Parental determinants of birth weight

Associations of telomere length at birth with predicted atherosclerotic lesions and cardiovascular disease risk factors in midlife: A 40-year longitudinal study

BACKGROUND AND AIMS

Adult telomere length (TL) is substantially determined by birth TL, but associations of birth TL with cardiovascular disease (CVD) are unknown.

METHODS

We included 144 adult offspring born in 1959-1966 from the Collaborative Perinatal Project, a US birth cohort. Birth TL was measured from banked cord blood with quantitative polymerase chain reaction. Atherosclerotic lesions were predicted by the Pathobiological Determinants of Atherosclerosis in Youth (PDAY) score that was based on blood pressure, lipids, hemoglobin A1c, and body weight at the midlife follow-up in 2003-2008 (average age: 42 years). Information on midlife CVD risk factors including the age at first diagnoses of hypertension, hypercholesterolemia, and diabetes was also collected. We used linear and logistic regression models to analyze associations of birth TL with the continuous PDAY score and categorical CVD risk factors, respectively, adjusting for prenatal confounders.

RESULTS

At midlife follow-up, 31.2% and 18.7% of participants had ever been diagnosed with hypercholesterolemia and hypertension, respectively, and 8.3% met the criteria for metabolic syndrome. Short birth TL (Quartile 1, Q1) was associated with a higher PDAY score (adjusted β: 1.78, 95% CI: 0.31, 3.25), increased odds of hypercholesterolemia (adjusted odds ratio [OR]: 3.23, 95% CI: 1.28, 8.18) and the presence of any cardiometabolic abnormalities (adjusted OR: 2.54, 95% CI: 1.00, 6.48) as compared to longer birth TL (Q2-Q4) after adjusting for prenatal confounders.

CONCLUSIONS

People born with short TL may be at increased risk of predicted midlife atherosclerotic lesions and hypercholesterolemia. Future studies with larger sample sizes and CVD morbidities are warranted to replicate our findings.

The effect of paternal factors on perinatal and paediatric outcomes: a systematic review and meta-analysis

BACKGROUND

Maternal factors, including increasing childbearing age and various life-style factors, are associated with poorer short- and long-term outcomes for children, whereas knowledge of paternal parameters is limited. Recently, increasing paternal age has been associated with adverse obstetric outcomes, birth defects, autism spectrum disorders and schizophrenia in children.

OBJECTIVE AND RATIONALE

The aim of this systematic review is to describe the influence of paternal factors on adverse short- and long-term child outcomes.

SEARCH METHODS

PubMed, Embase and Cochrane databases up to January 2017 were searched. Paternal factors examined included paternal age and life-style factors such as body mass index (BMI), adiposity and cigarette smoking. The outcome variables assessed were short-term outcomes such as preterm birth, low birth weight, small for gestational age (SGA), stillbirth, birth defects and chromosomal anomalies. Long-term outcome variables included mortality, cancers, psychiatric diseases/disorders and metabolic diseases. The systematic review follows PRISMA guidelines. Relevant meta-analyses were performed.

OUTCOMES

The search included 14 371 articles out of which 238 met the inclusion criteria, and 81 were included in quantitative synthesis (meta-analyses). Paternal age and paternal life-style factors have an association with adverse outcome in offspring. This is particularly evident for psychiatric disorders such as autism, autism spectrum disorders and schizophrenia, but an association is also found with stillbirth, any birth defects, orofacial clefts and trisomy 21. Paternal height, but not BMI, is associated with birth weight in offspring while paternal BMI is associated with BMI, weight and/or body fat in childhood. Paternal smoking is found to be associated with an increase in SGA, birth defects such as congenital heart defects, and orofacial clefts, cancers, brain tumours and acute lymphoblastic leukaemia. These associations are significant although moderate in size, with most pooled estimates between 1.05 and 1.5, and none exceeding 2.0.

WIDER IMPLICATIONS

Although the increased risks of adverse outcome in offspring associated with paternal factors and identified in this report represent serious health effects, the magnitude of these effects seems modest.

Fetal growth is associated with CpG methylation in the P2 promoter of the IGF1 gene

Background

There are many reasons to think that epigenetics is a key determinant of fetal growth variability across the normal population. Since IGF1 and INS genes are major determinants of intrauterine growth, we examined the methylation of selected CpGs located in the regulatory region of these two genes.

Methods

Cord blood was sampled in 159 newborns born to mothers prospectively followed during their pregnancy. A 142-item questionnaire was filled by mothers at inclusion, during the last trimester of the pregnancy and at the delivery. The methylation of selected CpGs located in the promoters of the IGF1 and INS genes was measured in cord blood mononuclear cells collected at birth using bisulfite-PCR-pyrosequencing.

Results

Methylation at IGF1 CpG-137 correlated negatively with birth length (r = 0.27, P = 3.5 × 10⁻⁴). The same effect size was found after adjustment for maternal age, parity, and smoking: a 10% increase in CpG-137 methylation was associated with a decrease of length by 0.23 SDS.

Conclusion

The current results suggest that the methylation of IGF1 CpG-137 contributes to the individual variation of fetal growth by regulating IGF1 expression in fetal tissues.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0489-9) contains supplementary material, which is available to authorized users.

Assessing the Causal Relationship of Maternal Height on Birth Size and Gestational Age at Birth: A Mendelian Randomization Analysis

BACKGROUND

Observational epidemiological studies indicate that maternal height is associated with gestational age at birth and fetal growth measures (i.e., shorter mothers deliver infants at earlier gestational ages with lower birth weight and birth length). Different mechanisms have been postulated to explain these associations. This study aimed to investigate the casual relationships behind the strong association of maternal height with fetal growth measures (i.e., birth length and birth weight) and gestational age by a Mendelian randomization approach.

METHODS AND FINDINGS

We conducted a Mendelian randomization analysis using phenotype and genome-wide single nucleotide polymorphism (SNP) data of 3,485 mother/infant pairs from birth cohorts collected from three Nordic countries (Finland, Denmark, and Norway). We constructed a genetic score based on 697 SNPs known to be associated with adult height to index maternal height. To avoid confounding due to genetic sharing between mother and infant, we inferred parental transmission of the height-associated SNPs and utilized the haplotype genetic score derived from nontransmitted alleles as a valid genetic instrument for maternal height. In observational analysis, maternal height was significantly associated with birth length (p = 6.31 × 10-9), birth weight (p = 2.19 × 10-15), and gestational age (p = 1.51 × 10-7). Our parental-specific haplotype score association analysis revealed that birth length and birth weight were significantly associated with the maternal transmitted haplotype score as well as the paternal transmitted haplotype score. Their association with the maternal nontransmitted haplotype score was far less significant, indicating a major fetal genetic influence on these fetal growth measures. In contrast, gestational age was significantly associated with the nontransmitted haplotype score (p = 0.0424) and demonstrated a significant (p = 0.0234) causal effect of every 1 cm increase in maternal height resulting in ~0.4 more gestational d. Limitations of this study include potential influences in causal inference by biological pleiotropy, assortative mating, and the nonrandom sampling of study subjects.

CONCLUSIONS

Our results demonstrate that the observed association between maternal height and fetal growth measures (i.e., birth length and birth weight) is mainly defined by fetal genetics. In contrast, the association between maternal height and gestational age is more likely to be causal. In addition, our approach that utilizes the genetic score derived from the nontransmitted maternal haplotype as a genetic instrument is a novel extension to the Mendelian randomization methodology in casual inference between parental phenotype (or exposure) and outcomes in offspring.

An integrative model of inter- and intragenerational preconception processes influencing birthweight in the United States

Social inequalities in birthweight are an important population health concern as low birthweight is one mechanism through which inequalities are reproduced across generations. Yet, we do not understand what causes these social inequalities. This study draws together theoretic and empiric findings from disparate disciplines--sociology, economics, public health, and behavior genetics--to develop a new integrative intra- and intergenerational model of preconception processes influencing birthweight. This model is empirically tested using structural equation modeling and population-level data containing linked mother-daughter pairs from the National Longitudinal Survey of Youth (NLSY79) and the Children of the NLSY79 (N = 1,580 mother-daughter pairs). Results reveal that birthweight is shaped by preconception factors dating back to women's early life environment as well as conditions dating back three generations, via integrative intra- and intergenerational processes. These processes reveal specific pathways through which social inequality can transmit from mothers to children via birthweight.

Genetic influences on the association between fetal growth and susceptibility to type 2 diabetes

The fetal insulin hypothesis proposes that low birth weight and susceptibility to type 2 diabetes (T2D) could both be two phenotypes of the same genotype. Insulin is a key growth factor in utero, and T2D is characterized by insulin resistance and/or beta-cell dysfunction. Therefore, genetic variants impacting on insulin secretion and action are likely to alter both fetal growth and susceptibility to T2D. There are three lines of evidence in support of this hypothesis. (1) Studies of rare monogenic diabetes have shown mutations in a single gene, such as GCK or KCNJ11, can cause diabetes by reducing insulin secretion, and these mutations are also associated with reduced birth weight. (2) Epidemiological studies have indicated that children born to fathers with diabetes are born smaller. As the father cannot influence the intrauterine environment, this association is likely to reflect genes inherited by the fetus from the father. (3) The most compelling evidence comes from recent genome-wide association studies. Variants in the CDKAL1 and HHEX-IDE genes that predispose to diabetes, if present in the fetus, are associated with reduced birth weight. These data provide evidence for a genetic contribution to the association between low birth weight and susceptibility to T2D. This genetic background is important to take into consideration when investigating the impact of environmental determinants and developing strategies for intervention and prevention.

Birth weight, infant mortality, and race: twin comparisons and genetic/environmental inputs

Genetic and environmental inputs may shape population health disparities in varying ways. In this article, we use unique variation involved in twin births to attempt to untangle how genetic and prenatal environmental variation may make different contributions to infant health among white and black populations in the United States. Using twin fixed effects models and data from the 1995-1997 Matched Multiple Birth Dataset we compare birth weight-mortality associations across twin sex composition, zygosity, and race. Findings reveal suggestive differences between fraternal and imputed identical twin estimates for white and black twin pairs.

Biracial couples and adverse birth outcomes: a systematic review and meta-analyses

BACKGROUND

Differences in birth outcomes such as low birthweight (LBW), preterm births (PTB), stillbirth, differences in birthweight in Black vs. White race are well known. Infants born to biracial parents (mother and father from either Black or White races) also experience higher adverse birth outcomes.

OBJECTIVE

To systematically review and meta-analyze birth outcomes among parents of mixed racial background compared to parents of same race.

SEARCH STRATEGY

Medline, Embase, CINAHL and bibliographies of identified articles were searched for English language studies.

SELECTION CRITERIA

Studies reporting association between parental mixed racial status and LBW, PTB, or small-for-gestational age (SGA) outcomes were included. DATA COLLECTION AND ANALYSES: After exclusion of duplicate cohorts in different publications, data from White mother-Black father (WMBF), Black mother-White father (BMWF) and Black mother-Black father (BMBF) groups were compared with the White mother-White father (WMWF) group.

RESULTS

Eight English language studies from of 26 335 596 singleton births were included and reviewed. Compared to the WMWF group, the adjusted odds ratio (95% confidence intervals) were: (a) low birthweight; 1.21 (1.10-1.33) for WMBF, 1.75(1.64-1.87) for BMWF, and 2.08 (1.81-2.38) for BMBF; (b) preterm births; 1.17 (1.05-1.31) for WMBF, 1.37 (1.18-1.59) for BMWF, and 1.78 (1.59-2.00) for BMBF; and (c) stillbirths; 1.43 (0.92-2.21) for WMBF, 1.51 (1.09-2.08) for BMWF, and 1.85 (1.47-2.32) for BMBF.

CONCLUSION

Biracial status of parents was associated with higher risk for adverse pregnancy outcomes than both White parents but lower than both Black parents, with maternal race having a greater influence than paternal race on pregnancy outcomes.

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.

Paternal factors and low birthweight, preterm, and small for gestational age births: a systematic review

A systematic review of the risks of a low birthweight (LBW), preterm, and small-for-gestational-age births in relation to paternal factors was performed. Medline, Embase, Cumulative Index of Nursing and Allied Health Literature, and bibliographies of identified articles were searched for English-language studies. Study qualities were assessed according to a predefined checklist. Thirty-six studies of low-to-moderate risk of bias were reviewed for various paternal factors: age, height, weight, birthweight, occupation, education, and alcohol use. Extreme paternal age was associated with higher risk for LBW. Among infants who were born to tall fathers, birthweight was approximately 125-150 g higher compared with infants who were born to short fathers. Paternal LBW was associated with lower birthweight of the offspring. In conclusion, paternal characteristics including age, height, and birthweight are associated with LBW. Paternal occupational exposure and low levels of education may be associated with LBW; however, further studies are needed.

Heritability of childhood weight gain from birth and risk markers for adult metabolic disease in prepubertal twins

OBJECTIVE

Associations between size at birth, postnatal weight gain, and potential risk for adult disease have been variably explained by in utero exposures or genetic risk that could affect both outcomes. We utilized a twin model to explore these hypotheses.

METHODS

One hundred pairs of healthy twins aged 8.9 yr (range, 7.2-10.9 yr) had fasting blood samples collected, blood pressure (BP) measured, and anthropometry assessed. All measurements were converted to sd scores (SDS) to adjust for age and sex.

RESULTS

Mean birth weights in both monozygotic and dizygotic twins were -0.90 SDS lower than the UK reference. In postnatal life, 58% of monozygotic twins and 59% of dizygotic twins showed rapid weight gain (a change of more than +0.67 in weight SDS) from birth. Postnatal weight gain was positively associated with sum of skinfolds (r = 0.51; P < 0.0005), fasting insulin levels (r = 0.35; P < 0.0005), systolic BP (r = 0.30; P < 0.0005), and diastolic BP (r = 0.15; P < 0.05) at follow-up. Heritability estimates (additive genetic components) were calculated using variance components models for: birth weight, 44%; postnatal weight gain, 80%; childhood height, 89%; body mass index, 72%; sum of skinfolds, 89%; waist circumference, 74%; fasting insulin, 65%; systolic BP, 33%; and diastolic BP, 29%.

CONCLUSIONS

Postnatal weight gain from birth, rather than birth weight, was associated with childhood risk markers for adult metabolic disease. Childhood weight gain was highly heritable, and genetic factors associated with postnatal weight gain are likely to also contribute to risks for adult disease.

Childhood obesity: are genetic differences involved?

This brief review focuses on the genetic contribution to childhood obesity. Evidence for a genetic component to excess body weight during growth is presented from the perspective of genetic epidemiology studies. Parental obesity is a predictor of childhood excess weight. The familial risk ratio for childhood obesity when a parent is obese reaches >2.5. Birth weight is characterized by a genetic heritability component on the order of 30%, with significant maternal and paternal effects in addition to the newborn genes. About 5% of childhood obesity cases are caused by a defect that impairs function in a gene, and >/=5 of these genes have been uncovered. However, the common forms of childhood obesity seem to result from a predisposition that primarily favors obesogenic behaviors in an obesogenic environment. Candidate gene and genomewide association studies reveal that these obesogenic genes have small effect sizes but that the risk alleles for obesity are quite common in populations. The latter may translate into a highly significant population-attributable risk of obesity. Gene-environment interaction studies suggest that the effects of predisposing genes can be enhanced or diminished by exposure to relevant behaviors. It is possible that the prevalence of childhood obesity is increasing across generations as a result of positive assortative mating with obese husbands and wives contributing more obese offspring than normal-weight parents.

Regulation of fetal growth: consequences and impact of being born small

The first trimester of pregnancy is the time during which organogenesis takes place and tissue patterns and organ systems are established. In the second trimester the fetus undergoes major cellular adaptation and an increase in body size, and in the third trimester organ systems mature ready for extrauterine life. In addition, during that very last period of intrauterine life there is a significant increase in body weight. In contrast to the postnatal endocrine control of growth, where the principal hormones directly influencing growth are growth hormone (GH) and the insulin-like growth factors (IGFs) via the GH-IGF axis, fetal growth throughout gestation is constrained by maternal factors and placental function and is coordinated by growth factors. In general, growth disorders only become apparent postnatally, but they may well be related to fetal life. Thus, fetal growth always needs to be considered in the overall picture of human growth as well as in its metabolic development.

Modeling genetic and environmental factors to increase heritability and ease the identification of candidate genes for birth weight: a twin study

Heritability estimates of birth weight have been inconsistent. Possible explanations are heritability changes during gestational age or the influence of covariates (e.g. chorionicity). The aim of this study was to model birth weights of twins across gestational age and to quantify the genetic and environmental components. We intended to reduce the common environmental variance to increase heritability and thereby the chance of identifying candidate genes influencing the genetic variance of birth weight. Perinatal data were obtained from 4232 live-born twin pairs from the East Flanders Prospective Twin Survey, Belgium. Heritability of birth weights across gestational ages was estimated using a non-linear multivariate Gaussian regression with covariates in the means model and in covariance structure. Maternal, twin-specific, and placental factors were considered as covariates. Heritability of birth weight decreased during gestation from 25 to 42 weeks. However, adjusting for covariates increased the heritability over this time period, with the highest heritability for first-born twins of multipara with separate placentas, who were staying alive (from 52% at 25 weeks to 30% at 42 weeks). Twin-specific factors revealed latent genetic components, whereas placental factors explained common and unique environmental factors. The number of placentas and site of the insertion of the umbilical cord masked the effect of chorionicity. Modeling genetic and environmental factors leads to a better estimate of their role in growth during gestation. For birth weight, mainly environmental factors were explained, resulting in an increase of the heritability and thereby the chance of finding genes influencing birth weight in linkage and association studies.

Three common intronic variants in the maternal and fetal thiamine pyrophosphokinase gene (TPK1) are associated with birth weight

Extreme variations in birth weight increase immediate postnatal mortality and morbidity, and are also associated with the predisposition to metabolic diseases in late adulthood. Birth weight in humans is influenced by yet unknown genetic factors. Since the 7q34-q35 region showed linkage with birth weight in a recent human genome scan (p = 8.10(-5)), this study investigated the TPK1 (thiamine pyrophosphokinase) gene locus, located in 7q34-36. Having found no coding variants in the TPK1 gene, we genotyped 43 non coding SNPs spanning a region of 420kb, and used the QTDT method to test their association with birth weight in 964 individuals from 220 families of European ancestry. Family-based tests detected association of 8 SNPs with birth weight (p<0.008), but after correction for multiple tests only rs228581 C/T (p = 0.03), rs228582 A/G (p = 0.04) and rs228584 C/T (p = 0.03) were still associated with birth weight, as well as their T-A-T haplotype (p = 0.03). In addition, we found an association between maternal rs228584 genotype and offspring birth weight (p = 0.027). These observations suggest that genomic variations in the fetal and maternal TPK1 gene could contribute to the variability of birth weight in normal humans.

Identification of distinct quantitative trait Loci affecting length or weight variability at birth in humans

CONTEXT

The variability of human fetal growth is multifactorial. Twin and family studies demonstrate that genetic determinants influence normal fetal growth, but the responsible genetic polymorphisms are unknown.

OBJECTIVE

The objective of the study was the mapping of quantitative trait loci (QTLs) for birth length and weight.

DESIGN AND METHODS

To approach the genetic factors implicated in the normal variation of birth length and weight, we conducted a genome-wide approach of these two quantitative traits in 220 French Caucasian pedigrees (412 sibling pairs) using a variance components method.

RESULTS

We observed evidence for several QTLs influencing birth length or birth weight independently. Whereas birth length and weight showed a close correlation (r = 0.76, P < 0.0001), their genetic variability appeared largely determined by distinct genomic loci. Birth length was influenced by two major QTLs located in 2p21 and 2q11 (LOD scores 2.69 and 3.57). The variability of birth weight was linked to another QTL on 7q35 (LOD score 3.1). Several other regions showed more modest evidence for linkage with LOD score values of 1-2 on chromosomes 7, 8, 10, 13, and 17 for birth length and chromosomes 1, 2, 6, 8, 10, 13, 14, 15, 17, and 20 for birth weight.

CONCLUSION

These preliminary QTLs provide a first step toward the identification of the genomic variants involved in the variability of human fetal growth. Our results should, however, be considered preliminary until they are replicated in other studies.

The genetic contribution towards preterm delivery

Indirect evidence supports a possible genetic predisposition towards preterm birth. The recurrence of spontaneous preterm delivery in individual women, families and ethnic groups suggests a long-acting aetiology, consistent with a genetic factor. Genetic contributions from both mother and fetus probably play a role in determining gestational length. Preliminary genetic association studies implicate gene variants of tumor necrosis factor-alpha (TNF-alpha) in preterm birth. Further understanding of a genetic predisposition begins with investigation of the pathogenesis of preterm delivery. Technological advances in the study of the human genome (genomics) and protein complement (proteomics) will allow identification of novel genes and proteins involved in preterm delivery. Insight into the complex gene regulation and protein production in preterm delivery may contribute to an understanding of a genetic basis. A discovered genetic factor may lead to medical breakthroughs and reductions in prematurity, neonatal morbidity and mortality.

Parental race, birth weight, gestational age, and fetal growth among twin infants in the United States

BACKGROUND

No previous study has examined the association between paternal race and birth weight among twins.

AIMS

To examine the association of parents' race and birth weight among twins.

STUDY DESIGN

Population-based retrospective cohort study to examine the association between parents' race and birth weight, and its two components, gestation duration and fetal growth among four group of infants: both parents blacks (FB-MB), father white and mother black (FW-MB), father black and mother white (FB-MW), and both parents whites (FW-MW), with "risk-free" analysis to control confounding factors.

SUBJECTS

Twin births (304,466 twins) registered in the United States in 1995-1997.

OUTCOME MEASURES

The means of birth weight, gestational age, and birth-weight-for-gestational age z score, and rates of very low birth weight (VLBW, <1500 g), very preterm birth (VPTB, <32 weeks of gestation), and fetal growth restriction (FGR, <10th percentile of z score).

RESULTS

Means of birth weight, gestational age, and z score were 2234.0, 2301.9, 2361.1, and 2433.8, and 35.02, 35.24, 35.65, and 35.78, and -0.136, -0.070, -0.039, and 0.063, respectively, and the rates of VLBW, VPTB, and FGR were 14.5, 12.3, 10.5, and 8.1, and 16.0, 13.0, 11.6, and 9.2, and 12.6, 11.1, 10.8, and 8.7, respectively, in the FB-MB, FW-MB, FB-MW, and FW-MW groups. Excluding subjects with various risk factors by risk-free analysis did not change the results.

CONCLUSIONS

Both parents' races are important determinants of birth weight, gestational age, and fetal growth among twin pregnancies, with higher effect on gestational age and greater maternal influence than paternal influence.

Intergenerational effects on size at birth in South India

Several studies have shown that a baby's birthweight correlates with the birthweight and adult size of both its parents, but more strongly with those of its mother, suggesting that both the 'maternal environment' and inherited genes influence size at birth. There are no previous such intergenerational data from India. Holdsworth Memorial Hospital (HMH), Mysore, South India, has preserved birth records containing the birthweight, length and head circumference of all newborns since 1934. We identified 468 mother-offspring and 341 father-offspring pairs born in the hospital. Daughters and sons (born 1990-95) were heavier at birth than their mothers and fathers, respectively, with a mean (SD) increase in birthweight of 121 g (24 g) between the two generations. The birthweight of both parents predicted offspring birthweight equally (mother: regression slope beta = 255 g/kg; father beta = 251 g/kg; P < 0.001 for both). Paternal birth length had a stronger effect than maternal birth length on offspring birth length. The mother's adult body mass index (BMI) had a greater effect than paternal BMI on offspring birthweight (mother: 18 g/kg/m(2); P < 0.001; father: 15 g/kg/m(2); P = 0.04). In a regression model including data for both parents (available for 57 children) this difference was greater (mother: 46 g/kg/m(2); P < 0.001; father: -10 g/kg/m(2); ns). In contrast, paternal height had stronger effects than maternal height on offspring birth length (mother: 0.8 mm/cm; ns; father: 1.5 mm/cm; P < 0.001). In conclusion, size at birth is influenced by a combination of environmental and genetic factors. Both maternal and paternal birthweight correlate with offspring size at birth. Maternal nutritional status (BMI) influences birthweight. Paternal factors appear to contribute to neonatal skeletal size.

Parents’ Growth in Childhood and the Birth Weight of Their Offspring

BACKGROUND

A person's birth weight is inversely related to both their own and their parents' cardiovascular disease mortality risk, but mechanisms underlying such transgenerational associations are unclear. We investigated the influence of the childhood growth of the mother or father on the birth weight of their first-born offspring.

METHODS

We used data from the long-term follow up (in 1997-1998) of 4999 children from 1352 families who participated in the Boyd Orr Survey of Diet and Health in Pre-War Britain (1937-1939). Complete information on childhood height, potential confounding variables, and the birth weight of first-born offspring was available for 637 subjects.

RESULTS

Mother's height in childhood was positively associated with her offspring's birth weight. Leg length, but not trunk length, was the component of maternal height associated with offspring birth weight. For each unit increase in z-score for maternal childhood leg length, there was a 96-g (95% confidence interval = 6-186) increase in offspring birth weight after controlling for childhood socioeconomic variables and adult height. There were weaker positive associations of paternal height and leg length in childhood with offspring birth weight. Associations were not confounded by maternal birth weight or midgrandparental height.

CONCLUSIONS

Our findings are consistent with the hypothesis that maternal growth during childhood influences offspring birth weight, independently of maternal birth weight, final attained height, or midgrandparental height. Because leg length is a sensitive marker of adverse nutritional and social exposures during childhood, these results suggest a key role for a mother's early environmental exposures as a determinant of her child's subsequent health.

Genetic and environmental influences on the tracking of body size from birth to early adulthood

OBJECTIVE

This study identified genetic and environmental influences on the tracking of body size from birth to 16 to 18.5 years of age.

RESEARCH METHODS AND PROCEDURES

Longitudinal information was collected from a nationally representative sample of Finnish twin adolescents (birth cohorts 1975 to 1979) and their parents through questionnaires mailed when the twins were ages 16 and 18.5 years old. The sample included 702 monozygotic, 724 same-sex dizygotic, and 762 opposite-sex dizygotic sets of twins. The measures used were length, weight, ponderal index (kilograms per cubic meters), and gestational age at birth, and height, weight, and body mass index (kilograms per square meters) at 16 to 18.5 years of age. The changes in genetic and environmental influences on body size from birth to early adulthood were analyzed by quantitative genetic modeling.

RESULTS

The twins who had a higher weight or ponderal index at birth were taller and heavier in early adulthood, whereas those who were longer at birth were taller, but not heavier, later in life. Adult height was affected more by the birth size than body mass index. In the genetic modeling analyses, the genetic factors accounting for the variation of body size became more apparent with age, and both genetic and environmental influences on stature had a sizable carry-over effect from birth to late adolescence, whereas for relative weight, the influences were more age-specific.

DISCUSSION

The genetic and environmental architecture of body size changes from birth to adulthood. Even in monozygotic twins who share their genetic background, the initially larger twin tended to remain larger, demonstrating the long-lasting effects of fetal environment on final body size.

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.

Evidence for an association between environmental tobacco smoke exposure and birthweight: a meta-analysis and new data

Because of the strong association of active smoking with fetal growth retardation, increasing interest has focused on whether there is also an association with exposure to environmental tobacco smoke (ETS). We examined this issue in a retrospective study and by conducting a review of the literature and data pooling. In our study, nonsmoking women with singleton livebirths born in 1986-87 (n = 992) provided information on exposure to ETS for 1 h or more per day and paternal smoking. The risk of low birthweight (LBW, < 2500 g) was not increased in infants of ETS-exposed women, but there was a somewhat increased risk for LBW at term (adjusted odds ratio [OR] 1.8, 95% confidence interval [CI] 0.6, 4.8) and small-for-gestational-age (< 10th percentile of weight; OR = 1.4, 95% CI = 0.8, 2.5). These results were in the range of 16 other studies in the literature that had odds ratios from 1.0 to 2.2. A weighted average of the results of all studies on LBW at term or small-for-gestational-age yielded a pooled estimate of 1.2 [95% CI = 1.1, 1.3] in nonsmoking women. The pooled estimate of mean birthweight indicated a decrement of 28 g with ETS exposure of nonsmoking women [95% CI = -41, -16], with a greater decrement (about 40 g) seen among more homogeneous studies.

Parents' estimation of psychomotor development in very low birthweight (VLBW) infants

BACKGROUND

Within a longitudinal developmental surveillance project we tested the accuracy of the Revised Prescreening Developmental Questionnaire (R-PDQ) to detect developmental retardation in very low birthweight (VLBW) infants.

METHODS

Seventy surviving VLBW-infants born between July 1992 and December 1993 were re-examined at 6 months corrected age. The parent-completed questionnaires (n = 67) were compared with developmental assessment using the Griffiths Developmental Scale.

RESULTS

At 6 months corrected age, normal results of the Griffiths Developmental Scale (developmental quotient > or = 81) were found in 61/67 (91%) VLBW-infants and in 45/67 (67%) questionnaires (no or one 'delay'). The parents identified all six infants with psychomotor retardation on the Griffiths Developmental Scale (co-positivity 100%). However, only 45/61 infants with normal development were so identified with the R-PDQ (co-negativity 74%, positive predictive value 27%).

CONCLUSIONS

The R-PDQ discovered all infants whose developmental quotient was two standard deviations below the mean on the Griffiths Developmental Scale. The relatively high proportion of false positive R-PDQ results corresponded to lower developmental quotients within the normal range. Therefore, the R-PDQ provides a useful screening instrument for VLBW-infants.

Correlations of birth weight and gestational age across generations

Maternal birth weight is known to be a predictor of offspring birth weight. Less is known about the recurrence of gestational age. In order to estimate the recurrence risk of low birth weight and preterm birth across generations in a population-based sample, 11,092 pairs of mother-firstborn offspring were obtained through an internal linkage in the Norwegian Birth Registry based on the years 1967-1969 (mothers) and 1986-1989 (offspring). A low correlation coefficient of 0.086 was found for gestational age across generations, whereas the correlation between maternal and offspring birth weight was 0.242. Mothers with birth weight below 2500 g had a significantly increased risk (odds ratio = 3.03, 95% conf. interval 1.79-5.11) of having a low birth weight child compared with mothers with birth weight above 4 kg. On the other hand, if the mother was born before the 37th completed week of gestation, the risk of having a preterm child was not significantly increased (odds ratio = 1.46, conf. interval 0.96-2.21) compared with mothers who were born at term. Thus, in contrast to birth weight, human variation in gestational age does not appear to be influenced by genetic factors to any large degree.

Spastic quadriplegia in Western Australia. II: Pedigrees and family patterns of birthweight and gestational age

Pedigrees were obtained for all 74 index children and for three controls for each case. Recurrence of similar spastic quadriplegic phenotypes occurred in two families. A karyotype of 46,XY,dup(13)(q14q34), resulting in a partial trisomy 13, was found in another case. Rates of miscarriages and stillbirths plus neonatal deaths were higher among siblings of index cases than in siblings of birth-year controls, but were similar to siblings of birthweight controls. Average birthweights and gestational ages were lower in index cases than in birth-year controls. Children with spastic quadriplegia had significantly lower birthweights and gestational ages than their siblings. However, they also tended to come from families with a pattern of low birthweight and preterm delivery. The differences between families remained after controlling for factors affecting birthweight.

Chromosomal and genetic forms of growth failure

This chapter does not deal with single diseases, but gives a general account of chromosomal and genetically caused disturbances of growth; even a complete list and description of the various disorders would, in view of the large number of syndromes involving short stature, exceed its scope. Many chromosomal aberrations are non-viable disturbances of growth that lead to intrauterine amniotic death. Following a brief account of the normal development of the germ cell (gametogenesis, embryogenesis, phenogenesis) to the newborn, the incidence of the various chromosomal disturbances in the different stages of development and the effects on growth are discussed. In the case of chromosomal aberrations, particular attention is paid to the significance of mosaic formation. In addition, the new phenomena of genomic imprinting and uniparental disomy, exemplified by the Prader-Willi syndrome, are dealt with. Uniparental disomy, which was first demonstrated with the aid of molecular genetics, may provide an explanation for the sporadic appearance of many syndromes involving short stature. Many genes and environmental influences are involved in the individual shaping of body size so that a systematic classification of the various syndromes involving short stature is not possible. Finally, attention is drawn to the increased rate of formation of malignant tumours in certain syndromes involving disturbances of growth.

Maternal somatostatin levels and their correlation with infant birth weight

Samples of blood were obtained from 52 primiparous breast-feeding women 4 days post partum. Thirty-six of the mothers were still breast-feeding 3-4 months later and had further blood samples taken. Somatostatin levels were analyzed by radioimmunoassay. A highly significant rank correlation (P = 0.0001) between average somatostatin levels on the two occasions was established, although somatostatin levels recorded 3-4 months post partum were significantly higher than those found 4 days post partum (P less than 0.01). Furthermore, somatostatin levels obtained 4 days and 3-4 months post partum were inversely related to the birth weight of their children (P = 0.006 and P = 0.03). The significant negative correlation between somatostatin levels recorded 4 days post partum and birth weight of the infants persisted only when non-smokers were investigated. A strong positive correlation between infant birth weight and weight of placenta was found (P = 0.0001) and a negative correlation (P = 0.04) between somatostatin levels and placental weight. A stepwise regression was performed to explain the importance of somatostatin levels in birth weight. Somatostatin levels and smoking had an almost equal influence on the variation in birth weight (approximately 10%). It is suggested that low maternal somatostatin levels are related to an efficient storage of nutrients in the fetoplacental unit, thereby leading to a high birth weight.

Placental hormones and maternal glucose metabolism. A study of fetal growth in normal pregnancy

The interrelations between three placental hormones (oestradiol, progesterone and hPL), maternal glucose metabolism, maternal anthropometry and fetal growth were studied in a sample of 52 carefully selected pregnant women. A relation was found between infant birthweight and both fasting blood glucose and t1/2 of glucose of an intravenous glucose tolerance test at week 37 of pregnancy. The serum concentrations of the placental hormones were not significantly related to the glucose variables. The correlation between birthweight and the maternal levels of hPL in late pregnancy (r = 0.60) persisted when fasting blood glucose and t1/2 of glucose were taken into account. Maternal fat mass was found to explain more of the variation in basal insulin levels around week 37 than did the placental hormones.

Genetic and environmental variation in the birth weight of twins

Two novel approaches to the analysis of twin data are illustrated with data from birth weight in twins. First, two possible covariates of birth weight are fitted to the data simultaneously, allowing for linear effects of these variables, and their correlation. Second, information on chorionicity is used to estimate the effects of chorion type on birth weight. The data were collected from a large sample of twins born in East Flanders, Belgium. Variation and covariation in twins were considered as a function of sex, chorionicity, maternal age, gestational age, and genotype. No evidence for sex differences in causes of variation was found. As expected, the largest source of variation in bith weight was associated with gestational age. Other common environmental influences were non-significant. Heritability was significant, constituting approximately 40% of variation not associated with maternal and gestational age. A small but significant effect of chorionicity was found, such that dichorionic twins show a greater similarity than monochorionic.

Constrained and unconstrained fetal growth: associations with some biological and pathological factors

Data are presented on the birthweights of 1092 siblings and 5207 maternal and paternal relatives of 986 probands. Previous analyses had demonstrated the potency of a maternal regulator constraining fetal growth. Different patterns of birthweights were found in families ascertained, respectively, through very large and very small babies (Ounsted, Scott and Ounsted 1986). When the data were reanalyzed in respect of other biological and pathological factors affecting fetal growth rate the following findings emerged: (1) When pathological factors were associated with the proband pregnancy the typical patterns of pedigree birthweights were not so clearly manifest; (2) general associations were found between the mothers' own birthweights and their size as adults; (3) low maternal birthweight was the biological factor showing the highest risk associated with small babies. When the babies were large the risks associated with high maternal adult weight and parity were similar to those associated with high birthweight. Paternal factors also made a contribution to fast fetal growth rate when pathological factors were absent. These findings confirm our hypothesis that at the lower extreme of fetal growth rate maternal constraint is pre-potent. At the upper extreme, relaxation of constraint allows other biological factors to take up more of the variance.

Maternal fat stores and fat accretion during pregnancy in relation to infant birthweight

Maternal fat stores and fat accretion during pregnancy were estimated from body weight and skinfold thicknesses and by the factorial method in a sample of 56 Swedish women in their second pregnancies who gave birth to singletons at term. Prepregnancy lean body mass, and not fat mass, were strongly correlated with infant birthweight. Total weight gain was significantly correlated with infant birthweight. A wide range of maternal fat accretion during pregnancy was observed, and the amount of fat accumulated was related to the total weight gain. In spite of this, maternal fat accretion during pregnancy was found to have little bearing on the infant birthweight at term.

Relative effect of parental birth weight on infant birth weight at term

The relations between some hereditary and environmental factors and the variation in infant birth weight were estimated by multiple linear regression analyses on a sample of 276 Scandinavian single term pregnancies. Gestational age explained 10.9%, fetal factors (maternal and paternal birth weights and fetal sex) 7.9%, maternal factors (parity, pre-pregnancy weight and height) 5.5% and external factors (adjusted weight gain and smoking) 5.8% of the variation in infant birth weight. It is concluded that maternal and paternal birth weights are rather poor predictors of infant birth weight. Together they explain only 5.6% of the variation in infant birth weight at term.

Stabilizing selection in man: the effect of mother's age on birthweight variance

In order to study the effect of mother's age on birthweight variance, data were collected from Official Vital Statistics of the USA, Japan and Italy. Birthweight means and variances were calculated for all single births and for live births only. The results demonstrated that birthweight variance regularly increases in babies born to mothers of increasingly older age (with the exception of the youngest mothers). Moreover, the higher the variance in all births, the more the variance diminishes after late fetal selection. Therefore, a feedback phenomenon takes place in the stabilizing component of selection, i.e. the difference between the variance of all births and that of live births. As a consequence, at least part of the higher number of fetal losses experienced by older mothers can be attributed to the increased birthweight variance of their children.

Mother's and father's birthweight as predictors of infant birthweight

Mothers' and fathers' birthweights are each significantly related to their infants' birthweight, even after control for 31 potentially confounding variables. The relationship is stronger for mothers and daughters than for other parent-offspring pairs. Parents' birthweights together account for 2% of the variance in sons', and 5% of the variance in daughters' birthweights. There are interactions of maternal birthweight with maternal adult weight, pregnancy weight gain, and parity; the predicted effect of maternal birthweight on infant birthweight is enhanced when the mother weighs more, gains more weight during pregnancy, or is multiparous. Race and parents' drinking and smoking also modify the predicted effect of parents' birthweights. The correlation between mother and offspring birthweights has been attributed to the mother's own uterine experience and its effect on her later reproductive performance. However, the significant relationship of father and infant birthweights reported in this paper suggests that the fetal genes also play some role in determining size at birth.

Sibling similarity in development of covariation among physical traits in early childhood

We studied the sibling similarity in development of covariation among body size characters (body weight (W), body length (S) and head circumference (HC) in Tel Aviv infants from birth up to 2 years of age. We investigated the effects of parental geographic origin, profession, age, current residence, and of family size. Multiple regression analysis with "dummy" procedure established that none of these variables had any significant effect on the aforementioned anthropometric traits. The matrices of phenotypic and genetic correlations, based on sibling similarity data, among age-specific W, S, and HC (measured for 12 different ages) were subjected to principal component analysis in order to elucidate patterns over the age groups. The patterns of both analyses, phenotypic and genetic, were quite similar: one factor in each (first genetic and second phenotypic) had a high positive correlation with early, first 2-3 months of life, W, S, and HC. Three other extracted factors correlated strongly, each with late W, S, and HC, respectively. The results of additional principal component analyses of age-specific W, S, and HC matrices separately, indicate the possibility of existence of two genetic subsystems, the first determining early postnatal stages of human ontogeny, and the second, later phases of child development.

Dizygotic twinning, birth weight and latitude

In Europe and the USA, both mean birth weight and age-standardized dizygotic twinning rates correlate positively and significantly with latitude. It seems possible that these two sorts of correlation have explanations in common via pituitary action. Factors which may be responsible for such action are total consumption of food and consumption of specific items of diet, for example, milk products and potatoes. Lastly, one might wonder whether the association of photoperiodicity with latitude is relevant.