Assessing the possible direct effect of birth weight on childhood blood pressure : a sensitivity analysis.

To estimate the possible direct effect of birth weight on blood pressure, it is conventional to condition on the mediator, current weight. Such conditioning can induce bias. Our aim was to assess the potential biasing effect of U, an unmeasured common cause of current weight and blood pressure, on the estimate of the controlled direct effect of birth weight on blood pressure, with the help of sensitivity analyses. We used data from a school-based study conducted in Switzerland in 2005-2006 (n = 3,762; mean age = 12.3 years). A small negative association was observed between birth weight and systolic blood pressure (linear regression coefficient βbw = -0.3 mmHg/kg, 95% confidence interval: -0.9, 0.3). The association was strengthened upon adjustment for current weight (βbw|C = -1.5 mmHg/kg, 95% confidence interval: -2.1, -0.9). Sensitivity analyses revealed that the negative conditional association was explained by U only if U was relatively strongly associated with blood pressure and if there was a large difference in the prevalence of U between low-birth weight and normal-birth weight children. This weakens the hypothesis that the negative relationship between birth weight and blood pressure arises only from collider-stratification bias induced by conditioning on current weight.

Influence of birth weight on gene regulators of lipid metabolism and utilization in subcutaneous adipose tissue and skeletal muscle of neonatal pigs.

Epidemiological studies suggest that low-birth weight infants show poor neonatal growth and increased susceptibility to metabolic syndrome, in particular, obesity and diabetes. Adipose tissue development is regulated by many genes, including members of the peroxisome proliferator-activated receptor (PPAR) and the fatty acid-binding protein (FABP) families. The aim of this study was to determine the influence of birth weight on key adipose and skeletal muscle tissue regulating genes. Piglets from 11 litters were ranked according to birth weight and 3 from each litter assigned to small, normal, or large-birth weight groups. Tissue samples were collected on day 7 or 14. Plasma metabolite concentrations and the expression of PPARG2, PPARA, FABP3, and FABP4 genes were determined in subcutaneous adipose tissue and skeletal muscle. Adipocyte number and area were determined histologically. Expression of FABP3 and 4 was significantly reduced in small and large, compared with normal, piglets in adipose tissue on day 7 and in skeletal muscle on day 14. On day 7, PPARA and PPARG2 were significantly reduced in adipose tissue from small and large piglets. Adipose tissue from small piglets contained more adipocytes than normal or large piglets. Birth weight had no effect on adipose tissue and skeletal muscle lipid content. Low-birth weight is associated with tissue-specific and time-dependent effects on lipid-regulating genes as well as morphological changes in adipose tissue. It remains to be seen whether these developmental changes alter an individual's susceptibility to metabolic syndrome.

Glomerular number and size in autopsy kidneys: The relationship to birth weight

Background. In the Southeast United States, African Americans have an estimated incidence of hypertension and end-stage renal disease (ESRD) that is five times greater than Caucasians. Higher rates of low birth weight (LBW) among African Americans is suggested to predispose African Americans to the higher risk, possibly by reducing the number of glomeruli that develop in the kidney. This study investigates the relationships between age, race, gender, total glomerular number (N-glom), mean glomerular volume (V-glom), body surface area (BSA), and birth weight. Methods. Stereologic estimates of N-glom and V-glom were obtained using the physical disector/fractionator combination for autopsy kidneys from 37 African Americans and 19 Caucasians. Results. N-glom was normally distributed and ranged from 227,327 to 1,825,380, an 8.0-fold difference. A direct linear relationship was observed between N-glom and birth weight (r=0.423, P=0.0012) with a regression coefficient that predicted an increase of 257,426 glomeruli per kilogram increase in birth weight (alpha=0.050:0.908). Among adults there was a 4.9-fold range in V-glom , and in adults, V-glom was strongly and inversely correlated with N-glom (r=-0.640, P=0.000002). Adult V-glom showed no significant correlation with BSA for males (r=-0.0150, P=0.936), although it did for females (r=0.606, P=0.022). No racial differences in average N-glom or V-glom were observed. Conclusion. Birth weight is a strong determinant of N-glom and thereby of glomerular size in the postnatal kidney. The findings support the hypothesis that LBW by impairing nephron development is a risk factor for hypertension and ESRD in adulthood.

Does birth weight predict childhood diet in the Avon longitudinal study of parents and children?

Study objective: Low birth weight predicts cardiovascular disease in adulthood, and one possible explanation is that children with lower birth weight consume more fat than those born heavier. Therefore, the objective of this study was to investigate associations between birth weight and childhood diet, and in particular, to test the hypothesis that birth weight is inversely related to total and saturated fat intake. Design: Prospective cohort study. Setting: South west England. Participants: A subgroup of children enrolled in the Avon longitudinal study of parents and children, with data on birth weight and also diet at ages 8, 18, 43 months, and 7 years ( 1152, 998, 848, and 771 children respectively). Main results: Associations between birth weight and diet increased in strength from age 8 to 43 months, but had diminished by age 7 years. Fat, saturated fat, and protein intakes were inversely, and carbohydrate intake was positively associated with birth weight at 43 months of age, after adjusting for age, sex, and energy intake. After adjustment for other confounders, all associations were weakened, although there was still a suggestion of a relation with saturated fat ( -0.48 (95% CI -0.97, 0.02) g/day per 500 g increase in birth weight. Similar patterns were seen in boys and girls separately, and when the sample was restricted to those with complete data at all ages. Conclusions: A small inverse association was found between birth weight and saturated fat intake in children at 43 months of age but this was not present at 7 years of age. This study therefore provides little evidence that birth weight modifies subsequent childhood diet.

Social inequality and perinatal health: comparison of three Brazilian cohorts

The objective of the present study was to estimate and compare social inequality in terms of three indicators, i.e., low birth weight (LBW), preterm birth (PTB) and small for gestational age (SGA) birth, in three birth cohorts. Two cohorts were from the city of Ribeirão Preto, where data were collected for all 6748 live born singletons in 1978/79 and for one third of live born singletons (2846) in 1994. The third cohort consisted of 2443 singletons born in São Luís over a period of one year (1997/98). In Ribeirão Preto, LBW and PTB rates increased in all social strata from 1978/79 to 1994. Social inequalities regarding LBW and PTB disappeared since the increase in these rates was more accelerated in the groups with higher educational level. The percentage of SGA infants increased over the study period. Social inequality regarding SGA birth increased due to a more intense increase in SGA births in the strata with lower schooling. In São Luís, in 1997/98 there was no social inequality in LBW or PTB rates, whereas SGA birth rate was higher in mothers with less schooling. We speculate that the more accelerated increase in medical intervention, especially due to the increase in cesarean sections in the more privileged groups, could be the main factor explaining the unexpected increase in LBW and PTB rates in Ribeirão Preto and the decrease or disappearance of social inequality regarding these perinatal indicators in the two cities.

Housing conditions as a social determinant of low birthweight and preterm low birthweight

OBJECTIVE: To assess the relationship between housing conditions and low birthweight and preterm low birthweight among low-income women. METHODS: A case-control study was conducted with post-partum women living in the city of Rio de Janeiro, Southeast Brazil, in 2003-2005. Two groups of cases, low birthweight (n=96) and preterm low birthweight infants (n=68), were compared against normal weight term controls (n=393). Housing conditions were categorized into three levels: adequate, inadequate, and highly inadequate. Covariates included sociodemographic and anthropometric characteristics, risk behaviors, violence, anxiety, satisfaction during pregnancy, obstetric history and prenatal care. RESULTS: Poor housing conditions was independently associated with low birthweight (inadequate - OR 2.3 [1.1;4.6]; highly inadequate - OR 7.6 [2.1;27.6]) and preterm low birthweight (inadequate - OR 2.2 [1.1;4.3]; highly inadequate - OR 7.6 [2.4;23.9]) and factors associated with outcomes were inadequate prenatal care and previous preterm birth. Low income and low maternal body mass index remained associated with low birthweight. CONCLUSIONS: Poor housing conditions were associated with low birthweight and preterm low birthweight.

Preterm birth, infant weight gain, and childhood asthma risk: A meta-analysis of 147,000 European children

BACKGROUND Preterm birth, low birth weight, and infant catch-up growth seem associated with an increased risk of respiratory diseases in later life, but individual studies showed conflicting results. OBJECTIVES We performed an individual participant data meta-analysis for 147,252 children of 31 birth cohort studies to determine the associations of birth and infant growth characteristics with the risks of preschool wheezing (1-4 years) and school-age asthma (5-10 years). METHODS First, we performed an adjusted 1-stage random-effect meta-analysis to assess the combined associations of gestational age, birth weight, and infant weight gain with childhood asthma. Second, we performed an adjusted 2-stage random-effect meta-analysis to assess the associations of preterm birth (gestational age <37 weeks) and low birth weight (<2500 g) with childhood asthma outcomes. RESULTS Younger gestational age at birth and higher infant weight gain were independently associated with higher risks of preschool wheezing and school-age asthma (P < .05). The inverse associations of birth weight with childhood asthma were explained by gestational age at birth. Compared with term-born children with normal infant weight gain, we observed the highest risks of school-age asthma in children born preterm with high infant weight gain (odds ratio [OR], 4.47; 95% CI, 2.58-7.76). Preterm birth was positively associated with an increased risk of preschool wheezing (pooled odds ratio [pOR], 1.34; 95% CI, 1.25-1.43) and school-age asthma (pOR, 1.40; 95% CI, 1.18-1.67) independent of birth weight. Weaker effect estimates were observed for the associations of low birth weight adjusted for gestational age at birth with preschool wheezing (pOR, 1.10; 95% CI, 1.00-1.21) and school-age asthma (pOR, 1.13; 95% CI, 1.01-1.27). CONCLUSION Younger gestational age at birth and higher infant weight gain were associated with childhood asthma outcomes. The associations of lower birth weight with childhood asthma were largely explained by gestational age at birth.

Ethnic/racial diversity, maternal stress, lactation and very low birthweight infants.

OBJECTIVE: (1) To compare maternal characteristics and psychological stress profile among African-American, Caucasian and Hispanic mothers who delivered very low birthweight infants. (2) To investigate associations between psychosocial factors, frequency of milk expression, skin-to-skin holding (STS), and lactation performance, defined as maternal drive to express milk and milk volume. STUDY DESIGN: Self-reported psychological questionnaires were given every 2 weeks after delivery over 10 weeks. Milk expression frequency, STS, and socioeconomic variables were collected. RESULT: Infant birthweight, education, and milk expression frequency differed between groups. Trait anxiety, depression and parental stress in a neonatal intensive care unit (PSS:NICU) were similar. African-American and Caucasian mothers reported the lowest scores in state anxiety and social desirability, respectively. Maternal drive to express milk, measured by maintenance of milk expression, correlated negatively with parental role alteration (subset of PSS:NICU) and positively with infant birthweight and STS. Milk volume correlated negatively with depression and positively with milk expression frequency and STS. CONCLUSION: Differences between groups were observed for certain psychosocial factors. The response bias to self-reported questionnaires between groups may not provide an accurate profile of maternal psychosocial profile. With different factors correlating with maintenance of milk expression and milk volume, lactation performance can be best enhanced with a multi-faceted intervention program, incorporating parental involvement in infant care, close awareness and management of maternal mental health, and encouragement for frequent milk expression and STS.

The social construction of infant mortality: From grassroots to medicalization

Infant mortality as a problematic situation has been recognized for some 130 years in one form or another. It has undergone various changes in its empirical dimensions relative to whom we study within the population, what we study--low birth-weight vs. pre-term births--and how we study it--whether demographically or medically. An analysis of the process by which the condition was raised by claims makers as an intolerable situation among America's urban residents reveals that demographic and medical data were sparse. Nonetheless, a judgement about the meaning and significance of the condition was made, and that interpretation led to the promulgation of systems to both document and address the condition as it has come to be defined.^ This investigation depicts the historical context and natural history of infant mortality as one of a number of social problems that came to be defined through the interplay among groups and individuals making claims and how their claims came to the public policy agenda as worthy of collective resources--who won, who lost and why. The process of social definition focuses attention on the claims makers and the ways they contrast the meaning, origins and remedies for this troubling condition. The historical context becomes the frame of reference for understanding the actions of the claims makers and the meaning and significance they attached to the problem.^ We purport that "context" provides a closer reality than disjoined "value free" accounts. Context provides the evidence for the definition, who participated in the process, why and by what means.^ The role of women in the definitional process reveals the differences in approaches utilized by the women of the settlement house reform movement and African-American women working at the grass-roots. Much of the work done by these two groups provided options to the problem's remedy; however, their differences paved the way to our current (principally medically-oriented) definition and its inherent limitations. ^

ASSOCIATIONS AND INTERRELATIONSHIPS OF SOCIOECONOMIC STATUS, BEHAVIORAL FACTORS AND BIOLOGICAL FACTORS WITH BIRTH WEIGHT

Although the influences of socioeconomic, behavioral and biological factors on birth weight have been extensively studied, most studies have been limited to clinical populations. This study examines such relationships in a national probability sample, the National Health and Nutrition Examination Survey of 1971-1974. The study sample consisted of 2161 white children and 812 black children, aged 1 to 5 years. Analyses were performed on a subsample consisting of 753 white and 138 black children whose mothers were also selected into the survey. Detailed analyses examined interrelationships among socio-economic, behavioral and biological factors by means of multiple regression and partial correlation procedures in the white population. These analyses were not carried out among blacks because of an observed clustering bias introduced in the black subsample that hampered generalization to the US population.^ The results among the whites indicated that the biological factors of maternal height, maternal weight, maternal size (weight/height('2)), maternal age and sex of child were independently related to birth weight and were also interrelated with socioeconomic factors such as family income, education of the mother and education of the head of the household. The joint effect was significantly associated with birth weight.^ Mothers' dietary practices represented the behavioral factors. Selected nutrients from the mothers' 24-hour dietary recall were used to develop indices of dietary quality. Dietary quality was significantly interrelated with socioeconomic status, biological factors and birth weight.^ The findings of this study suggest that smaller, younger mothers of lower socioeconomic status and female children were significantly associated with lower birth weight. The findings also suggest that dietary quality is a mediating factor among socioeconomic status and biological factors in that mothers with more financial and educational resources have better dietary practices. Such mothers may also practice other health behaviors that would prevent having a low birthweight baby. This dissertation contributes primarily to the further conceptualization and empirical testing of the interrelationships among socioeconomic, behavioral and biological factors with respect to birth weight. ^

Behavioral decision making and the levels of change: An application of the transtheoretical model to prenatal smoking in low -income women

Despite continued research and public health efforts to reduce smoking during pregnancy, prenatal cessation rates in the United States have decreased and the incidence of low birth weight has increased from 1985 to 1991. Lower socioeconomic status women who are at increased risk for poor pregnancy outcomes may be resistant to current intervention efforts during pregnancy. The purpose of this dissertation was to investigate the determinants of continued smoking and quitting among low-income pregnant women.^ Using data from cross-sectional surveys of 323 low-income pregnant smokers, the first study developed and tested measures of the pros and cons of smoking during pregnancy. The original decisional balance measure for smoking was compared with a new measure that added items thought to be more salient to the target population. Confirmatory factor analysis using structural equation modeling showed neither the original nor new measure fit the data adequately. Using behavioral science theory, content from interviews with the population, and statistical evidence, two 7-item scales representing the pros and cons were developed from a portion (n = 215) of the sample and successfully cross-validated on the remainder of the sample (n = 108). Logistic regression found only pros were significantly associated with continued smoking. In a discriminant function analysis, stage of change was significantly associated with pros and cons of smoking.^ The second study examined the structural relationships between psychosocial constructs representing some of the levels of and the pros and cons of smoking. The cross-sectional design mandates that statements made regarding prediction do not prove causation or directionality from the data or methods analysis. Structural equation modeling found the following: more stressors and family criticism were significantly more predictive of negative affect than social support; a bi-directional relationship was found between negative affect and current nicotine addiction; and negative affect, addiction, stressors, and family criticism were significant predictors of pros of smoking.^ The findings imply reversing the trend of decreasing smoking cessation during pregnancy may require supplementing current interventions for this population of pregnant smokers with programs addressing nicotine addiction, negative affect, and other psychosocial factors such as family functioning and stressors. ^

The expression of vulnerability through infant mortality in the municipality of Embu

CONTEXTO E OBJETIVO: A mortalidade infantil expressa uma conjunção de fatores relacionados às condições de vida, trabalho e acesso aos serviços de saúde, e a identificação desses fatores pode contribuir para definição de intervenções em saúde. O objetivo deste trabalho foi analisar a expressão da vulnerabilidade e conseqüentes diferenças de acesso aos serviços de saúde e na ocorrência de óbitos em menores de um ano no município do Embu. TIPO DE ESTUDO E LOCAL: Estudo descritivo, no município de Embu. MÉTODOS: Foram coletados dados secundários (declarações de óbitos) e primários (entrevistas a famílias de crianças residentes do município do Embu, falecidas nos anos de 1996 e 1997, antes de completarem um ano). Variáveis estudadas foram relacionadas às condições de vida, renda e trabalho, à assistência pré-natal, ao parto e à atenção à saúde da criança, as quais foram comparadas com resultados obtidos em estudo realizado no ano de 1996. RESULTADOS: Verificaram-se diferenças estatisticamente significantes quanto a renda, trabalho sem carteira assinada e acesso a plano privado de saúde entre famílias de crianças que foram ao óbito. Verificaram-se, também, diferenças quanto ao acesso e à qualidade da assistência pré-natal, à freqüência de baixo peso ao nascer e a intercorrências neonatais. CONCLUSÕES: A situação de emprego/desemprego foi decisiva na determinação da estabilidade familiar, conferindo maior vulnerabilidade para ocorrência de óbitos infantis, somada às condições de acesso e à qualidade dos serviços de saúde

Common mental disorders during pregnancy: prevalence and associated factors among low-income women in Sao Paulo, Brazil

To estimate the prevalence of common mental disorders (CMD) and factors associated with these disorders among pregnant women of low socio-economic status (SES) in Sao Paulo. We performed a cross-sectional study with 831 women in their 20th to 30th weeks of pregnancy, who were attending antenatal clinics in primary care in Sao Paulo, Brazil. CMD were assessed with the Clinical Interview Schedule-Revised. Crude and adjusted prevalence ratios and 95% CI were calculated to examine the association between CMD and exposure variables. The prevalence of CMD was 20.2% (95% CI 17.5 to 23.0). Age at current pregnancy and at first delivery, current obstetric complications, not having friends in the community, living in a crowded household, lower occupational status and history of previous psychiatric treatment were all independently associated with increased prevalence of CMD. CMD is highly prevalent among pregnant women of low SES seen in primary care settings in Sao Paulo. A combination of distal and proximal psychosocial factors increase the risk for CMD. Primary health care professionals need to be aware of how common CMD in such settings and properly trained to deal with CMD during pregnancy.

Genetic and non-genetic factors affecting birth-weight and adult body mass index

Birthweight affects neonatal mortality and morbidity and has been used as a marker of foetal undernutrition in studies of prenatal effects on adult characteristics. It is potentially influenced by genetic and environmental influences on the mother, and effects of foetal genotype, which is partially derived from the maternal genotype. Interpretations of variation in birthweight and associated characteristics as being due to prenatal environment ignore other possible modes of materno-foetal transmission. Subjects were adult twins recruited through the Australian Twin Registry, aged 17 to 87 years, and the sample comprised 1820 men and 4048 women. Twins reported their own birthweight as part of a health questionnaire. Body Mass Index (BMI) was calculated from self-reports of height and weight. Correlations between co-twins' birthweights were high for both monozygotic (r = 0.77) and dizygotic (r = 0.67) pairs, leading to substantial estimates of shared environmental effects (56% of variance) with significant additive genetic (23%) and non-shared environmental (21%) components. Adult BMI was mainly influenced by genetic factors, both additive (36% of variance) and nonadditive (35%). The correlation between birthweight and BMI was positive, in that heavier babies became on average more obese adults. A bivariate model of birthweight and adult BMI showed significant positive genetic (rg = 0.16, p = 0.005) and environmental (re = 0.08, p = 0.000011) correlations. Intra-uterine environmental or perinatal influences shared by cotwins exercise a strong influence on birthweight, but the factors which affect both birthweight and adult BMI are partly genetic and partly non-shared environmental.