Objective
The purpose of this study was to investigate the association between large-for-gestational-age (LGA) infants and the development of childhood obesity in an inner-city primarily African American population.
Study Design
Maternal, neonatal, socioeconomic, and nutritional histories were collected for mothers with children who were 2-5 years old. Associations between Alexander and customized birthweight percentiles and body mass index for the age of the child were examined.
Results
One hundred ninety-five mother-child pairs were enrolled; the childhood obesity rate was 18%. Increasing Alexander and customized birthweight percentiles were related to increasing obesity. LGA newborn infants were 2.5 times more likely to be obese in childhood than average size newborn infants. Maternal smoking was also associated with childhood obesity.
Conclusion
LGA infants have the highest likelihood of childhood obesity in this inner-city predominantly African American population. Customized growth percentiles perform best in the identification of the highest risk population.
Obesity has increased to and remained at epidemic levels in recent years around the world and specifically in the United States, where adult obesity rates are >30% in all adult subgroups and >45% in non-white women. Perhaps even more concerning are the rising rates of childhood obesity in the United States; so much so that this has become a focus of public health initiatives, including First Lady Michelle Obama’s recently unveiled “Let’s Move” campaign against childhood obesity. Although these initiatives are critical in the fight against childhood obesity, growing evidence regarding the association between birth outcomes and risks of future obesity may lead some of the focus to shift to the impact of pregnancy on these concerning outcomes.
Knowledge of the relationship between in utero exposures and early infant outcomes with later adult morbidities is not new. An association between small-for-gestational-age infants and adult morbidities (such as hypertension, type II diabetes mellitus, and cardiovascular disease) was first proposed by Barker et al after large epidemiologic studies and has been validated in some subsequent work. Increasing relationship of birthweight to childhood obesity has also been noted in several studies. Our objective in this study was to determine the current levels of childhood obesity in an inner-city African American population and to evaluate whether an association exists between large-for-gestational-age (LGA) infants and childhood obesity and overweight. We went further by using a previously validated customized growth percentile model to control for additional confounders to best elucidate those infants who are truly overgrown and who, we believe, are at the highest risk.
Materials and Methods
This was a longitudinal case-control study that consisted of obese (cases) and normal-weight children (control subjects) who were 2-5 years old. Mothers who attended the well-child clinics of Children’s Hospital of Michigan with children between the ages of 2 and 5 years old were identified and enrolled beginning in January 2009. The child’s records were reviewed and his/her height, weight, and other pertinent clinical data were recorded. In addition, the mother was asked to complete an extensive questionnaire that assessed data that was not found consistently in the prenatal chart that included maternal marital and education status, nutrition, prepregnancy exercise frequency, economic and employment status, use of WIC (women, infants, and children federally funded support) or food stamps, and substance misuse history and an extensive nutrition history of the infant/child. Finally, maternal delivery and prenatal records were reviewed for pertinent pregnancy and delivery data. Patients who did not deliver at 1 of 4 hospitals that were included in the study (Hutzel Women’s Hospital, Sinai-Grace Hospital, Henry Ford Hospital, and St. John Riverview Hospital) were excluded. Additional exclusion criteria included those mothers whose delivery records were not available for review and children who were born with major congenital malformations. Institutional review board approval was obtained from the Wayne State University Human Investigation Committee, and permission for review of maternal delivery charts were obtained from the 2 additional hospital systems.
Age- and sex-specific body mass index (BMI) percentiles for each enrolled child were calculated and categorized according to Centers for Disease Control–defined groupings: childhood obesity (BMI for age, ≥95th percentile), overweight (BMI for age, ≥85th to <95th percentile) and healthy weight (BMI for age, >5th to <85th percentile). Underweight children (BMI for age, <5th percentile) were not included in this analysis, because the comparison of interest was the obese group with healthy weight/overweight group. Risk (independent) variables included birthweight percentile subgroups that were defined by the standard Alexander growth curve, which is a US national reference for fetal growth that determines birthweight percentile subgroup by birthweight per gestational age at delivery. Gestational age was obtained from delivery record documentation and generally was determined by last menstrual period and/or first- or second-trimester ultrasound examination. Based on the method of Alexander et al, data was trimmed to exclude birthweight that was inconsistent with gestational age. Additionally, the gestation-related optimal weight (GROW) calculator (available for free download at www.gestation.net ) was used to calculate customized birthweight percentiles. These percentiles are calculated from infant birthweight data that are adjusted for gestational age at delivery, infant gender, maternal height, maternal weight at first prenatal visit, race, and parity and yield an individualized growth trajectory that indicates how much a given fetus is under- or overgrown. The calculated percentiles for both Alexander and GROW percentiles were subgrouped into <10th percentile, 10-50th percentile, 50th-90th percentile, and >90th percentile. Covariates that were evaluated included variables that had been gleaned from the questionnaire and delivery chart and included, but was not limited to, maternal delivery and medical history, socioeconomic factors, and measures of infant feeding.
Pearson χ 2 and 1-way analysis of variance with Student-Newman-Keuls post-hoc comparisons were used to compare maternal characteristics between child BMI groups. Bivariate analyses of the independent variables and covariates vs the 2 dependent variables (childhood obesity and overweight) were performed with the Fisher’s exact test or Pearson χ 2 for categoric variables and the Student t test for continuous variables. To obtain a small group of potential predictors of childhood obesity and overweight outcomes, all factors with a probability value of < .1 were included in logistic regression. A probability value of < .05 in the stepwise logistic regression was considered significant.
Results
At the time of analysis, 195 mother-child pairs who met study criteria were enrolled, and all pertinent data were collected. Thirty-five children (18.3%) were obese; an additional 22 children (11.5%) were overweight. Table 1 gives a comparison of the maternal demographics and clinical characteristics between the 2 groups and the healthy weight group (n = 120). Continuous measures were analyzed with 1-way analysis of variance with Student Newman-Keuls post-hoc comparisons, and categoric variables were analyzed with Pearson χ 2 . No significant differences were noted between groups.
| Maternal characteristic | Obese (n = 35) | Overweight (n = 22) | Healthy weight (n = 120) | P value |
|---|---|---|---|---|
| Maternal age, y a | 24 (15–38) | 23 (16–34) | 22 (15–38) | – |
| Black race, n (%) | 34 (97.1) | 18 (94.7) | 106 (90.6) | .29 |
| Single marital status, n (%) | 30 (85.7) | 20 (90.9) | 108 (90.0) | .55 |
| Nulliparity, n (%) | 19 (54.3) | 12 (54.5) | 53 (44.2) | .40 |
| Gestational age, wk b | 39.3 ± 1.7 | 38.8 ± 2.3 | 38.8 ± 2.6 | .18 |
| Pregnancy weight gain, lbs b | 37.6 ± 17.6 | 36.3 ± 13.7 | 32.2 ± 15.7 | .25 |
| Body mass index at delivery, kg/m 2 b | 35.4 ± 9.3 | 36.0 ± 7.4 | 32.6 ± 7.3 | .09 |
| Smoking during pregnancy, n (%) | 10 (28.6) | 4 (18.2) | 17 (14.2) | .12 |
| Fast food servings/d during pregnancy, n b | 1.2 ± 1.6 | .75 ± .73 | .94 ± 1.1 | .59 |
a Data are given as median (range);
Birthweights for the obese group were evaluated. Increasing birthweight by Alexander percentiles and by customized growth percentiles with the use of the GROW calculator was related to increasing obesity at ages 2-5 years ( Figure ). Of 75 independent variables and covariates, 6 variables (that included Alexander, >90th percentile; GROW, >90th percentile, which reflected fetal growth) and 4 covariates (smoking during pregnancy, number of fruit servings daily during pregnancy, number of vegetable servings daily during pregnancy, and number of servings of juice imbibed daily by the child) had a probability value of < .1 in a bivariate setting. These 6 variables were entered into a stepwise logistic regression ( Table 2 ). Only the GROW >90th percentile and maternal smoking were significant determinants of childhood obesity at age 2-5 years; jointly, they explained 14% of the variance in childhood obesity. The GROW percentile ( R 2 = 0.106) contributed over twice the variance that smoking did ( R 2 square = 0.034). Interactions were not significant. Newborn infants who were <10th percentile in the GROW customized growth percentile had an odds ratio of 0.25 (95% confidence interval, 0.08–0.8) for childhood obesity, compared with the entire group; those infants with a >90th percentile in the GROW customized growth percentile had an odds ratio of 2.5 (95% confidence interval, 1.001–6.2) for childhood obesity. In other words, for babies who were underweight at birth (small for gestational age), the risk for childhood obesity was one-fourth that of the average size newborn infant, but LGA newborn infants were 2.5 times as likely as average to be obese in childhood.
