Relative contributions of maternal social and biological characteristics to birth weight and gestation among mothers of different childhood socioeconomic status

There has been no reported systematic attempt to quantify the relative unique contribution of multiple social and biologic maternal characteristics to birthweight and gestational time among mothers of differing childhood socioeconomic backgrounds. This issue was examined in 3 nativity cohorts from a population of 766 black prenatal clinic patients in New York City using a series of stepwise hierarchical multiple regression analyses. Different variable sets contributed to birthweight variance in each group, although total variance explained was similar for the 3. Since the foreign-born cohort represented a different higher childhood socioeconomic background, but was similar to the other groups in current socioeconomic status, the differing observed associations of variable sets to birthweight may be related to childhood socioeconomic status. In all groups, social factors show more effect on gestation among those births more than 2500 grams than for smaller babies and thus account for more total explained birthweight variance for births over 2500 grams. Future research is necessary to replicate these results in the general population since this is the 1st study using multivariate techniques to look at social and biological factors associated with birthweight in groups with different childhood social backgrounds.     

Weight at Birth and Subsequent Fecundability: A Prospective Cohort Study

Objective

To examine the association between a woman''s birth weight and her subsequent fecundability.

Method

In this prospective cohort study, we included 2,773 Danish pregnancy planners enrolled in the internet-based cohort study “Snart-Gravid”, conducted during 2007–2012. Participants were 18–40 years old at study entry, attempting to conceive, and were not receiving fertility treatment. Data on weight at birth were obtained from the Danish Medical Birth Registry and categorized as <2,500 grams, 2,500–2,999 grams, 3,000–3,999 grams, and ≥4,000 grams. In additional analyses, birth weight was categorized according to z-scores for each gestational week at birth. Time-to-pregnancy measured in cycles was used to compute fecundability ratios (FR) and 95% confidence intervals (CI), using a proportional probabilities regression model.

Results

Relative to women with a birth weight of 3,000–3,999 grams, FRs adjusted for gestational age, year of birth, and maternal socio-demographic and medical factors were 0.99 (95% CI: 0.73;1.34), 0.99 (95% CI: 0.87;1.12), and 1.08 (95% CI: 0.94;1.24) for birth weight <2,500 grams, 2,500–2,999 grams, and ≥4,000 grams, respectively. Estimates remained unchanged after further adjustment for markers of the participant''s mother''s fecundability. We obtained similar results when we restricted to women who were born at term, and to women who had attempted to conceive for a maximum of 6 cycles before study entry. Results remained similar when we estimated FRs according to z-scores of birth weight.

Conclusion

Our results indicate that birth weight appears not to be an important determinant of fecundability.     

Influence of variation in birth weight within normal range and within sibships on IQ at age 7 years: cohort study

ObjectiveTo examine the relation between birth weight and measured intelligence at age 7 years in children within the normal range of birth weight and in siblings.DesignCohort study of siblings of the same sex.Setting12 cities in the United States.Subjects3484 children of 1683 mothers in a birth cohort study during the years 1959 through 1966. The sample was restricted to children born at ⩾37 weeks gestation and with birth weights of 1500-3999 g.ResultsMean IQ increased monotonically with birth weight in both sexes across the range of birth weight in a linear regression analysis of one randomly selected sibling per family (n= 1683) with adjustment for maternal age, race, education, socioeconomic status, and birth order. Within same sex sibling pairs, differences in birth weight were directly associated with differences in IQ in boys (812 pairs, predicted IQ difference per 100 g change in birth weight =0.50, 95% confidence interval 0.28 to 0.71) but not girls (871 pairs, 0.10, −0.09 to 0.30). The effect in boys remained after differences in birth order, maternal smoking, and head circumference were adjusted for and in an analysis restricted to children with birth weight ⩾ 2500 g.ConclusionThe increase in childhood IQ with birth weight continues well into the normal birth weight range. For boys this relation holds within same sex sibships and therefore cannot be explained by confounding from family social environment.

What is already known on this topic

IQ at school age is linked to birth weight among low birthweight babiesSome evidence suggests the association might also apply to children of normal birth weight

What this study adds

IQ at age 7 years is linearly related to birth weight among children of normal birth weightThe relation was not due to confounding by maternal or socioeconomic factorsIQ is also associated with differences in birth weight between boy sibling pairs but not girls     

Effects of birth weight on later intelligence

Abstract

Identical twins are used to show the long‐term effects of birth weight when genetic and many environmental factors are controlled. Female twins between the ages of 6 and 10 are evaluated for performance IQ and other measures of activity. No relationship was found between any of these measures and birth weight except for IQ. The heavier cotwin had the higher IQ score even when the birth weight of each twin was above 2,500 grams. Birth order was not associated with intelligence within the twin pairs.     

Effects of Maternal Pregnancy Intention,Depressive Symptoms and Social Support on Risk of Low Birth Weight: A Prospective Study from Southwestern Ethiopia

Background

Low birth weight (LBW) is the principal risk factor for neonatal and infant mortality in developing countries. This study examines the effects of unwanted pregnancy, prenatal depression and social support on the risk of low birth weight in rural southwestern Ethiopia. We hypothesized that unwanted pregnancy and prenatal depression increase the risk of low birth weight, while social support mediates this association.

Methods

Data for the study comes from a prospective study in which women were followed from pregnancy through to delivery. Six hundred twenty two women were followed and 537 birth weights were measured within 72 hours. Multivariable log binomial regression was used to model the risk of low birth weight.

Results

The mean birth weight was 2989 grams (SD±504 grams), and the incidence of LBW was 17.88%. The mean birth weight of babies after unwanted pregnancy was 114 g lower compared to births from intended pregnancy. Similarly, mean birth weight for babies among women with symptoms of antenatal depression was 116 grams lower. Results of unadjusted log-binomial regression showed that unwanted pregnancy, prenatal depression and social support were associated with LBW. The relationship between antenatal depressive symptoms and LBW was mediated by the presence of social support, while the association between LBW and unwanted pregnancy remained after multivariable adjustment.

Conclusion

The incidence of low birth weight is high in the study area. Poverty, nonuse of antenatal care, low social support and unwanted pregnancy contribute to this high incidence of low birth weight. Hence, identifying women’s pregnancy intention during antenatal care visits, and providing appropriate counseling and social support will help improve birth outcomes.     

A partial explanation of superior birth weights among foreign-born women

This study of 766 black women reexamined the issue of advantage in birthweight and length of gestation in foreign-born women and confirms the reported higher birthweights among that group. Subjects were new registrants for prenatal care at a public clinic in Harlem, New York City, 1971-73, and were part of a randomized trial of nutritional supplementation during pregnancy. 3 nativity groups were represented: New York City, southern United States, and foreign countries. Despite the standard selection of all subjects for high risk for low birthweight, foreign-born women had only 3.8% of births under 2500 grams in contrast to 15.6% among the southern women, and 18% among New York City natives. 6 sets of variables were examined in relation to birthweight outcome. An average birthweight advantage of 218 grams for the foreign-born was found to be associated with higher childhood social status and more positive health behaviors.     

Organic-solvent water pollution and low birth weight in Michigan.

This pilot study explored the association between a measure of water pollution caused by benzene or chlorinated solvents and the incidence of low birth weights for white residents of Michigan counties. A positive relationship between water pollution by these contaminants and the per cent of low-weight births (less than 2,500 grams, or about 5.5 pounds) resulted despite controls for the incidence of teenaged childbearing, infrequent prenatal care, and mean household income from wages or salaries. Water pollution showed an association with the incidence of low birth weight that was as strong as that between low birth weight and low prenatal care. While correlation cannot prove causation, the finding suggests that impure water may impair fetal growth in Michigan.     

Influence of birth weight on differences in infant mortality by social class and legitimacy.

OBJECTIVE--To investigate the influence of birth weight on the pronounced social class differences in infant mortality in Britain. DESIGN--Analysis of routine data on births and infant deaths. SETTING--England and Wales. SUBJECTS--All live births and infant deaths, 1983-5. MAIN OUTCOME MEASURE--Mortality in infants by social class, birth weight, and legitimacy according to birth and death certificates. RESULTS--Neonatal and postneonatal mortality (deaths/1000 births) increased with social class. Neonatal and postneonatal mortality was 4.2/1000 and 2.3/1000 respectively for social class I and 6.8/1000 and 5.6/1000 respectively for social class V. Mortality was lower among births registered within marriage (postneonatal 3.5/1000; neonatal 5.2/1000) than among those jointly registered outside marriage (5.1/1000; 6.4/1000); mortality was highest in those solely registered outside marriage (7.2/1000; 7.0/1000). For neonatal mortality the effect of social class varied with birth weight. Social class had little effect on neonatal mortality in low birthweight babies and increasing effect in heavier babies. For postneonatal mortality the effect of social class was similar for all birth weights and was almost as steep as for all birth weights combined. CONCLUSION--Birth weight mediates little of the effect of social class on postneonatal mortality.     

Social status and season of birth: a study of a metropolitan area in the southeastern United States

An analysis of live birth statistics obtained from the Health Department of Fulton County, Georgia for 1967-1977 indicated that seasonal variation in birth was significantly related to maternal social status. Mothers were assigned to social status classification on the basis of whether they lived in an upper, upper middle, lower middle, or lower socioeconomic census tract. Periodic regression analysis and analysis of variance was applied to the data. Specific findings were 1) upper status groups showed no significant variation in births; 2) upper and lower middle classes showed a similar and a significant degree of seasonal variation with depressed birth levels from January-June and elevated levels from July-December; 3) lower class birth patterns showed more seasonal variation than the other classes; 4) the periodic curve accounted for 92.3% of the monthly variation in births for the lower class, 70.6% for the lower middle class, and 64.6% for the upper middle class; 5) the relationship between social status and seasonal variation in births held for both whites and non-whites; 6) seasonal variations were somewhat more marked for non-whites than for white in the lower and lower middle class; and 7) the observed relationship held throughout the 11 year period of observation. The results were of special concern given previous studies which found that children born in September-October entered school on the average earlier than other children and did less well in school than other students. Major findings were presented in graphic and tabular form.     

Birth weight and later socioeconomic disadvantage: evidence from the 1958 British cohort study.

OBJECTIVE--To investigate the relation between birth weight and socioeconomic disadvantage during childhood and adolescence in a birth cohort study. DESIGN--Longitudinal analysis of birth weight in relation to social class, household amenities and overcrowding, and financial difficulties as reported by parents at interview when participants were aged 7, 11, and 16 years; and receipt of unemployment or supplementary benefits as reported by participants at age 23. SUBJECTS--Male participants in the 1958 birth cohort (national child development study) born to parents resident in Great Britain during the week of 3-9 March 1958. Data on birth weight and financial difficulties between birth and 23 years were available for 4321; data on housing conditions and social class at ages 7, 11, and 16 years were available for 3370. MAIN OUTCOME MEASURES--Socioeconomic disadvantage at later ages in men weighing 6 lb (2721g) or under at birth compared with those weighing over 6 lb and between fifths of the distribution of birth weight. RESULTS--Cohort members who weighed 6 lb or under at birth were more likely to experience socioeconomic disadvantage subsequently. Those in lower fifths of the distribution were more likely to experience socioeconomic disadvantage. CONCLUSION--Low birth weight is associated with socioeconomic disadvantage in childhood and adolescence. Studies of the association of indicators of early development and adult disease need to take into account experiences right through from birth to adulthood if they are to elucidate the combination of risks attributable to developmental problems and socioeconomic disadvantage.     

Racial fertility differences: The role of female employment and education in wanted and unwanted childbearing

Abstract

This paper employs data from a merged sample of the National Surveys of Family Growth to examine how female employment status conditions the relationship between education and wanted and unwanted births among African American and white women. A rationale is presented for why a minority group status hypothesis that posits lower fertility among more highly educated African American women as compared to similar white women might find support in the case of wanted births and among certain women, including earlier birth cohorts. Our results provide some evidence for these ideas as well as evidence for a social characteristics hypothesis that predicts convergence of childbearing with rising education. However, persistently higher levels of unwanted births among African American women of all educational levels suggest that the dynamics of racial fertility differences are more complex than either of the hypotheses imply.     

Patterns of low birth weight in the Bengali newborns

This paper examines the distribution of low birth weight (2500 g or less) by gestation time, sex, maternal age, parity (birth order), socioeconomic conditions, and season of birth among 5117 single live births born to Bengali mothers at the Ramakrishna Mission Seva Pratisthan Hospital in Calcutta, India. Preterm infants have low birth weight significantly more often than their full term counterparts. Female infants have low birth weights significantly more often than male infants. The infants of poor mothers have lower birth weights in higher order births more often than infants of higher orders born to well-off mothers. Teenaged mothers produce low birth weight babies significantly more often than older mothers. Although the relationship is not significant, low birth weight infants occur more often among 1st and late born infants and less often among 2nd born infants. The season of birth is not significantly associated with birth weight. Less than 10% of low birth weight infants are pre-term, while the rest are full term. The great majority of low birth weight infants are small-for-gestational-age; the minority are small due to curtailed gestational age. The proportion of infants weighing less than 2001 g is only 9%; this figure tallies closely with earlier studies of India.     

Social class in childhood and general health in adulthood: questionnaire study of contribution of psychological attributes

ObjectiveTo determine the contribution of psychological attributes (personality characteristics and coping styles) to the association between social class in childhood and adult health among men and women.DesignPartly retrospective, partly cross sectional study conducted in the framework of the Dutch GLOBE study.SubjectsSample of general population from south east Netherlands consisting of 2174 men and women aged 25-74 years. Baseline self reported data from 1991 provided information on childhood and adult social class, psychological attributes, and general health.ResultsIndependent of adult social class, low childhood social class was related to self rated poor health (odds ratio 1.67 (95% confidence interval 1.02 to 2.75) for subjects whose fathers were unskilled manual workers versus subjects whose fathers were higher grade professionals). Subjects whose fathers were manual workers generally had more unfavourable personality profiles and more negative coping styles. External locus of control, neuroticism, and the absence of active problem focused coping explained about half of the association between childhood social class and self rated poor health. The findings were independent of adult social class and height.ConclusionsA higher prevalence of negative personality profiles and adverse coping styles in subjects who grew up in lower social classes explains part of the association between social class in childhood and adult health. This finding underlines the importance of psychological mechanisms in the examination of the negative effects of adverse socioeconomic conditions in childhood.

Key messages

• Regardless of adult social class, low social class in childhood is related to poor general health in adulthood
• Adverse personality profiles and negative coping styles are more common in people who grew up in lower social classes
• Psychological attributes, such as low perceived control, explain a substantial part of the direct association between childhood social class and adult health
• Psychological mechanisms may explain adverse health outcomes in adults who have a low socioeconomic background

     

Polygenic and socioeconomic risk for high body mass index: 69 years of follow-up across life

Genetic influences on body mass index (BMI) appear to markedly differ across life, yet existing research is equivocal and limited by a paucity of life course data. We thus used a birth cohort study to investigate differences in association and explained variance in polygenic risk for high BMI across infancy to old age (2–69 years). A secondary aim was to investigate how the association between BMI and a key purported environmental determinant (childhood socioeconomic position) differed across life, and whether this operated independently and/or multiplicatively of genetic influences. Data were from up to 2677 participants in the MRC National Survey of Health and Development, with measured BMI at 12 timepoints from 2–69 years. We used multiple polygenic indices from GWAS of adult and childhood BMI, and investigated their associations with BMI at each age. For polygenic liability to higher adult BMI, the trajectories of effect size (β) and explained variance (R²) diverged: explained variance peaked in early adulthood and plateaued thereafter, while absolute effect sizes increased throughout adulthood. For polygenic liability to higher childhood BMI, explained variance was largest in adolescence and early adulthood; effect sizes were marginally smaller in absolute terms from adolescence to adulthood. All polygenic indices were related to higher variation in BMI; quantile regression analyses showed that effect sizes were sizably larger at the upper end of the BMI distribution. Socioeconomic and polygenic risk for higher BMI across life appear to operate additively; we found little evidence of interaction. Our findings highlight the likely independent influences of polygenic and socioeconomic factors on BMI across life. Despite sizable associations, the BMI variance explained by each plateaued or declined across adulthood while BMI variance itself increased. This is suggestive of the increasing importance of chance (‘non-shared’) environmental influences on BMI across life.     

Lack of an association between ABO and Rh blood group polymorphisms and stature, body weight, and BMI in a cohort of British women

Analysis of variance shows no significant associations between stature, weight, or body mass index (BMI) and ABO or Rh blood group phenotypes among a sample of mothers in England, Scotland, and Wales whose children were born during March 3-9, 1958. Social factors are significantly associated with stature and weight; the effects of social class of the women's fathers, regions of birth of the women, their ages, whether their education continued beyond age 16 or not, and the total number of births were separated out by regression analysis. The adjusted residual regression of ABO and Rh phenotypes were not significantly related to reported stature, weight, or BMI.     

Birth weight correlates differently with cardiovascular risk factors in youth

Objective: Childhood obesity has become prevalent, resulting in a greater risk of hypertension, diabetes, and dyslipidemia. However, the relationship between these comorbid conditions and birth weight remains uncertain. We conducted this study to evaluate the relationship between birth weight and cardiovascular risk factors in children and adolescents. Research Methods and Procedures: In a nationwide survey conducted between 1992 and 2000, all schoolchildren 6 to 18 years old with glucosuria, proteinuria, or microscopic hematuria in repeated urine samples were included and received a physical examination and blood test. Those with gestational age <37 weeks were excluded. We enrolled 81,538 children (51,111 girls and 30,427 boys) and obtained their birth weights from the Taiwan Birth Registry. Obesity and hypertension were defined by age‐ and sex‐specific cut‐offs. Diabetes was diagnosed if the fasting glucose was >7 mM. Results: The risk of obesity was higher for those with birth weights ≥4000 grams [odds ratio (OR), 1.65] and 3543 to 3999 grams (OR, 1.28) and lower for those with birth weights 2601 to 2999 grams (OR, 0.90), using 3000 to 3542 grams as the reference group. An increased risk of diabetes was associated with both higher and lower birth weights, indicating a U‐shaped relationship (OR, <2600 grams, 1.607; 2601 to 2999 grams, 1.119; 3543 to 3999 grams, 1.112; ≥4000 grams, 1.661). In the 10‐ to 12‐year‐old age group, the risk of hypertension was higher in those with birth weights <2600 grams (OR, 1.20). Discussion: Low birth weight was associated with childhood diabetes. High birth weight was correlated with childhood obesity and diabetes. Our data indicate different relationships between birth weight and the development of obesity, hypertension, and diabetes in childhood.     

Size at birth and resilience to effects of poor living conditions in adult life: longitudinal study

ObjectiveTo determine whether men who grew slowly in utero or during infancy are more vulnerable to the later effects of poor living conditions on coronary heart disease.DesignFollow up study of men for whom there were data on body size at birth and growth and social class during childhood, educational level, and social class and income in adult life.SettingHelsinki, Finland.Participants3676 men who were born during 1934-44, attended child welfare clinics in Helsinki, were still resident in Finland in 1971, and for whom data from the 1980 census were available.ResultsMen who had low social class or low household income in adult life had increased rates of coronary heart disease. The hazard ratio among men with the lowest annual income (<£8400) was 1.71 (95% confidence interval 1.18 to 2.48) compared with 1.00 in men with incomes above £15 700. These effects were stronger in men who were thin at birth (ponderal index <26 kg/m³): hazard ratio 2.58 (1.45 to 4.60) for men with lowest annual income. Among the men who were thin at birth the effects of low social class were greater in those who had accelerated weight gain between ages 1 and 12 years. Low social class in childhood further increased risk of disease, partly because it was associated with poor growth during infancy. Low educational attainment was associated with increased risk, and low income had no effect once this was taken into account.ConclusionMen who grow slowly in utero remain biologically different to other men. They are more vulnerable to the effects of low socioeconomic status and low income on coronary heart disease.

What is already known on this topic

People who grow slowly in utero and during infancy remain biologically different through their livesSuch people are at increased risk of coronary heart disease

What this study adds

Among men who were thin at birth the risk of coronary heart disease is further increased if they have poor living standards in adult lifeOther men tend to be resilient to the adverse effects of poor living standards     

Association of birth weight and current body size to blood pressure in female twins.

It has been proposed that low birth weight is associated with high levels of blood pressure in later life. The aim of this study was to assess the relationship of blood pressure to birth weight and current body size during growth and adulthood. A total of 711 female multiple births, with one group of 244 in their growth phase mean age 12.0 (2.3)(SD) years and the other of 467 adults (mean age 35.2 (12.6) years), had height, weight and both systolic (SBP) and diastolic (DBP) blood pressures measured, and self-reported their birth weight. Regression analyses were performed to assess the cross-sectional and within-pair associations of blood pressure to birth weight, with and without adjustments for current body size. Within-pair analysis was based on 296 twin pairs. Cross-sectionally, a reduction in birth weight of 1 kg was associated with 2 to 3 mm Hg higher age-adjusted SBP, which was of marginal significance and explained about 2% of the population variance. Adjustment for body mass index did not significantly change this association. Within-pair analyses found no association between birth weight and SBP or DBP,even after adjusting for current body size. After age, current body size was the strongest predictor of systolic BP. The weak association of blood pressure to birth weight cross-sectionally is of interest, but any within-pair effect of birth weight on blood pressure must be minimal compared with the effect of current body size.     

Deformed nasal septa and relaxed selection

Abstract

Demographic studies undertaken in several Andean countries have found that women residing at high altitudes have significantly fewer live births than do their low altitude counterparts. This reduction has been explained as being due to various factors: the debilitating effects of hypoxia upon the reproductive system; the effects of sociocultural factors which vary with altitude and which affect reproductive behavior; and errors in data collection. In order to examine the validity of some of these hypotheses, the fertility of a group of 906 Bolivian women residing at low, medium, and high altitudes was examined. The women were selected from the lower socioeconomic strata and reported never having used any method of contraception. A detailed analysis of the fertility of these women showed no significant altitude‐related differences in the number of live births. However, as a result of significantly higher childhood mortality rates at altitude, there was a significant reduction in numbers of living children. The results of this study suggest that the collection and analysis of census data that ignores socioeconomic differences within a population or differences among census units in neonatal or early childhood mortality may bias or complicate the study of the impact of altitude on human fertility. Although the present research does not prove that hypoxic stress does not affect the reproductive system, the results suggest that if altitude does reduce fecundity, the reduction is not great and is likely to be shown only through studies of reproductive physiology.