Intergenerational studies of human birthweight from the 1958 birth cohort. II. Do parents who were twins have babies as heavy as those born to singletons?

Pregnancy, smoking and birth outcomes

This review summarizes the epidemiology and consequences of maternal smoking in pregnancy, with emphasis on the adverse effects on birth outcomes. In developed countries, approximately 15%, and in developing countries, approximately 8% of women smoke cigarettes, and adolescents and women from lower socioeconomic groups are more likely than other women to smoke while pregnant. Maternal smoking during pregnancy is the largest modifiable risk factor for intrauterine growth restriction. A meta-analysis of recent studies showed that the pooled estimate for reduction of mean birthweight was 174 g (95% confidence limits 132-220 g). Other studies confirm a weaker association between maternal smoking and preterm birth. The population attributable risk of low birthweight due to maternal smoking in the UK is estimated to be 29-39%. Tobacco smoke toxins damage the placenta and may lead to placental abruption, abortion or placenta praevia. Infants of mothers who smoke in pregnancy are at an increased risk of respiratory complications including asthma, obesity and, possibly, behavioral disorders. These effects may be dose-related, as there is good evidence that mean birthweight decrements are greater with increased numbers of cigarettes smoked during pregnancy. Cotinine is a useful indicator of tobacco smoke exposure in pregnant women and higher levels in body fluids have been related to lower birthweights. Maternal genetic polymorphisms of the cytochrome P (CYP)450 and glutathione-S-transferase (GST) subfamilies of metabolic genes influence the magnitude of the effect of nicotine exposure on birth outcomes through their influence on nicotine metabolism. Greatly increased risk of cigarette smoke-induced diseases, including low birthweight, has been found in individuals with susceptible genotypes. Interventions to control maternal smoking are also considered.

Maternal Prenatal Nutrition and Health in Grandchildren and Subsequent Generations

This review focuses on how maternal prenatal nutritional states may affect the health of grandchildren and later generations. We first summarize the limited current data in human populations relating to the potential transmission of phenotypes across multiple generations that result from the nutritional experience of a pregnant woman. We then discuss findings from other species, especially mammals, that provide important clues as to whether, and if so how, such transmission could occur in humans. Finally, we consider how studies of human populations could be best designed to detect transmission across multiple generations. We argue that just as epidemiologists embraced a life-course perspective to human health and disease in the twentieth century, we must now seek to better understand how health and disease could be shaped across multiple generations.

Intergenerational correlations in size at birth and the contribution of environmental factors: The Uppsala Birth Cohort Multigenerational Study, Sweden, 1915-2002

Sizes at birth of parents and their children are known to be correlated, reflecting in part the influence of fetal and maternal genes. Sociodemographic factors, regarded as aspects of the shared environment across generations, would also be expected to contribute, but evidence is limited. In the present study, the authors aimed to quantify the role of the shared environment in explaining intergenerational correlations in birth weight and length by using data across 3 consecutive generations from the Uppsala Birth Cohort Multigenerational Study in Uppsala, Sweden. That study included birth and sociodemographic data on 7,657 singletons born in Uppsala in 1915-1929 (generation 1) and their grandchildren (generation 3). Standard regression and biometric models were used to study the correlations in size at birth of generation 1-generation 3 pairs. The data showed stronger correlations in maternal pairs than in paternal pairs for birth weight (0.125 vs. 0.096, P = 0.02) but not for birth length (0.097 vs. 0.093, P = 0.77). These correlations were not reduced by adjustment for sociodemographic factors in regression models. In contrast, significant shared-environment contributions to the intergenerational correlations were identified in biometric models, averaging 14% for both birth measures. These models assumed a common latent factor for the sociodemographic variables. The present results show that the shared environment moderately but significantly contributes to intergenerational correlations.

Intergenerational birth weight associations by mother's birth order - the mechanisms behind the paradox: a population-based cohort study

BACKGROUND

Mother's birth order is inversely associated with offspring birth weight despite positively associated with the mother's own birth weight. The causes behind this relation have not been elucidated.

AIMS

To investigate the relation between mother's birth order and birth weight of her offspring, with emphasis on possible mechanisms behind the findings.

STUDY DESIGN

Population based cohort study over two generations.

SUBJECTS

Data were from the Medical Birth Registry of Norway, based on all births in Norway, 1967-2006 (2.3 million births). Units where both mothers and offspring were singletons and offspring were first born were included, forming 272,674 mother-offspring units for the analyses.

OUTCOME MEASURE

Birth weight in the second generation.

RESULTS

Mother's birth weight increased steadily with increasing birth order from 3369 g for first born to 3538 g for fourth or later born mothers. In contrast, there was a monotonic decrease in offspring mean birth weight with increasing mother's birth order (9.1 g per birth order (95% C.I.; 6.8, 11.4)). First born mothers tended to be older, to have higher education, to more often be married or cohabiting, and to smoke less than later born mothers at the time of their first pregnancy.

CONCLUSION

The general reduction in mean birth weight among first born mothers was not observed in the next generation. We suggest that first born mothers have the same biologically potential for achieving similar sized offspring as later born mothers, and that social factors account for the inverse relation.

Maternal birthweight and outcome of twin pregnancy

There is evidence from singletons that maternal birthweight is positively related to offspring gestational length and birthweight, and some evidence of an inverse relationship with preterm birth. Among twins very preterm birth is the major cause of neonatal mortality and of immediate and later morbidity, including neurodevelopmental impairment. We hypothesised that the relationship between maternal birthweight and gestational length would be more evident in twin than in singleton pregnancies, as there is more variation in gestation in the former. Among 131 singleton mothers carrying twins, there was weak evidence of a positive relationship between maternal birthweight and twin gestational length (+0.6 weeks [95% CI -0.05, +1.3] per kg increase in maternal birthweight, but stronger evidence among 56 of these who went into labour spontaneously (+1.9 weeks [+0.7, +3.1], P = 0.003 for interaction). In the latter group we estimated that the odds of very preterm birth (at <32 weeks) were reduced by 50% [95% CI 10%, 82%] per 250 g increase in maternal birthweight. In the whole cohort, and in this subgroup, maternal birthweight was strongly positively related to both twin offspring total birthweight and total placental weight. Our data, consistent with intergenerational programming of early development, suggest the possibility of a stronger and more clinically relevant association among twins than among singletons. Nevertheless, our sample size was modest and this finding needs to be confirmed in a larger cohort.

Obstetrician-assessed maternal health at pregnancy predicts offspring future health

Background

We aimed to examine the association between obstetrician assessment of maternal physical health at the time of pregnancy and offspring cardiovascular disease risk.

Methods and Principal Findings

We examined this association in a birth cohort of 11,106 individuals, with 245,000 person years of follow-up. We were concerned that any associations might be explained by residual confounding, particularly by family socioeconomic position. In order to explore this we used multivariable regression models in which we adjusted for a range of indicators of socioeconomic position and we explored the specificity of the association. Specificity of association was explored by examining associations with other health related outcomes. Maternal physical health was associated with cardiovascular disease: adjusted (socioeconomic position, complications of pregnancy, birthweight and childhood growth at mean age 5) hazard ratio comparing those described as having poor or very poor health at the time of pregnancy to those with good or very good health was 1.55 (95%CI: 1.05, 2.28) for coronary heart disease, 1.91 (95%CI: 0.99, 3.67) for stroke and 1.57 (95%CI: 1.13, 2.18) for either coronary heart disease or stroke. However, this association was not specific. There were strong associations for other outcomes that are known to be related to socioeconomic position (3.61 (95%CI: 1.04, 12.55) for lung cancer and 1.28 (95%CI:1.03, 1.58) for unintentional injury), but not for breast cancer (1.10 (95%CI:0.48, 2.53)).

Conclusions and Significance

These findings demonstrate that a simple assessment of physical health (based on the appearance of eyes, skin, hair and teeth) of mothers at the time of pregnancy is a strong indicator of the future health risk of their offspring for common conditions that are associated with poor socioeconomic position and unhealthy behaviours. They do not support a specific biological link between maternal health across her life course and future risk of cardiovascular disease in her offspring.

Fetal origins of developmental plasticity: are fetal cues reliable predictors of future nutritional environments?

Evidence that fetal nutrition triggers permanent adjustments in a wide range of systems and health outcomes is stimulating interest in the evolutionary significance of these responses. This review evaluates the postnatal adaptive significance of fetal developmental plasticity from the perspective of life history theory and evolutionary models of energy partitioning. Birthweight is positively related to multiple metabolically costly postnatal functions, suggesting that the fetus has the capacity to distribute the burden of energy insufficiency when faced with a nutritionally challenging environment. Lowering total requirements may reduce the risk of negative energy balance, which disproportionately impacts functions that are not essential for survival but that are crucial for reproductive success. The long-term benefit of these metabolic adjustments is contingent upon the fetus having access to a cue that is predictive of its future nutritional environment, a problem complicated in a long-lived species by short-term ecologic fluctuations like seasonality. Evidence is reviewed suggesting that the flow of nutrients reaching the fetus provides an integrated signal of nutrition as experienced by recent matrilineal ancestors, which effectively limits the responsiveness to short-term ecologic fluctuations during any given pregnancy. This capacity for fetal nutrition to minimize the growth response to transient ecologic fluctuations is defined here as intergenerational "phenotypic inertia," and is hypothesized to allow the fetus to cut through the "noise" of seasonal or other stochastic influences to read the "signal" of longer-term ecologic trends. As a mode of adaptation, phenotypic inertia may help the organism cope with ecologic trends too gradual to be tracked by conventional developmental plasticity, but too rapid to be tracked by natural selection. From an applied perspective, if a trait like fetal growth is designed to minimize the effects of short-term fluctuations by integrating information across generations, public health interventions may be most effective if focused not on the individual but on the matriline.

Type 2 diabetes in grandparents and birth weight in offspring and grandchildren in the ALSPAC study

OBJECTIVE

To examine the association between a history of type 2 diabetes and birth weight of offspring and grandchildren.

DESIGN

Prospective observational study. Diabetic status, as reported by mothers (F1 generation) was collected on grandparents (F0) of babies (F2) born to mothers (F1) who participated in a study of maternal and child health. Associations between risk of grandparental diabetes and birth weight in mothers (F1) and grandchildren (F2) were analysed using linear and logistic regression.

SETTING

Avon: comprising of the city of Bristol and surrounding areas.

PARTICIPANTS

12 076 singleton babies (F2), their parents (F1) and maternal and paternal grandparents (F0).

RESULTS

Women (F1) who had no parents with type 2 diabetes had lower birth weights than women with one or two diabetic parents, after controlling for the age of both parents. There was a U shaped association between maternal birth weight and grandmaternal diabetes, but no evidence of an association with grandpaternal diabetes. The grandchildren of maternal grandparents with type 2 diabetes were more likely to be in the top tertile of birth weight than grandchildren of non-diabetics. There was evidence for an inverted U shaped association between birth weight of grandchildren and diabetes in paternal grandmothers.

CONCLUSIONS

This is the first study to show intergenerational associations between type 2 diabetes in one generation and birth weight in the subsequent two generations. While the study has limitations mainly because of missing data, the findings nevertheless provide some support for the role of developmental intrauterine effects and genetically determined insulin resistance in impaired insulin mediated growth in the fetus.

Integrated perinatal health framework. A multiple determinants model with a life span approach

BACKGROUND

Despite great strides in improving prenatal care utilization among American women, key perinatal indicators have remained stagnant or worsened in the past decade, and the United States continues to rank near the bottom compared to other developed countries. A new approach is needed if we are to achieve improvements in perinatal health.

METHODS

To propose a new framework that integrates a "life span" approach with a multiple determinants model.

RESULTS

We recognize that (1) powerful influences on outcome occur long before pregnancy begins; (2) pregnancy outcome is shaped by social, psychological, behavioral, environmental, and biological forces; and (3) the demography of pregnancy has changed dramatically in the last few decades with more women delaying their first birth. Approaches that simultaneously consider the entire life span as well as multiple determinants may need to be adopted. We propose a framework that integrates these approaches and is supported by the research literature. The life span perspective focuses attention toward the preconceptional and interconceptional periods as targets for intervention in improving perinatal health. The multiple determinants model distinguishes among concepts of disease, health and functioning, and well-being for both women and their offspring.

CONCLUSIONS

Our intent is to influence how policymakers, public health professionals, clinicians, and researchers approach perinatal health.

Racial and ethnic disparities in birth outcomes: a life-course perspective

BACKGROUND

In the United States, Black infants have significantly worse birth outcomes than do White infants. The cause of these persisting racial disparities remains unexplained. Most extant studies focus on differential exposures to protective and risk factors during pregnancy, such as current socioeconomic status, maternal risky behaviors, prenatal care, psychosocial stress, or perinatal infections. These risk factors during pregnancy, however, do not adequately account for the disparities.

METHODS

We conducted a literature review for longitudinal models of health disparities, and presented a synthesis of two leading models, using a life-course perspective. Traditional risk factors during pregnancy are then reexamined within their life-course context. We conclude with a discussion of the limitations and implications of the life-course perspective for future research, practice, and policy development.

RESULTS

Two leading longitudinal models of health disparities were identified and discussed. The early programming model posits that exposures in early life could influence future reproductive potential. The cumulative pathways model conceptualizes decline in reproductive health resulting from cumulative wear and tear to the body's allostatic systems. We propose a synthesis of these two models, using the life-course perspective. Disparities in birth outcomes are the consequences of differential developmental trajectories set forth by early life experiences and cumulative allostatic load over the life course.

CONCLUSIONS

Future research on racial disparities in birth outcomes needs to examine differential exposures to risk and protective factors not only during pregnancy, but over the life course of women. Eliminating disparities requires interventions and policy development that are more longitudinally and contextually integrated than currently prevail.

Paternal contribution to birth weight

STUDY OBJECTIVE

Understanding causes of variation in birth weight has been limited by lack of sufficient sets of data that include paternal birth weight. The objective was to estimate risks of low birth weight dependent on parental birth weights and to estimate father-mother-offspring correlations for birth weight to explain the variability in birth weight in terms of effects of genes and environmental factors.

DESIGN

A family design, using trios of father-mother-firstborn child.

SETTING

The complete birth population in Norway 1967-98.

PARTICIPANTS

67 795 families.

MAIN RESULTS

The birth weight correlations were 0.226 for mother-child and 0.126 for father-child. The spousal correlation was low, 0.020. The relative risk of low birth weight in the first born child was 8.2 if both parents were low birth weight themselves, with both parents being above 4 kg as the reference. The estimate of heritability is about 0.25 for birth weight, under the assumption that cultural transmission on the paternal side has no effect on offspring prenatal growth.

CONCLUSIONS

Paternal birth weight is a significant and independent predictor of low birth weight in offspring. The estimate of the heritability of birth weight in this study is lower than previously estimated from data within one generation in the Norwegian population.

The Washington State Intergenerational Study of Birth Outcomes: methodology and some comparisons of maternal birthweight and infant birthweight and gestation in four ethnic groups

A statewide database of vital records and hospital discharge summaries of obstetric and neonatal admissions for Washington State in 1987-95 was linked to the birth certificates of mothers born in the state. A total of 46,000 births to mothers of four racial/ethnic groups were studied: Whites, African-Americans, Native Americans and Hispanics. For all four groups inverse associations were found between maternal birthweight and infant low birthweight and preterm birth. The birthweight distribution of African-American mothers was displaced markedly downwards compared with the Whites; this difference in maternal birthweight is offered as a partial explanation of the greater prevalence of suboptimal pregnancy outcomes in the former. In contrast, the maternal birthweight distributions of Whites, Native Americans and Hispanics are similar; differences in pregnancy outcomes are probably more related to maternal preconceptional and postnatal factors in these groups as well as differences in pregnancy-related factors. Mothers' birthweight may have clinical value in identifying high-risk pregnancies.

The intergenerational relationship between mother's birthweight, infant birthweight and infant mortality in black and white mothers

The relationship between the birthweight of white and black mothers and the outcomes of their infants were examined using the 1988 National Maternal and Infant Health Survey. White and black women who were low birthweight themselves were at increased risk of delivering very low birthweight (VLBW), moderately low birthweight (MLBW), extremely preterm and small size for gestational age (SGA) infants. Adjustment for the confounding effects of prepregnant weight and height reduced the risks of all these outcomes slightly, and more substantially reduced the maternal birthweight associated risk of moderately low birthweight among white mothers. There was little effect of maternal birthweight on infant birthweight-specific infant mortality in white mothers; however, black mothers who weighed less than 4 lbs at birth were at significantly increased risk of delivering a normal birthweight infant who subsequently died. Although the risks for the various outcomes associated with low maternal birthweight were not consistently higher in black mothers compared with white mothers, adjustment for prepregnant weight and height had a greater effect in white mothers than in black mothers. We suggest that interventions to reduce the risks for adverse pregnancy outcomes associated with low maternal birthweight should attempt to optimise prepregnant weight and foster child health and growth.