John H. Himes

A united states national reference for fetal growth

Objective To develop a current national fetal growth curve that can be used as a common reference point by researchers to facilitate investigations of the predictors and consequences of small and large for gestational age delivery. Methods Single live births to United States resident mothers in 1991 (n = 3,134,879) were used for the development of this curve, which was compared with four previously published fetal growth curves. Techniques were developed to address cases with implausible birth weightgestational age combinations and to smooth fetal growth curves across gestational age categories. Results In general, the previously published fetal growth curves underestimated the 1991 United States reference curve. This underestimation is most apparent during the latter weeks of gestation, approximately 33–38 weeks. Conclusion Our findings indicate that the prevalence of fetal growth restriction (FGR) will vary markedly, depending on the fetal growth curve used. Furthermore, many previously published fetal growth curves no longer provide an up-to-date reference for describing the distribution of birth weight by gestational age and for determining FGR that is consistent with the most recent live birth data for the entire United States.

Assessment of Child and Adolescent Overweight and Obesity

Accurate appropriate assessment of overweight and obesity in children and adolescents is a critical aspect of contemporary medical care. However, physicians and other health care professionals may find this a somewhat thorny field to enter. The BMI has become the standard as a reliable indicator of overweight and obesity. The BMI is incomplete, however, without consideration of the complex behavioral factors that influence obesity.Because of limited time and resources, clinicians need to have quick, evidence-based interventions that can help patients and their families recognize the importance of reducing overweight and obesity and take action. In an era of fast food, computers, and DVDs, it is not easy to persuade patients to modify their diets and to become more physically active. Because research concerning effective assessment of childhood obesity contains many gaps, this report is intended to provide a comprehensive approach to assessment and to present the evidence available to support key aspects of assessment. The discussion and recommendations are based on >300 studies published since 1995, which examined an array of assessment tools. With this information, clinicians should find themselves better equipped to face the challenges of assessing childhood overweight and obesity accurately.

Pregnancy complications and birth outcomes in obese and normal-weight women: Effects of gestational weight change

Objective To compare the pregnancy course and outcomes in obese and normal-weight women and their associations with gestational weight change. Methods Multivariate logistic regression described the relation of weight change to pregnancy course and outcomes in a retrospective study of 683 obese and 660 normal-weight women who delivered singleton living neonates. Results Compared with normal-weight women, obese women gained an average of 5 kg (11 Ib) less during pregnancy and were more likely to lose or gain no weight (11% versus less than 1%). Obese women were significantly more likely to have pregnancy complications, but the incidence of complications was not associated with weight change. Compared with obese women who gained 7–11.5 kg (15–25 lb), obese women who lost or gained no weight were at higher risk for delivery of infants under 3000 g or small for gestational age infants, and those who gained more than 16 kg (35 lb) were at twice the risk for delivery of infants who were 4000 g or heavier. Conclusion Gestational weight change was not associated with pregnancy complications in obese or normal-weight women. To optimize fetal growth, weight gains of 7–11.5 kg (15–25 lb) for obese women and 11.5–16 kg (25–35 lb) for normal-weight women appear to be appropriate.

1994-1996 U.S. Singleton Birth Weight Percentiles for Gestational Age by Race, Hispanic Origin, and Gender

Objectives: Establishing and comparing race, ethnic, and gender-specific birth weight percentiles for gestational age is requisite for investigating the determinants of variations in fetal growth. In this study, we calculate percentiles of birth weight for gestational age for the total 1994–1996 U.S. population and contrast these percentiles by racial/ethnic and gender groups. Methods: Single live births to U.S. resident mothers were selected from the 1994–1996 U.S. Natality Files. After exclusions, 5,973,440 non-Hispanic Whites, 1,393,908 non-Hispanic African Americans, 1,683,333 Hispanics, 80,187 Native Americans, and 510,021 other racial/ethnic groups were used to calculate distribution percentiles of birth weight for each gestational age for which there were at least 50 cases to calculate the 50th percentile and 100 cases to calculate the 10th percentile. Results: Fetal growth patterns among the four U.S. racial/ethnic groups varied markedly and, across the gestational age range, there was considerable oscillation in the relative ranking of any one groups birth weight percentile value in comparison to the others. Males had relatively higher birth weight percentile values than females. The proportion of infants with a birth weight value less than 1994–1996 U.S. populations 10th percentile value of birth weight for their corresponding gestational age was 7.87 for non-Hispanic Whites, 15.43 for non-Hispanic African Americans, 9.30 for Hispanics, and 8.81 for Native Americans. Conclusions: While the factors underlying trends and population subgroup differences in fetal growth are unclear, nutrition, smoking habits, health status, and maternal morbidity are possible precursors for part of the variations in patterns of fetal growth. As prenatal care has been touted as a means to reduce the risk of fetal growth restriction at term, assuring the availability and accessibility of comprehensive prenatal care services is viewed as an essential corollary in the effort to improve fetal growth patterns in the United States.

Prevalence of obesity in American Indians and Alaska Natives.

Obesity is an important risk factor for cardiovascular diseases and non-insulin-dependent diabetes, which are chronic diseases that afflict American Indians and Alaska Natives today. Because American Indians are not represented in most national health and nutrition surveys, there is a paucity of data on actual prevalence of obesity in American Indians. We estimated prevalence of overweight and obesity for American Indian adults, school-age children, and preschool children from existing data. The prevalence of obesity in adults was estimated from self-reported weights and heights obtained from a special survey of American Indians performed as part of the 1987 National Medical Expenditure Survey. Prevalence of obesity in American Indians was 13.7% for men and 16.5% for women, which was higher than the US rates of 9.1% and 8.2%, respectively. Obesity rates in American Indian adolescents and preschool children were higher than the respective rates for US all-races combined.

Challenges of Accurately Measuring and Using BMI and Other Indicators of Obesity in Children

BMI is an important indicator of overweight and obesity in childhood and adolescence. When measurements are taken carefully and compared with appropriate growth charts and recommended cutoffs, BMI provides an excellent indicator of overweight and obesity that is sufficient for most clinical, screening, and surveillance purposes. Accurate measurements of height and weight requirethat adequate attention be given to data collection and management. Choosing appropriate equipment and measurement protocols and providing regular training and standardization of data collectors are critical aspects that apply to all settings in which BMI will be measured and used. Proxy measures for directly measured BMI, such as self-reports or parental reports of height and weight, are much less preferred and should only be used with caution and cognizance of the limitations, biases, and uncertainties attending these measures. There is little evidence that other measures of body fat such as skinfolds, waist circumference, or bioelectrical impedance are sufficiently practicable or provide appreciable added information to be used in the identification of children and adolescents who are overweight or obese. Consequently, for most clinical, school, or community settings these measures are not recommended for routine practice. These alternative measures of fatness remain important for research and perhaps in some specialized screening situations that include a specific focus on risk factors for cardiovascular or diabetic disease. Pediatrics 2009;124:S3-S22

Oxidative Stress and Insulin Resistance The Coronary Artery Risk Development in Young Adults study

OBJECTIVE Although cumulative evidence suggests that increased oxidative stress may lead to insulin resistance in vivo or in vitro, community-based studies are scarce. This study examined the longitudinal relationships of oxidative stress biomarkers with the development of insulin resistance and whether these relationships were independent of obesity in nondiabetic young adults. RESEARCH DESIGN AND METHODS Biomarkers of oxidative stress (F2-isoprostanes [F2Isop] and oxidized LDL [oxLDL]), insulin resistance (the homeostasis model assessment of insulin resistance [HOMA-IR]), and various fatness measures (BMI, waist circumference, and estimated percent fat) were obtained in a population-based observational study (Coronary Artery Risk Development in Young Adults) and its ancillary study (Young Adult Longitudinal Trends in Antioxidants) during 2000–2006. RESULTS There were substantial increases in estimated mean HOMA-IR over time. OxLDL and F2Isop showed little association with each other. Mean evolving HOMA-IR increased with increasing levels of oxidative stress markers (P < 0.001 for oxLDL and P = 0.06 for F2Isop), measured in 2000–2001. After additional adjustment for adiposity, a positive association between oxLDL and HOMA-IR was strongly evident, whereas the association between F2Isop and HOMA-IR was not. CONCLUSIONS We observed positive associations between each of two oxidative stress markers and insulin resistance. The association with oxidized LDL was independent of obesity, but that with F2Isop was not.

Reference curves for triceps and subscapular skinfold thicknesses in US children and adolescents

BACKGROUND Skinfold thicknesses have long been considered important and valid measurements of subcutaneous fat. Nevertheless, there are no current skinfold reference data for US children and adolescents. OBJECTIVE We developed new percentile reference curves for triceps and subscapular skinfold thicknesses by using the same national samples as those included in the reference curves for body mass index (BMI) in the Centers for Disease Control and Prevention 2000 Growth Charts. DESIGN We included triceps and subscapular skinfold-thickness measurements for 32,783 individuals who also had complete data for BMI. The LMS method was used to derive 10 smoothed skinfold-thickness percentile reference curves and to generate the L, M, and S parameters that allow the calculation of standardized z scores. RESULTS The new reference curves exhibit established age- and sex-related patterns of development, including dramatic prepubescent increases in subcutaneous fatness in boys at the highest percentiles. Comparisons of smoothed medians for race-ethnicity groups confirm greater subcutaneous fatness in white children than in black age mates at the triceps site but similar median subscapular skinfold thicknesses. Median skinfold thicknesses for children considered overweight (> or =85th percentile) or obese (> or =95th percentile) on the basis of BMI cutoffs do not follow closely the skinfold percentile reference channels across age, especially in boys, which suggests a certain degree of independence between BMI and skinfold thickness at the upper extremes of the BMI distribution. CONCLUSIONS The age- and sex-standardized skinfold percentiles and z scores will be appropriate for a wide range of research applications that consider measures of subcutaneous fat. Because they were developed by using the same children as those used for the 2000 BMI curves of the Centers for Disease Control and Prevention, they provide an important new complementary assessment tool that should be appropriate for almost all US children and adolescents.

Validity and reliability of self-reported stature and weight of US adolescents

Validity and reliability of self‐reported stature and weight were investigated for U.S. adolescents (12.0–17.0 years) who were participants in the Third National Health and Nutrition Examination Survey (NHANES III). Data were collected on 1,635 youth and were statistically weighted to represent the national population. Self‐reported weights are missing from 40% of 12 year olds and 25% of 13 year olds. Those who refused or were unable to provide self‐reported weights were younger, shorter, and lighter than those who did. Among those who provided self‐reports, the average bias and random error in reporting were largest for the youngest youth. Biases in reporting stature and weight were consistently negative following the NHANES III protocol. The intraclass coefficients between measured and self‐reported dimensions within age and gender groups ranged from 0.57 to 0.91 and from 0.85 to 0.98, for stature and weight, respectively. Self‐reported stature and weight are not recommended as proxies for measured dimensions for youth less than 14 years of age. Am. J. Hum. Biol. 13:255–260, 2001.

Early body size and subsequent weight again as predictors of breast cancer incidence (Iowa, United States)

We examined whether associations of adult weight gain with the risk of postmenopausal breast cancer vary by stature, waist-hip ratio (WHR), and early adult size in a cohort of 37,105 Iowa (United States) women. Both low body mass index (kg/m2) (BMI) at age 18 and high subsequent weight-gain were associated independently with increased risk of incident postmenopausal breast cancer. After stratifying on BMI at age 18, high weight gain was associated with increased risk irrespective of whether early BMI was low (relative risk [RR]=1.92, 95 percent confidence interval [CI]=1.45–2.53) or high (RR=1.59, Ci=1.19–2.12). Women with lower BMI at 18 were at a higher risk at all levels of weight change, but having low BMI at age 18 and low subsequent weight gain conferred no significantly excess risk over those with high BMI at 18 and low gain. An inconsistent increase in risk was associated with taller stature; there was no additional risk associated with high WHR. Part of the observed risk from lower early size may reflect greater weight gain by lighter women. Limiting adult weight gain thus may be a feasible method to avoid increasing an individuals risk of breast cancer. Reasons for different effects of early cf late weight gain are not established, but benefits of a greater size at age 18 are likely to be offset by increased risks of other weight-related diseases at older ages.