autism spectrum disorder (ASD) and to compare them to Israeli national data. (2) To examine possible relationships between these risk factors and functioning. Methods The study included 529 participants diagnosed with ASD using standardized tests: the Autism Diagnosis Interview-Revised and the Autism Diagnosis Observation Schedule (ADOS). Medical, developmental and familial histories (gender, age, pregnancy and birth information, parental ages) were obtained. Autism severity was assessed using the new ADOS severity scale and adaptive skill using the Vineland Adaptive Behavior Scales. Results Advanced parental age was associated with ASD. In the older age range the percentages of mothers (35–44 y) and fathers (30–40 y) were significantly higher in the ASD cohort in comparison to the Israeli newborn data. The ASD cohort had significantly higher percentages of low birth weight (<2500 g) and very low birth weight (VLBW < 1500 g) in comparison to the Israeli newborn data. Of these risk factors, only VLBW was associated with lower adaptive functioning. The group with VLBW had lower scores in daily living, socialization and motor skills in comparison to the >1500 g group. Autism severity was not associated with advanced parental age or VLBW. Conclusions The shift in parental age distribution and birth weight in our ASD cohort suggests that the increase in ASD prevalence in recent years might be associated with novel prenatal insults. An adverse fetal course resulting in VLBW may represent a “second hit” phenomenon, causing a poorer outcome.

Distribution of Birth Weight for Gestational Age in Japanese Infants Delivered by Cesarean Section

BackgroundNeonatal anthropometric charts of the distribution of measurements, mainly birth weight, taken at different gestational ages are widely used by obstetricians and pediatricians. However, the relationship between delivery mode and neonatal anthropometric data has not been investigated in Japan or other countries.MethodsThe subjects were selected from the registration database of the Japan Society of Obstetrics and Gynecology (2003–2005). Tenth centile, median, and 90th centile of birth weight by sex, birth order, and delivery mode were observed by gestational age from 22 to 42 weeks among eligible singleton births.ResultsAfter excluding 248 outliers and 5243 births that did not satisfy the inclusion criteria, 144 980 births were included in the analysis. The distribution of 10th centile curves was skewed toward lower birth weights during the preterm period among both first live births and second and later live births delivered by cesarean section. More than 40% of both male and female live births were delivered by cesarean section at 37 weeks or earlier.ConclusionsThe large proportion of cesarean sections influenced the skewness of the birth weight distribution in the preterm period.

Characterizing Components in a Mixture Model for Birthweight Distribution

Low birthweight (LBW) is a well-known risk factor for infant mortality worldwide. Although infant mortality has decreased in the United States during the past 20 years, the incidence of LBW has increased, suggesting that further reductions in infant mortality may be possible if the incidence of LBW can be reduced. In the present work, we introduce a new analytic framework for revealing the relationships between latent variables representing components in a mixture model for birthweight distribution and various other risk factors. More specifically, we show how to estimate the probability that a risk factor is present within one of the mixture components as well as the probability of mixture component membership among infants for whom a risk factor is present, both at a fixed birthweight and averaged across birthweights. We illustrate our analytic framework using publicly available data for white singletons born in the United States between 1998 and 2002. This framework provides a quantitative approach for the prediction of how addressing a modifiable risk factor may affect both the incidence of LBW and infant mortality, thereby facilitating decision making regarding resource allocation toward addressing that risk factor.

Racial disparities in infant mortality: what has birth weight got to do with it and how large is it?

BackgroundIt has been hypothesized that birth weight is not on the causal pathway to infant mortality, at least among "normal" births (i.e. those located in the central part of the birth weight distribution), and that US racial disparities (African American versus European American) may be underestimated. Here these hypotheses are tested by examining the role of birth weight on racial disparities in infant mortality.MethodsA two-component Covariate Density Defined mixture of logistic regressions model is used to decompose racial disparities, 1) into disparities due to "normal" versus "compromised" components of the birth cohort, and 2) further decompose these components into indirect effects, which are associated with birth weight, versus direct effects, which are independent of birth weight.ResultsThe results indicate that a direct effect is responsible for the racial disparity in mortality among "normal" births. No indirect effect of birth weight is observed despite significant disparities in birth weight. Among "compromised" births, an indirect effect is responsible for the disparity, which is consistent with disparities in birth weight. However, there is also a direct effect among "compromised" births that reduces the racial disparity in mortality. This direct effect is responsible for the "pediatric paradox" and maybe due to differential fetal loss. Model-based adjustment for this effect indicates that racial disparities corrected for fetal loss could be as high as 3 or 4 fold. This estimate is higher than the observed racial disparities in infant mortality (2.1 for both sexes).ConclusionsThe results support the hypothesis that birth weight is not on the causal pathway to infant mortality among "normal" births, although birth weight could play a role among "compromised" births. The overall size of the US racial disparities in infant mortality maybe considerably underestimated in the observed data possibly due to racial disparities in fetal loss.

Do Premature Female Infants Really Do Better Than Their Male Counterparts?

We compared survival and outcomes in process of care in female versus male infants born ≤32 weeks gestational age (GA). Data were obtained from the Alere database for infants born ≤32 weeks GA. Females were compared with males for demographics, complications, and care processes. Univariate and multivariate analysis was conducted using chi-square analysis, analysis of variance, or logistic regression. Of the infants included, 6086 female and 6721 males were included. Mean GA did not differ, males were born larger than females, and females were more likely to be born SGA. Males received more surfactant, developed more CLD, received more steroids, and more often required oxygen at discharge. Females were more likely to develop a patent ductus arteriosus. After controlling for body weight, GA, and small-for-GA status, females were more likely to survive (95.4% versus 93.6%, odds ratio 1.63, P < 0.01). Male sex did not play a role in other processes of care except for weaning to a crib. Male infants born ≤32 weeks GA have a decreased rate of survival and an increased rate of respiratory morbidity in spite of higher birth weight distributions. Sex did not play a role in other processes of care.

Birth Outcomes Among Offspring of Women Exposed to the September 11, 2001, Terrorist Attacks

To evaluate the effects of the September 11, 2001, World Trade Center attacks on birth outcomes. Live singleton births between September 11, 2001, and October 31, 2002, to women enrolled in a World Trade Center Health Registry (the Registry, n=446) were compared with births to women residing more than 5 miles from the World Trade Center (n=49,616). Birth weight, gestational age, low birth weight, and preterm delivery were evaluated using linear and logistic regression. Births before September 11, 2001, were analyzed to assess possible seasonal biases of associations with pregnancy trimester on September 11. Associations of birth outcomes with September 11-related psychologic stress and physical exposures were assessed among births to women within the Registry (n=499). Birth weight and gestational age distributions were similar for births to women enrolled in the Registry and comparison births. Although mean gestational age and birth weight varied with trimester on September 11, a similar association was found among births in previous years, consistent with a seasonal effect not related to exposure. Registry-linked births to mothers with probable posttraumatic stress disorder (n=61) had a higher odds of low birth weight (adjusted odds ratio [OR] 2.49, 95% confidence interval [CI] 1.02-6.08) and preterm delivery (adjusted OR 2.48, 95% CI 1.05-5.84) compared with births to women without posttraumatic stress disorder. Women who lived, worked, or were near the World Trade Center on or soon after September 11 had pregnancy outcomes similar to women residing more than 5 miles away. However, among exposed women, probable posttraumatic stress disorder was associated with low birth weight and preterm delivery. II.

Neonatal Anthropometric Charts: The Italian Neonatal Study Compared With Other European Studies

This was a nationwide prospective study carried out in Italy between 2005 and 2007, involving 34 centers with a neonatal intensive care unit. The study reports the Italian Neonatal Study charts for weight, length, and head circumference of singletons born between 23 and 42 gestational weeks, comparing them with previous Italian data and with the most recent data from European countries. Single live born babies with ultrasound assessment of gestational age within the first trimester, and with both parents of Italian origin. Only fetal hydrops and major congenital anomalies diagnosed at birth were excluded. The reference set consists of 22,087 girls and 23,375 boys. At each gestational age, boys are heavier than girls by about 4%. Later-born neonates are heavier than firstborn neonates by about 3%. The effects of sex and birth order on length and head circumference are milder. No differences were observed between babies born in central-north Italy and southern Italy. A large variability emerged among European neonatal charts, resulting in huge differences in the percentage of Italian Neonatal Study neonates below the 10th centile, which is traditionally used to define small-for-gestational-age babies. In the last 2 decades prominent changes in the distribution of birth weight emerged in Italy and in the rest of Europe, in both term and preterm neonates. The existing European neonatal charts, based on more or less recent data, were found to be inappropriate for Italy. Until an international standard is developed, the use of national updated reference charts is recommended.

Thinking outside the curve, part II: modeling fetal-infant mortality.

BackgroundGreater epidemiologic understanding of the relationships among fetal-infant mortality and its prognostic factors, including birthweight, could have vast public health implications. A key step toward that understanding is a realistic and tractable framework for analyzing birthweight distributions and fetal-infant mortality. The present paper is the second of a two-part series that introduces such a framework.MethodsWe propose estimating birthweight-specific mortality within each component of a normal mixture model representing a birthweight distribution, the number of components having been determined from the data rather than fixed a priori.ResultsWe address a number of methodological issues related to our proposal, including the construction of confidence intervals for mortality risk at any given birthweight within a component, for odds ratios comparing mortality within two different components from the same population, and for odds ratios comparing mortality within analogous components from two different populations. As an illustration we find that, for a population of white singleton infants, the odds of mortality at 3000 g are an estimated 4.15 times as large in component 2 of a 4-component normal mixture model as in component 4 (95% confidence interval, 2.04 to 8.43). We also outline an extension of our framework through which covariates could be probabilistically related to mixture components. This extension might allow the assertion of approximate correspondences between mixture components and identifiable subpopulations.ConclusionsThe framework developed in this paper does not require infants from compromised pregnancies to share a common birthweight-specific mortality curve, much less assume the existence of an interval of birthweights over which all infants have the same curve. Hence, the present framework can reveal heterogeneity in mortality that is undetectable via a contaminated normal model or a 2-component normal mixture model.

Thinking outside the curve, part I: modeling birthweight distribution.

BackgroundGreater epidemiologic understanding of the relationships among fetal-infant mortality and its prognostic factors, including birthweight, could have vast public health implications. A key step toward that understanding is a realistic and tractable framework for analyzing birthweight distributions and fetal-infant mortality. The present paper is the first of a two-part series that introduces such a framework.MethodsWe propose describing a birthweight distribution via a normal mixture model in which the number of components is determined from the data using a model selection criterion rather than fixed a priori.ResultsWe address a number of methodological issues, including how the number of components selected depends on the sample size, how the choice of model selection criterion influences the results, and how estimates of mixture model parameters based on multiple samples from the same population can be combined to produce confidence intervals. As an illustration, we find that a 4-component normal mixture model reasonably describes the birthweight distribution for a population of white singleton infants born to heavily smoking mothers. We also compare this 4-component normal mixture model to two competitors from the existing literature: a contaminated normal model and a 2-component normal mixture model. In a second illustration, we discover that a 6-component normal mixture model may be more appropriate than a 4-component normal mixture model for a general population of black singletons.ConclusionsThe framework developed in this paper avoids assuming the existence of an interval of birthweights over which there are no compromised pregnancies and does not constrain birthweights within compromised pregnancies to be normally distributed. Thus, the present framework can reveal heterogeneity in birthweight that is undetectable via a contaminated normal model or a 2-component normal mixture model.

Ambient air pollution exposure and full-term birth weight in California

BackgroundStudies have identified relationships between air pollution and birth weight, but have been inconsistent in identifying individual pollutants inversely associated with birth weight or elucidating susceptibility of the fetus by trimester of exposure. We examined effects of prenatal ambient pollution exposure on average birth weight and risk of low birth weight in full-term births.MethodsWe estimated average ambient air pollutant concentrations throughout pregnancy in the neighborhoods of women who delivered term singleton live births between 1996 and 2006 in California. We adjusted effect estimates of air pollutants on birth weight for infant characteristics, maternal characteristics, neighborhood socioeconomic factors, and year and season of birth.Results3,545,177 singleton births had monitoring for at least one air pollutant within a 10 km radius of the tract or ZIP Code of the mother's residence. In multivariate models, pollutants were associated with decreased birth weight; -5.4 grams (95% confidence interval -6.8 g, -4.1 g) per ppm carbon monoxide, -9.0 g (-9.6 g, -8.4 g) per pphm nitrogen dioxide, -5.7 g (-6.6 g, -4.9 g) per pphm ozone, -7.7 g (-7.9 g, -6.6 g) per 10 μg/m3 particulate matter under 10 μm, -12.8 g (-14.3 g, -11.3 g) per 10 μg/m3 particulate matter under 2.5 μm, and -9.3 g (-10.7 g, -7.9 g) per 10 μg/m3 of coarse particulate matter. With the exception of carbon monoxide, estimates were largely unchanged after controlling for co-pollutants. Effect estimates for the third trimester largely reflect the results seen from full pregnancy exposure estimates; greater variation in results is seen in effect estimates specific to the first and second trimesters.ConclusionsThis study indicates that maternal exposure to ambient air pollution results in modestly lower infant birth weight. A small decline in birth weight is unlikely to have clinical relevance for individual infants, and there is debate about whether a small shift in the population distribution of birth weight has broader health implications. However, the ubiquity of air pollution exposures, the responsiveness of pollutant levels to regulation, and the fact that the highest pollution levels in California are lower than those regularly experienced in other countries suggest that precautionary efforts to reduce pollutants may be beneficial for infant health from a population perspective.

The use of covariates to identify records with implausible gestational ages using the birthweight distribution

The objective of this study was to evaluate the usefulness of covariates in identifying birth records with implausible values of gestational age. Birthweight distributions for births with early reported gestational ages are markedly bimodal, suggesting a mixture of two distributions. Most births form a normal-shaped left-hand (primary) distribution and a smaller number form the right-hand (secondary) distribution. The births in the secondary distribution are thought to have gestational age mistakenly reported. Prior work has found that births in the secondary distribution are at higher risk of poor outcomes than those in the primary distribution. Using 2002 US Natality data for gestational ages 26-35 weeks, we fit normal mixture models to birthweight with and without covariates (maternal race, education, parity, age, region of the country, prenatal care initiation) by reported gestational age. Additional models were stratified by infant sex. This approach allowed for the relationship between the covariates and birthweight to differ between the components. Mixture models fit reasonably well for reported gestational ages <33 weeks, but not for later weeks. Counter to the hypothesis, results were similar for models with and without covariates or stratification or both, although stratified models without covariates predicted slightly more girls and slightly fewer boys in the secondary distribution than did the corresponding unstratified models. For reported gestational ages <33 weeks, predictions from the four sets of models were highly correlated and predictions were similar for subgroups defined by the clinical estimates of gestational age and other covariates. For births with reported gestational ages of 29 or more weeks, the proportion in the secondary distribution exceeded 30%, although this varied by maternal characteristics. The use of covariates and stratification complicated model fitting without materially improving identification of implausible gestational age values, supporting inferences from prior studies using data 'cleaned' without consideration of maternal or infant characteristics.