Birthweight Standards Research Articles

Particulate matter exposure during pregnancy is associated with birth weight, but not gestational age, 1962-1992: a cohort study

BackgroundExposure to air pollutants is suggested to adversely affect fetal growth, but the evidence remains inconsistent in relation to specific outcomes and exposure windows.MethodsUsing birth records from the two major maternity hospitals in Newcastle upon Tyne in northern England between 1961 and 1992, we constructed a database of all births to mothers resident within the city. Weekly black smoke exposure levels from routine data recorded at 20 air pollution monitoring stations were obtained and individual exposures were estimated via a two-stage modeling strategy, incorporating temporally and spatially varying covariates. Regression analyses, including 88,679 births, assessed potential associations between exposure to black smoke and birth weight, gestational age and birth weight standardized for gestational age and sex.ResultsSignificant associations were seen between black smoke and both standardized and unstandardized birth weight, but not for gestational age when adjusted for potential confounders. Not all associations were linear. For an increase in whole pregnancy black smoke exposure, from the 1st (7.4 μg/m3) to the 25th (17.2 μg/m3), 50th (33.8 μg/m3), 75th (108.3 μg/m3), and 90th (180.8 μg/m3) percentiles, the adjusted estimated decreases in birth weight were 33 g (SE 1.05), 62 g (1.63), 98 g (2.26) and 109 g (2.44) respectively. A significant interaction was observed between socio-economic deprivation and black smoke on both standardized and unstandardized birth weight with increasing effects of black smoke in reducing birth weight seen with increasing socio-economic disadvantage.ConclusionsThe findings of this study progress the hypothesis that the association between black smoke and birth weight may be mediated through intrauterine growth restriction. The associations between black smoke and birth weight were of the same order of magnitude as those reported for passive smoking. These findings add to the growing evidence of the harmful effects of air pollution on birth outcomes.

Fetal growth and later maternal death, cardiovascular disease and diabetes

Low birthweight of the offspring has been associated with increased risk of early death and ischemic heart disease in the mother. However, other measurements of fetal growth than the basic birthweight are more accurate. We investigated the relation between the standardized birthweight by gestational age and gender and the ponderal index and the mother's subsequent mortality and cardiovascular morbidity. Registry-based retrospective cohort study. Women with a first singleton delivery in Denmark from 1978 to 2007. 782 287 women followed for 14.6 years yielding 11 600 945 person-years. Cox proportional hazard models. The primary exposures were variation in the standardized birthweight and ponderal index. The endpoints were subsequent maternal death, hypertension, ischemic heart disease, stroke, thrombosis, and diabetes mellitus. The risk-profile for the standardized birthweight and subsequent maternal death had a nadir between -0.5 and -1 SD (HR 0.91; 95%CI 0.83-1.00) and increased with decreasing fetal growth peaking at <-3 SD (HR 2.75; 95%CI 2.37-3.19) compared to the median. The risk-profile for subsequent diabetes mellitus by standardized ponderal index had a nadir between +0.5 to +1 SD (HR 0.82; 95%CI 0.76-0.89) rising with increasing fetal growth and peaking at >+3 SD (HR 17.8; 95%CI 15.0-21.0). The risk-profiles for standardized ponderal index paralleled those for birthweight, but with smaller risk estimates. Adjusting for other pregnancy complications diminished the estimates. The fetal growth is a marker of subsequent risk for premature death, cardiovascular disease, and diabetes mellitus in the mother.

Intrauterine Growth and Neuropsychological Performance in Very Low Birth Weight Preschoolers

In this study we examined the association between intrauterine growth, indexed either as a categorical variable or continuous dimension, and neuropsychological outcome, in a very low birth weight (VLBW) sample of 143 preschoolers. When the commonly used split at the 10th percentile rank was applied to classify intrauterine growth restriction (IUGR), we found that the growth restricted group (n = 25) exhibited significantly poorer performance in the global motor domain, but not on any other neuropsychological measure. In contrast, when adequacy of intrauterine growth was indexed by standardized birth weight, a continuous dimension, this early risk factor explained a unique portion of the variance in global cognitive abilities and visuospatial skills, as well as in global, fine, and gross motor skills. These findings are consistent with recent magnetic resonance imaging data disclosing global neurodevelopmental changes in the brains of preterm infants with IUGR. When cases classified with IUGR (<10th percentile) were excluded, the relationship between adequacy of intrauterine growth and global cognitive abilities remained significant despite range restriction. Hence, an association between appropriateness of intrauterine growth and global intellectual outcome may be observed even within the population of VLBW preschoolers with adequate standardized birth weight.

545: Can the addition of customized standards improve the prediction of fetal macrosomia and cesarean delivery for arrested labor?

Customized birth weight standards have been shown to have improved prediction of adverse pregnancy outcomes compared to population based standards. Our purpose was to determine the rate of fetal macrosomia and cesarean delivery (CD) for arrested labor by prenatal ultrasound estimated fetal weight (EFW) utilizing customized standards compared to population-based standards. We additionally sought to estimate the risk of customized newborn weight >90%ile when estimated fetal weight (EFW) between 28-32 weeks gestation was >90%ile by customized versus population based EFW.

Population Standards of Birth Weight Underestimate Fetal Growth Abnormalities in Diabetic Pregnancies

The objective of this study was to compare the frequency of abnormal fetal growth in women with diabetes mellitus (DM) using population-based birth weight (pop BW) percentiles compared with customized birth weight (cust BW) percentiles, which include adjustments for maternal race, parity, height, weight, and fetal sex. The study design comprised a retrospective cohort of singleton DM pregnancies delivered over a 1-year period (June 2007 to May 2008) from a single tertiary care university-based medical center. Inclusion criteria were gestational age >20 weeks at delivery, live birth, and absence of major chromosomal/structural abnormalities. Small for gestational age (SGA), <10th percentile, and large for gestational age (LGA), >90th percentile pregnancies were categorized based on pop BW or cust BW standards. There were significant differences in the rates of SGA (p < 0.004) and LGA (p < 0.001) between cust BW and pop BW methods. When comparing the two methods, pop BW did not identify 13/16 (81%) of SGA and 23/39 (59%) of LGA babies defined by cust BW methods. The use of cust BW calculation in a diabetic population identified a greater percentage of neonates with pathologic fetal growth compared with pop BW standards, suggesting that the population standard may underdiagnose abnormal fetal growth in diabetic pregnancies.

Birth size and adult size in same-sex siblings discordant for fetal growth in the Early Determinants of Adult Health study.

Many studies have reported on relations between birth size and adult size but the findings to date are hard to compare due to the lack of uniform measures across studies. Interpretation of findings is also hampered by potential confounding by ethnic, socioeconomic and family factors. The purpose of this study is to explore these relationships in a comprehensive fashion, with multiple measures of birth size and adult size, using same-sex sibling controls discordant in birth weight to address potential confounding at the family level. Study subjects include pregnant women enrolled during 1959-1966 in the Child Health and Development Study in Oakland, CA and the Boston, MA, and providence, RI, sites of the Collaborative Perinatal Project in New England, currently combined into the New England Family Study. We assessed 392 offspring (mean age 43 years), the great majority as sibships as available. Our analyses confirm the positive association between birth weight and adult length reported in other studies, with a change in adult height of 1.25 cm (95% CI: 0.79 to 1.70 cm) for each quintile change in standardized birth weight. No associations were seen between birth weight and adult fatness for which findings in other studies are highly variable. As adult weight is likely to reflect recent variations in the adult nutritional environment rather than the early environment, it may be more useful for studies of birth size and adult size to focus on adult length rather than weight measures in evaluating the role of early influences on adult health.

Neonatal, Intrauterine or Customised Birth Weight Standards to Predict Cognitive and School Outcomes in Very Preterm Chilren. Data from the Epipage Cohort Study

Background: Being born small for gestational age (SGA) is associated with developmental disabilities but associations may vary depending on the definition of SGA.Aim: To analyse the impact of this definition on the relation between SGA and cognitive or school outcome.Methods: 980 singletons born before 33 weeks in 1997 in France, part of the Epipage study, free of cerebral palsy, were classified SGA when birth weight was < 10th percentile, according to 3 French standards: 1. neonatal standard: nSGA or nAGA; 2. intrauterine standard using Hadlock's formula: fSGA or fAGA; 3. customised standard taking into account maternal characteristics: cSGA or cAGA.Outcomes were cognitive dysfunction at age 5 defined as a score < -1 SD for the term control group (K-ABC battery), and school difficulties at age 8.Results: 149 children were nSGA (15.2 %), 368 fSGA (37.6 %) and 378 (38.6 %) cSGA. All nSGA children were fSGA and cSGA. Cognitive dysfunction was present in 300 children (35.0 %) and school difficulties in 173 (25.1 %). Children nAGA/fSGA did not have a significant increase of cognitive dysfunction compared to children nAGA/fAGA. Compared to children nAGA/fAGA, children nSGA/fSGA had an adjusted OR of school difficulties of 2.48 [1.52;4.05] while it was 1.63 [1.05;2.55] for children nAGA/fSGA. Children fAGA/cSGA (N=18) had a higher rate of school difficulties compared to children fAGA/cAGA (p=0.03).Conclusions: Intratuerine standard for birth weight is more appropriate than neonatal one to predict school outcome for very preterm singletons. The utility of customisation should be clarified.

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.

The relation of maternal job strain and cortisol levels during early pregnancy with body composition later in the 5-year-old child: The ABCD study

BackgroundPrenatal exposure to maternal stress may program the fetal HPA axis, potentially leading to altered metabolism in later life, associated with adiposity and diabetes. AimsThis association is little studied in humans, and thus we explore whether high maternal job strain during early pregnancy, as well as maternal cortisol levels are associated with increased body mass index (BMI), central adiposity or body fat mass in the offspring at age five. Additionally, we explore whether these associations are modified by gender or mediated by gestational age and fetal growth restriction. Study design2939 pregnant women (ABCD cohort study) completed a questionnaire around gestational week 16 including the Job Content Questionnaire, assessing job strain. Serum total cortisol was assessed in a subsample (n=1320). Gestational age (≥37weeks), standardized birth weight and information on many covariates were available. At the age five health check, height, weight (BMI, kg/m2), waist circumference (waist-to-height ratio, WHtR) and Fat Mass Index (FMI, kg/m2) were assessed. ResultsJob strain was not associated with higher BMI, WHtR or FMI. Higher maternal cortisol was independently associated with marginally higher FMI in girls, but marginally lower FMI in boys (β 0.09 and β −0.10 per 100 unit increase in serum cortisol, respectively. p<0.01). This association was not mediated by gestational age or fetal growth restriction. ConclusionsResults show that prenatal maternal job strain and cortisol may not program obesity and adiposity in the next generation in humans, but gender differences should always be considered.

Lifecourse predictors of mammographic density: the Newcastle Thousand Families cohort Study

Dense mammographic patterns are a strong predictor of breast cancer risk. Factors at differing stages of life have been linked to breast cancer risk, although rarely studied simultaneously. We aimed to investigate whether birth weight and factors later in life were associated with mammographic density in the Newcastle Thousand Families Study. The Study originally consisted of all 1142 babies born in May and June 1947 to mothers resident in Newcastle upon Tyne in Northern England. Detailed information was collected prospectively during childhood, including birth weight and socio-economic circumstances. At age 49-51 years, 574 study members completed a 'Health and Lifestyle' questionnaire. Of the 307 surviving women who returned these questionnaires, 199 returned a further questionnaire asking for details of routine mammographic screening, their reproductive and contraceptive history. Mammographic patterns were coded into Wolfe categories. This was analysed, by ordinal logistic regression, in relation to a range of variables at different stages of life. Increased standardised birth weight (odds ratio, OR 1.32 (95% CI 1.02-1.71) P = 0.03) was a significant independent predictor of higher density. Increasing body mass index (BMI) was predictive of lower density (OR 0.86 per Kg/m(2) (95% CI 0.81-0.92) P < 0.001), as was having reached menopause (OR, compared to pre- and peri-menopausal, 0.41 (95% CI 0.23-0.73) P = 0.002). Interactions were seen between menopausal status and both BMI and age at menarche (P = 0.06) on density, although for neither did the direction of association change. After adjustment for factors acting throughout life, we identified a significant association between standardised birth weight and density in adulthood, consistent with previous research suggesting that heavier babies have an increased risk of breast cancer in later life. We also confirmed associations between both BMI and menopausal status.

Fetal growth and birthweight standards as screening tools: methods for evaluating performance

To discuss different methods for evaluating fetal growth and population-based birthweight standards relevant to different uses: either in antenatal care or in epidemiology. Population-based cohort study. Routinely collected data in Scotland. A total of 540,849 singletons born after 24 weeks between 1980 and 2003. The performance of a fetal growth standard and a population-based birthweight standard are compared in two ways. First, we consider the accuracy of estimated risks of stillbirth at any point during the remaining pregnancy, a measure that is relevant in antenatal care. Second, the rates of stillbirth at each gestation, which are measures relevant in epidemiology, are compared with the actual rates. Standard measures of screening and diagnostic performance: sensitivity, specificity, and positive and negative predictive values. In clinical care, the evidence points towards using fetal growth standards: sensitivity at term is about 30%, increasing to 43% for preterm births (24-31 weeks of gestation), compared with about 29% across all ages under the birthweight standard. Positive predictive values are about 1% across gestations. For epidemiology, the evidence is not so clear-cut: preterm, the population birthweight standard has higher sensitivity and specificity, but this is not the case in the full-term weeks. The performance of fetal growth and birthweight standards should be evaluated in different ways, depending on whether they are intended for use in antenatal care or in epidemiological investigations.

Birthweight Centile Charts for South Asian Infants Born in the UK

Background: UK-born infants of South Asian ethnic origin are known to have lower birthweights than their White British counterparts. When plotted on currently used birthweight charts they can be misclassified as small for gestational age. Similarly, large for gestational age infants can be missed. This has important clinical implications in their management. Objective: To create birthweight centile charts for the UK-born South Asian infants to identify true small and large for gestational age infants. Methods: A retrospective cross-sectional analysis of infants born 1 January 2003 to 31 December 2006 was undertaken. The birthweights of the South Asian and White British infants were compared. The LMS method was used to construct centile charts for the South Asian infants. Results: 24,274 White British and 7,190South Asian infants were included in the analysis. Overall, the South Asian males were 9–15% lighter than the White British males and the South Asian females were 9–13% lighter than the White British females. At term, the median birthweight for South Asian males was 329 g lower than that for White British males and for South Asian females 295 g less than the White British females. Conclusion: There are significant differences in the birthweights of White British and UK-born South Asian infants. Hence the standard birthweight centile charts which were designed using the birthweight data of White British infants appear to misclassify a proportion of South Asian infants. Use of ethnic specific birthweight charts would allow better detection of truly growth-restricted and macrosomic South Asian infants.

The relatively small contribution of birth weight to blood pressure at age 49–51 years in the Newcastle Thousand Families Study

Whereas a large number of previous studies suggest an association between birth weight and later blood pressure, others do not. Controversy surrounds the relative importance of these associations, in particular in relation to more modifiable factors in later life. The aim of this study was to investigate the relative contributions of a range of factors from across life to variations in SBP and DBP in the Newcastle Thousand Families Study. Detailed information was collected prospectively during childhood, including birth weight, duration breast fed and socioeconomic conditions. At age 49-51 years, 574 study members returned self-completion questionnaires and 412 underwent clinical examination, including measurement of DBP and SBP. These data were analysed using linear regression and path analyses. After adjustment for all other significant variables, decreased birth weight, standardized for sex and gestational age (P = 0.035), increased BMI (P < 0.001) and being male (P = 0.034) were independently associated with raised SBP and DBP. Social class at birth (P = 0.044) was also independently associated with DBP. BMI was found to be the most important predictor, with a small relative contribution of standardized birth weight. Adult blood pressure is influenced by numerous factors, acting both directly and indirectly during an individual's lifetime. Inverse associations of standardized birth weight, although statistically significant, were of relatively small importance, with the majority of variation being explained by more modifiable factors in adulthood, in particular adult BMI.

Primiparity at Very Advanced Maternal Age (≥45 years)

This study describes maternal and birth outcomes of primiparae aged ≥ 45. High rates of pregnancy complications and poor birth outcomes were found, stressing that the personal risks and ramifications to the health system should be taken into account in establishing obstetric health policy regarding primiparity at advanced maternal age.

Approximately one-third of medically indicated late preterm births are complicated by fetal growth restriction

The purpose of this study was to report the frequency of fetal growth restriction (FGR) based on indication for late preterm birth (LPTB). Singleton live born pregnancies that were delivered from 34-36 weeks 6 days of gestation over a 1-year period at a tertiary care medical center were studied. Indications for delivery were categorized as spontaneous (spontaneous preterm birth or premature rupture of membranes), medically indicated, or elective. A customized birthweight percentile was calculated for each pregnancy; the rate of FGR was compared based on indication for LPTB. There were 482 LPTBs that met all criteria. Customized birthweight percentiles (median; interquartile range) were different among groups (spontaneous, 45.5%; 20.8-73.5%; medically indicated, 26.9%; 4.1-63.6%; elective, 45.9%; 22.2-78.3%; P = .001). The rate of FGR was also different among groups (spontaneous, 13%; medically indicated, 32%; elective, 21%; P = .001). With the use of customized birthweight standards, we found that FGR complicated approximately one-third of all cases of medically indicated LPTB.

A hospital-based birth weight analysis using computerized perinatal data base for a Chinese population

Objectives. We aimed to construct birth weight-for-gestational age nomograms based on a computerized perinatal data base in a hospital-based Chinese population.Methods. Retrospectively collected 28,052 singleton deliveries at Women and Children's Medical Center, Guangzhou, China. Standard curves of birth weight from 27 to 43 week's gestation were computed. The nomograms included the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles and standard deviations.Results. 79.9% pregnant women delivered between 38, 39, and 40 gestational week, and the mean birth weights are 3160, 3282, and 3388 g, respectively. Preterm birth is 5.7%. In general, male birth weights are greater than females at each gestational week. The hospital-based Chinese population birth weight is lower than that of North American and Scandinavian population.Conclusions. A different standard birth weight is needed for different population. A hospital-based birth weight curve by gestational week is established, which can be a useful tool to estimate intrauterine fetal growth to define SGA or LGA fetuses.

Birth weight and early socio‐economic disadvantage as predictors of sex hormones and sex hormone binding globulin in men at age 49–51 years

A number of associations have been shown between early growth and later sex hormone levels in women, but less is known about this relationship in men. This study investigated life-course predictors of sex hormones in men in the Newcastle Thousand Families birth cohort. The Newcastle Thousand Families Study is a prospective study initiated in 1947. At age 49-51 years, 574 study members returned detailed self-completion questionnaires and 412 attended for clinical examination, including 172 men in whom blood samples were taken. Estradiol, follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone, and sex hormone binding globulin (SHBG) were measured. Free testosterone concentrations were also calculated. Social class at birth independently predicted FSH and LH, with higher levels with increasing socioeconomic disadvantage. SHBG was higher with increasing standardized birth weight and lower with increasing contemporary body mass index (BMI). BMI also predicted LH, SHBG, and testosterone. None of the variables included within this analysis were significant predictors of estradiol. No other associations were seen with any of the variables included from across the life-course. Our findings suggest that birth weight may be positively associated with SHBG and early socioeconomic status may be related to FSH and LH in men. These novel findings are independent of contemporary BMI. Given the links between sex hormones, SHBG and disease outcomes such as type II diabetes and osteoporosis, it is possible that sex hormones may play a mediating role in the associations between circumstances in early life and later risk of chronic disease.

Lifecourse predictors of adult fibrinogen levels: The Newcastle Thousand Families Study

BackgroundResearch investigating early life effects on fibrinogen levels in adult life has produced conflicting results. The aim of this study was to examine and quantify the direct and indirect associations between fetal, infancy and adult risk factors and fibrinogen levels, at age 49–51years, using data from the Newcastle Thousand Families Study. MethodsDetailed information was collected prospectively during childhood, including birth weight, duration of being breast fed and socio-economic conditions. At age 49–51years, 574 study members returned self-completion questionnaires and 412 attended for clinical examination, including the measurement of plasma fibrinogen concentrations in 173 men and 221 women. These data were analysed using linear regression and path analyses. ResultsPoorer quality housing conditions at birth (p=0.001), longer duration of being breast fed (p=0.025), lower current body fat percentage (p<0.001), not being a current smoker (p<0.001) and moderate current alcohol consumption (p=0.002) were significant independent predictors of lower plasma fibrinogen concentration at age 49–51years. No association was observed between plasma fibrinogen concentration and standardised birth weight or with time since stopping smoking among former smokers. ConclusionConcentration of plasma fibrinogen in adulthood is influenced by a range of factors from different stages of life. Although birth weight was not a predictor, there were significant associations with housing conditions in early life and duration of being breast fed. Regardless, the strongest predictors were smoking and contemporary percent body fat. Therefore, modification of these factors would be the most likely way to reduce concentrations of plasma fibrinogen in adulthood.

The customised growth potential: an international research tool to study the epidemiology of fetal growth

Customised centiles based on individual fetal growth potential enhance our ability to differentiate between physiological and pathological smallness. A series of studies in different maternity populations has found striking similarities in the way fetal growth varies with maternal and pregnancy related characteristics, and has established the clear advantages of this method over generic, population-based birthweight or fetal weight standards. The method opens up many new avenues for the retrospective study of risk factors and fetal growth. The findings quantify the strength of association between fetal growth restriction and perinatal outcome, and therefore also highlight the clinical imperative to improve antenatal detection of the at-risk fetus. Applied prospectively as customised charts, the concept improves the detection of fetal growth restriction and reduces the need for unnecessary investigations.

The case against customised birthweight standards

Customised birthweight standards are widely recognised to improve the prediction of adverse perinatal outcomes compared with conventional birthweight-for-gestational-age charts. However, their apparent benefits are more likely to have been derived from their incorporation of intrauterine-based (EFW) reference values at preterm ages than their adjustment for maternal characteristics. Although maternal characteristics are able to explain population-level differences in birthweight, they are not strong enough predictors for individual-level prediction of birthweight. With maternal characteristics accounting for only a small per cent of the total factors influencing birthweight, the best estimate of an infant's birthweight remains close to the population average, explaining the ineffectiveness of adjusting for maternal characteristics. Given that customised percentiles are also unable to distinguish between pathological and physiological influences of maternal characteristics on birthweight, customising birthweight percentiles for maternal characteristics has little justification.