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Medical Research Council Epidemiology Resource Centre (C.R.G., M.K.J., S.M.R., K.M.G., C.C.), University of Southampton, Southampton SO16 6YD, United Kingdom; and Centre for Paediatric Epidemiology and Biostatistics (C.M.L.), Institute of Child Health, University College London, London WC1N 1EH, United Kingdom
Address all correspondence and requests for reprints to: Catharine Gale, MRC Epidemiology Resource Centre, Southampton General Hospital, Southampton SO16 6YD, United Kingdom. E-mail: crg{at}mrc.soton.ac.uk.
| Abstract |
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Objective: Our objective was to examine the relation between maternal size in pregnancy, early growth and body composition in children.
Design and Setting: We conducted a prospective cohort study in Southampton, United Kingdom.
Participants: Participants included 216 9-yr-old children whose mothers had participated in a study of nutrition during pregnancy.
Main Outcome Measures: Fat mass and lean mass were measured by dual-energy x-ray absorptiometry and adjusted for height (fat mass index and lean mass index).
Results: Fat mass index at age 9 yr was greater in children whose mothers had a larger mid-upper arm circumference in late pregnancy or a higher prepregnant body mass index. For 1 SD increase in maternal mid-upper arm circumference in late pregnancy, fat mass index rose by 0.26 [95% confidence interval (CI) 0.06–0.46] SD in boys and by 0.44 (95% CI 0.31–0.57) SD in girls. For 1 SD increase in maternal prepregnant BMI, fat mass index rose by 0.26 (95% CI 0.04–0.48) SD in boys and by 0.42 (95% CI 0.29–0.56) SD in girls.
Conclusions: Mothers with a higher prepregnant body mass index or a larger mid-upper arm circumference during pregnancy tend to have children with greater adiposity at age 9. The extent to which this is attributable to genetic factors, the influence of maternal lifestyle on that of her child, or maternal adiposity acting specifically during pregnancy on the childs fat mass cannot be determined in this study.
| Introduction |
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There is considerable evidence that infancy and early childhood are important periods for determining future risk of obesity. Infants who are at the highest end of the weight or body mass index (BMI) distribution or who grow rapidly in the first 2 yr of life are at increased risk of subsequent obesity (8). Recent findings that rapid weight gain in infancy and between the ages of 3 and 6 yr predict increased adiposity in young adults imply that the changes in body composition linked with faster early weight gain may be long term (9). Evidence from several systematic reviews suggest that breastfeeding may protect against later obesity, possibly by slowing weight gain in infancy (10, 11), although there are few data on its relation with direct measures of childhood adiposity, such as those obtained by dual-energy x-ray absorptiometry (DXA) (12).
The importance of the prenatal environment in influencing later obesity is still unclear. Although many studies have shown associations between high birth weight and greater BMI in later life (13), birth weight provides only a crude indicator of prenatal experience, and BMI depends on both fat and lean tissue mass so may provide a misleading indicator of adiposity (14). In studies of children and adolescents using direct measurements of body composition, increased birth weight is associated with greater lean mass but not with fat mass (15, 16). New research, however, suggests that childrens adiposity may be influenced by their mothers own fatness during pregnancy. Few studies have examined the long-term consequences of maternal overnutrition on fat mass in the offspring (17). Some evidence of its potential effect has come from an Australian cohort where a higher maternal BMI before pregnancy was linked with a raised BMI in the offspring at age 14 (18), but BMI cannot differentiate between lean and fat mass. In a study of women with normal glucose tolerance levels, those who were overweight or obese in pregnancy had offspring with increased fat mass at birth (19). If this relation persists into later childhood, it could have important implications for preventing obesity.
We investigated the relations between maternal size in pregnancy, early growth and body composition at the age of 9 yr in a cohort of children whose mothers had participated in a study of nutrition during pregnancy.
| Subjects and Methods |
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When these children approached age 9 yr, we wrote to the parents of those still living in Southampton inviting the children to participate in another study. Of 461 invited, 216 (47%) agreed to attend a clinic. Height was measured using a stadiometer and weight using digital scales (SECA model no. 835). The children underwent measurements of body composition by DXA (Lunar DPX-L instrument using specific pediatric software, version 4.7c; GE Corp., Madison, WI). The instrument was calibrated every day, and all scans were done with the children wearing light clothing. The short-term and long-term coefficients of variation of the instrument were 0.8 and 1.4%, respectively.
Statistical analysis
Fat mass and lean mass were adjusted for height by calculating fat mass index and lean mass index. After log-log regression analysis (24), fat mass index was calculated as total body fat (kilograms)/height (meters)n and lean mass index as total lean body mass (kilograms)/height (meters)n where the power of n was 4.9 (fat mass index) and 2.2 (lean mass index), respectively. These values of n are those that gave the least correlation between the respective indices and height. To examine the influence of infant growth with the effect of birth weight removed, we created a conditional infant weight gain variable, unrelated to birth weight, by using linear regression with weight at age 9 months as the dependent variable and birth weight as the independent variable and saving the standardized residuals. All anthropometric variables for mother and child are expressed as SD scores (SDS), which were internally referenced and calculated for each sex separately. Birth weight SDS were adjusted for gestational age at birth.
We used t or
2 tests to examine the characteristics of the participants at the 9-yr follow-up. Linear regression was used to examine the relation between maternal and child characteristics and fat mass and lean mass indices, adjusting for age at examination. Where necessary, variables were transformed using logarithms to satisfy statistical assumptions of normality.
The Local Research Ethics Committee approved the study. The children and their parents gave written informed consent.
| Results |
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In age-adjusted linear regression analyses of boys and girls separately, fat mass index tended to be greater in children whose mothers had a larger mid-upper arm circumference in late pregnancy or a greater prepregnant BMI (Table 3
). Lean mass index tended to be greater in those whose mothers had a larger mid-upper arm circumference or a greater prepregnant BMI. We found no significant associations in either sex between fat or lean mass indices and maternal height or the amount of weight women gained during pregnancy, whether expressed as a continuous variable or examined according to Institute of Medicine categories. In boys, but not in girls (P for interaction term = 0.018), lean mass index was greater in those who had weighed more at birth. There was a similar, although weaker, association in boys between lean mass index and weight at age 9 months, although weight gain by 9 months conditional on birth weight was not associated with lean mass index. Maternal smoking either in early or late pregnancy was associated with a lower lean mass index in boys. In girls, these relations were weaker, although interaction terms were not statistically significant. In girls only, being breastfed for over 4 months was associated with significant reductions in fat mass index compared with children who were never breastfed. No such relation was seen in boys (P for interaction term = 0.03). There were no statistically significant associations in either sex between body composition and maternal social class, educational qualifications, or exercise during pregnancy (data not shown).
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In boys, other independent predictors of a greater fat mass index at age 9 yr were greater conditional weight gain by age 9 months and being exposed to maternal smoking in pregnancy. The relation in boys between lean mass and maternal smoking in pregnancy ceased to be statistically significant in multivariate analysis due to adjustment for birth weight. In girls, being breastfed for over 4 months remained a significant independent predictor of a lower fat mass index compared with girls who were never breastfed. In both sexes, greater lean mass index at age 9 yr was associated with higher birth weight, although this relation was of borderline significance in girls. In total, 15 children had a birth weight of less than 2.5 kg. There were weak inverse associations of borderline significance between low birth weight and both maternal prepregnant BMI and mid-upper arm circumference in late pregnancy. In sex-adjusted analyses, low birth weight was associated with lower lean mass index at age 9 yr (–0.50; 95% CI –0.95 to –0.05 SD) but was not associated with fat mass index.
Exclusion of children who were premature (n = 16) or whose mothers had preeclampsia during pregnancy (n = 16) had little effect on the results.
We found no associations in the multivariate analyses between the height-adjusted fat or lean mass indices and maternal weight gain in pregnancy, whether expressed as a continuous variable (shown in Table 4
) or as the Institute of Medicine weight gain categories (data not shown). However, there was evidence that women who put on an excessive amount of weight in pregnancy, according to the Institute of Medicine weight gain categories, had a considerably larger mid-upper arm circumference in late pregnancy, itself a strong predictor of fat mass in the child. Compared with women whose weight gain was inadequate during pregnancy, women whose weight gain was excessive had a mid-upper arm circumference in late pregnancy that was 0.95 (95% CI 0.65–1.24) SD higher (P < 0.0001). To gauge whether the associations found here between mid-upper arm circumference in late pregnancy and fat mass index in the child were dependent on those children whose mothers gained an excessive amount of weight during pregnancy, we repeated our analysis removing these individuals. This exclusion had little effect.
In summary, fat mass index was greater in children whose mothers had a larger mid-upper arm circumference in late pregnancy or a higher prepregnant BMI (Fig. 1
). Other independent predictors of greater fat mass were smoking in pregnancy and greater conditional weight gain in infancy (in boys) and not being breastfed (in girls). Lean mass was greater in children who had weighed more at birth.
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| Discussion |
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One explanation for these findings may be genetic. Evidence from twin studies suggest that genetic influences account for some of the phenotypic variation in BMI (25) and percent body fat (26). Another explanation may lie in the maternal metabolic environment during pregnancy. Women who are overweight or obese before conception have been shown to experience a marked decrease in insulin sensitivity during pregnancy (27). This results in greater availability of lipids and glucose for the fetus and could lead to higher fetal concentrations of insulin (28, 29) and leptin (30, 31). Fetuses with higher cord concentrations of insulin and leptin tend to have a higher fat mass at birth (32, 33). The long-term effects on offspring adiposity of exposure to maternal overnutrition during pregnancy are not yet clear, but there is some evidence from experimental studies in animals to suggest that increases in fetal nutrient supply may influence the development of appetite regulation and adipocyte metabolism (31).
The mean prepregnancy BMI of the mothers in this study, recruited in 1991–1992, was 22.7 kg/m2, similar to that found in a prospective study of pregnancy in Australia where women were recruited between 1981 and 1984 (18). However, rates of obesity among women at the start of pregnancy have increased markedly in recent years (34, 35). Contemporary cohorts of pregnant women contain far higher proportions of women who are overweight or obese at the start of pregnancy (23) than our comparatively healthy sample.
Although evidence from several systematic reviews suggests that breastfeeding may protect against later obesity (10, 11), the few studies that have examined its relation with direct measures of childhood adiposity, obtained by DXA, found no statistically significant associations (12, 36). In the present study, we found that girls who had been breastfed for over 4 months had significantly lower fat mass at the age of 9 yr than those who were never breastfed, but no such relation was present in boys. Although in these data, there was no association between conditional weight gain in infancy and duration of breastfeeding, there was a trend in girls toward reduced weight gain with increasing duration of breastfeeding. Consistent with other studies (8, 9, 15), we found that children with a lower weight gain in the first 9 months after birth tended to have a lower fat mass at age 9 yr. This association was statistically significant only in boys, but similar, although weaker, trends were seen in girls. Greater weight at birth was associated with higher lean mass at age 9 yr. Similar observations have been reported both in other cohorts of children (37) and in older populations (38, 39).
Although some studies of children have found a higher percent body fat in boys than in girls (40), findings from other studies have found the reverse. In the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort at age 9 (37), Project Heartbeat at age 8 (41), and in studies of 6-yr-old children in Denmark (42) and 8 yr olds in Sweden (43), fat mass and percent body fat were consistently greater in girls than in boys. There was a similar pattern in the present study.
Our study has a number of limitations. First, we are not able to identify with certainty whether the relations we found between measures of maternal size in pregnancy, i.e. prepregnant BMI and mid-upper arm circumference, and fat mass in childhood were in fact due to maternal adiposity during pregnancy. Both measures provide an indicator of nutritional status (22), but they reflect both lean and fat mass. It is also possible that the associations found were due not to maternal nutritional status during pregnancy but rather to maternally transmitted genes or to the influence of the mothers lifestyle and diet on that of her child. Second, our data on weight before pregnancy were self-reported. It is possible that these self-reports may have introduced some inaccuracy into our measures of prepregnant BMI and weight gain during pregnancy. Third, we were unable to follow up all the children in the cohort. Some had moved away from the area, and some declined to participate. Children who took part in the 9-yr follow-up were more likely to have mothers from nonmanual occupational classes, but mean maternal mid-upper arm circumference and BMI were similar in the groups who did and did not participate. We think it unlikely that bias will have been introduced. Another limitation was the size of our study (115 boys and 101 girls). It is possible that the differing strength of some associations between the sexes was due to lack of statistical power. Finally, we had no information on pubertal status. It is possible that the earlier onset of puberty in girls may help to account for the differences in findings by sex.
One explanation for our findings that fat mass in 9-yr-old children was increased in those whose mothers had a greater mid-upper arm circumference in late pregnancy or a higher prepregnant BMI is that maternal overnutrition before and during pregnancy, although not excessive weight gain, may have a long-term, persisting influence on the adiposity of the child. However, maternally transmitted genetic factors and the effect of maternal lifestyle on that of her child could also explain our results. The extent to which the association is due to maternal adiposity acting specifically during pregnancy cannot be determined in this study.
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| Acknowledgments |
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| Footnotes |
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Disclosure Summary: The authors have nothing to declare.
First Published Online August 7, 2007
Abbreviations: BMI, Body mass index; CI, confidence interval; DXA, dual-energy x-ray absorptiometry; SDS, SD score.
Received January 12, 2007.
Accepted July 26, 2007.
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