Sex non-specific growth charts and potential clinical implications in the care of transgender youth

Introduction

The Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) created separate growth charts for girls and boys because growth patterns and rates differ between sexes. However, scenarios exist in which this dichotomizing "girls versus boys" approach may not be ideal, including the care of non-binary youth or transgender youth undergoing transitions consistent with their gender identity. There is therefore a need for growth charts that age smooth differences in pubertal timing between sexes to determine how youth are growing as "children" versus "girls or boys" (e.g., age- and sex-neutral, compared to age- and sex-specific, growth charts).

Methods

Employing similar statistical techniques and datasets used to create the CDC 2000 growth charts, we developed age-adjusted, sex non-specific growth charts for height, weight, and body mass index (BMI), and z-score calculators for these parameters. Specifically, these were created using anthropometric data from five US cross-sectional studies including National Health Examination Surveys II-III and National Health and Nutrition Examination Surveys I-III. To illustrate contemporary clinical practice, we overlaid our charts on CDC 2000 girls and boys growth charts.

Results

39,119 youth 2-20 years old (49.5% female; 66.7% non-Hispanic White; 21.7% non-Hispanic Black) were included in the development of our growth charts, reference ranges, and z-score calculators. Respective curves were largely superimposable through around 10 years of age after which, coinciding with pubertal onset timing, differences became more apparent.

Discussion

We conclude that age-adjusted, sex non-specific growth charts may be used in clinical situations such as transgender youth in which standard "girls versus boys" growth charts are not ideal. Until longitudinal auxological data are available in these populations, our growth charts may help to assess a transgender youth's growth trajectory and weight classification, and expectations surrounding these.

Adjusting for Pubertal Status Reduces Overweight and Obesity Prevalence in the United States

OBJECTIVE

To compare pediatric overweight and obesity prevalence among non-Hispanic white, Mexican American, and non-Hispanic black US youths before and after adjusting body mass index (BMI) for pubertal status, as assessed by Tanner stage.

STUDY DESIGN

We analyzed cross-sectional anthropometric and pubertal data from non-Hispanic white, Mexican American, and non-Hispanic black youths in the National Health and Nutrition Examination Survey (NHANES) III. We developed specialized Tanner stage and chronological age-adjusted models to establish Tanner-stage adjusted BMI z-scores, which were then used to determine adjusted overweight/obesity prevalence. We compared pediatric overweight/obesity prevalence before and after pubertal status adjustment.

RESULTS

Among 3206 youths aged 8-18 years (50% male; 26% non-Hispanic white, 35% Mexican American, 39% non-Hispanic black), adjusting BMI for Tanner stage significantly reduced overweight (males, from 29% to 21%; females, from 29% to 17%) and obesity (males, from 14% to 7%; females, from 11% to 5%) prevalence across all races/ethnicities. The obesity prevalence reduction was more pronounced in Mexican Americans (males, 11% reduction; females, 9% reduction) and non-Hispanic blacks (males and females, 10% reduction) compared with non-Hispanic whites (males, 6% reduction; females, 5% reduction). Similar patterns were seen in overweight prevalence.

CONCLUSIONS

Adjusting for pubertal status reduced the prevalence of overweight/obesity in non-Hispanic white, Mexican American, and non-Hispanic black youth. This suggests that adjusting for puberty incorporates changes otherwise not captured when only considering the age of a child. Adjusting BMI for pubertal status may be important when interpreting a youth's weight status and consideration for obesity management, as well as when interpreting pediatric overweight/obesity prevalence data.

Parental childhood growth and offspring birthweight: pooled analyses from four birth cohorts in low and middle income countries

Objective

Associations between parental and offspring size at birth are well established, but the relative importance of parental growth at different ages as predictors of offspring birthweight is less certain. Here we model parental birthweight and postnatal conditional growth in specific age periods as predictors of offspring birthweight.

Methods

We analyzed data from 3,392 adults participating in four prospective birth cohorts and 5,506 of their offspring.

Results

There was no significant heterogeneity by study site or offspring sex. 1SD increase in maternal birthweight was associated with offspring birthweight increases of 102 g, 1SD in maternal length growth 0–2 year with 46 g, and 1SD in maternal height growth Mid-childhood (MC)-adulthood with 27 g. Maternal relative weight measures were associated with 24 g offspring birth weight increases (2 year- MC) and 49 g for MC-adulthood period but not with earlier relative weight 0–2 year. For fathers, birthweight, and linear/length growth from 0–2 year were associated with increases of 57 and 56 g in offspring birthweight, respectively but not thereafter.

Conclusions

Maternal and paternal birthweight and growth from birth to 2 year each predict offspring birthweight. Maternal growth from MC-adulthood, relative weight from 2-MC and MC-adulthood also predict offspring birthweight. These findings suggest that shared genes and/or adequate nutrition during early life for both parents may confer benefits to the next generation, and highlight the importance of maternal height and weight prior to conception. The stronger matrilineal than patrilineal relationships with offspring birth weight are consistent with the hypothesis that improving the early growth conditions of young females can improve birth outcomes in the next generation. Am. J. Hum. Biol. 27:99–105, 2015. © 2014 The Authors American Journal of Human Biology Published by Wiley Periodicals, Inc.

Inhibin B and luteinizing hormone levels in girls aged 6-11 years from NHANES III, 1988-1994

OBJECTIVE

To evaluate inhibin B and luteinizing hormone (LH) levels in a large, representative cross-sectional sample of US girls and characterize the relationships of these laboratory values with age, clinical signs of puberty and other correlates.

DESIGN

Cross-sectional analysis of LH and inhibin B in banked serum from 720 girls aged 6-11 years who participated in the Third National Health and Nutrition Examination Survey (NHANES III).

MEASUREMENTS

Levels of inhibin B and LH, race, ethnicity and anthropometric measurements were compared for all girls. Visual assessment of pubertal stage was performed on girls aged 8 years and older. A two-part model was used to establish normative data and Tobit regression models were used to evaluate associations with participant characteristics. Receiver operating characteristic (ROC) analysis was performed to identify optimum cut points predictive of puberty onset.

RESULTS

Mean hormone levels progressively increased with age. LH levels progressively increased with pubertal stage. Inhibin B levels increased gradually from breast stage I to II, then more sharply to peak at stage III, followed by a plateau at stages IV and V. ROC curves indicated that both hormones were consistent with pubertal onset as indicated by breast stage II.

CONCLUSIONS

This study characterizes inhibin B and LH values in a large, representative cross-sectional sample of US girls. Inhibin B can be a useful tool in combination with other clinical and biochemical parameters to evaluate gonadal function as a reflection of pubertal progression in girls.

Comparability of skinfold thickness to DXA whole-body total fat in their associations with serum triglycerides in youths

OBJECTIVE

To determine the comparability of triceps and subscapular skinfold thicknesses with dual X-ray absorptiometry (DXA) whole-body total fat (kg) in relation to serum triglyceride (TG) levels and increased risk of elevated TG levels, and identified optimum skinfold cutoffs for screening purposes in US adolescents.

SUBJECTS/METHODS

Data from triceps and subscapular skinfold thickness, DXA whole-body total fat and serum TGs were obtained from 1505 US adolescents ages 12.00-17.99 years, who participated in two continuous National Health and Nutrition Examination Survey (NHANES) cycles 2001-2004. Study associations were examined with linear and logistic models, and ROC (receiver operating characteristic) analyses were used to derive skinfold cutoffs for identifying the risk of elevated TG levels.

RESULTS

Using area under the curves (AUCs) as metrics of prediction accuracy (with bootstrapped 95% CIs), no significant differences were found between skinfolds and DXA logistic models for predicting elevated TG levels. Similarly, skinfold and DXA models had comparable precision in predicting continuous serum TG from bootstrapped root mean squared errors for both sexes. Population-adjusted marginal mean estimates indicated that youths whose skinfolds are in the top quartile had TG levels within 83-108 mg/dl. Skinfold cutoffs for predicting elevated estimated TG using ROC analyses showed that cutoffs decreased with age and ranged from 13 to 30 mm for ages 12-17, in yearly intervals.

CONCLUSION

Skinfold thicknesses were comparable to DXA whole-body total fat in predicting serum TG levels. These skinfold cutoffs could be used in practical settings as a first pass screener for identifying US adolescents at risk of elevated serum TGs.

A two-part model for reference curve estimation subject to a limit of detection

Reference curves are commonly used to identify individuals with extreme values of clinically relevant variables or stages of progression which depend naturally on age or maturation. Estimation of reference curves can be complicated by a technical limit of detection (LOD) that censors the measurement from the left, as is the case in our study of reproductive hormone levels in boys around the time of the onset of puberty. We discuss issues with common approaches to the LOD problem in the context of our pubertal hormone study, and propose a two-part model that addresses these issues. One part of the proposed model specifies the probability of a measurement exceeding the LOD as a function of age. The other part of the model specifies the conditional distribution of a measurement given that it exceeds the LOD, again as a function of age. Information from the two parts can be combined to estimate the identifiable portion (i.e. above the LOD) of a reference curve and to calculate the relative standing of a given measurement above the LOD. Unlike some common approaches to LOD problems, the two-part model is free of untestable assumptions involving unobservable quantities, flexible for modeling the observable data, and easy to implement with existing software. The method is illustrated with hormone data from the Third National Health and Nutrition Examination Survey.