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

Abstract

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.

Keywords: body mass index; growth; growth charts; nutrition surveys; pediatric obesity; transgender.

Figure 1

Comparison of age-adjusted sex non-specific height curves with CDC 2000 girl and boy age- and sex-adjusted height curves. (A) shows our age-adjusted sex non-specific height curves overlaid on the CDC 2000 girl age- and sex-adjusted height curves, highlighting the 3^rd, 50^th, and 97^th percentiles. (B) shows our age-adjusted sex non-specific height curves overlaid on the CDC 2000 boy age- and sex-adjusted height curve, highlighting the 3^rd, 50^th, and 97^th percentiles. (C) shows our age-adjusted sex non-specific height growth curves. Here, we highlight the 3^rd, 25^th, 50^th, 75^th, and 97^th percentiles given their clinical utility.

Figure 2

Comparison of age-adjusted sex non-specific weight curves with CDC 2000 girl and boy age- and sex-adjusted weight curves. (A) shows our age-adjusted sex non-specific weight curves overlaid on the CDC 2000 girl age- and sex-adjusted weight curves, highlighting the 3^rd, 50^th, and 97^th percentiles. (B) shows our age-adjusted sex non-specific weight curves overlaid on the CDC 2000 boy age- and sex-adjusted weight curve, highlighting the 3^rd, 50^th, and 97^th percentiles. (C) shows our age-adjusted sex non-specific weight growth curves. Here, we highlight the 3^rd, 25^th, 50^th, 75^th, and 97^th percentiles given their clinical utility.

Figure 3

Comparison of age-adjusted sex non-specific body mass index (BMI) curves with CDC 2000 girl and boy age- and sex-adjusted BMI curves. (A) shows our age-adjusted sex non-specific BMI curves overlaid on the CDC 2000 girl age- and sex-adjusted BMI curves, highlighting the 5^th, 50^th, 85^th, and 95^th percentiles. (B) shows our age-adjusted sex non-specific BMI curves overlaid on the CDC 2000 boy age- and sex-adjusted weight curve, highlighting the 3^rd, 50^th, 85^th, and 95^th percentiles. (C) shows our age-adjusted sex non-specific BMI growth curves. Here, we highlight the 5^rd (underweight), 25^th, 50^th, 85^th (overweight), and 95^th (obesity) percentiles given their clinical utility.

Figure 4

Example of a transgender male (assigned female at birth) individual with height plotted on the age-adjusted sex non-specific height curves. (B) shows height plotted on the age-adjusted sex non-specific height curves, while (A) and (C) show height plotted on the CDC 2000 girl and boy height curves, respectively. This individual received pubertal suppression with gonadotropin releasing hormone agonist therapy (pubertal blocker) beginning around age 12 years (↑) and subsequently began receiving testosterone for cross-sex hormonal therapy beginning around age 15 years (↑).

Figure 5

Example of a transgender female (assigned male at birth) individual with body mass index (BMI) plotted on the age-adjusted sex non-specific BMI curves. (B) shows BMI plotted on the age-adjusted sex non-specific BMI curves, while (A) and (C) show BMI plotted on the CDC 2000 girl and boy BMI curves, respectively. This individual received pubertal suppression with gonadotropin releasing hormone agonist therapy (pubertal blocker) beginning around age 13 years (↑) and subsequently began receiving estradiol for cross-sex hormonal therapy beginning around age 15 years (↑). At 17 years old, BMI was in the normal weight category (83rd percentile) on the CDC 2000 girl chart, however, overweight category (86th percentile) on the age-adjusted sex non-specific growth chart.