Deep phenotyping of pubertal development in Norwegian children: the Bergen Growth Study 2.

BACKGROUND: The Bergen Growth Study 2 (BGS2) aims to characterise somatic and endocrine changes in healthy Norwegian children using a novel methodology. SUBJECTS AND METHODS: A cross-sectional sample of 1285 children aged 6-16 years was examined in 2016 using novel objective ultrasound assessments of breast developmental stages and testicular volume in addition to the traditional Tanner pubertal stages. Blood samples allowed for measurements of pubertal hormones, endocrine disruptive chemicals, and genetic analyses. RESULTS: Ultrasound staging of breast development in girls showed a high degree of agreement within and between observers, and ultrasound measurement of testicular volume in boys also showed small intra- and interobserver differences. The median age was 10.4 years for Tanner B2 (pubertal onset) and 12.7 years for menarche. Norwegian boys reached a pubertal testicular volume at a mean age of 11.7 years. Continuous reference curves for testicular volume and sex hormones were constructed using the LMS method. CONCLUSIONS: Ultrasound-based assessments of puberty provided novel references for breast developmental stages and enabled the measurement of testicular volume on a continuous scale. Endocrine z-scores allowed for an intuitive interpretation of changing hormonal levels during puberty on a quantitative scale, which, in turn, provides opportunities for further analysis of pubertal development using machine-learning approaches.

Reference Curves for Pediatric Endocrinology: Leveraging Biomarker Z-Scores for Clinical Classifications.

CONTEXT: Hormone reference intervals in pediatric endocrinology are traditionally partitioned by age and lack the framework for benchmarking individual blood test results as normalized z-scores and plotting sequential measurements onto a chart. Reference curve modeling is applicable to endocrine variables and represents a standardized method to account for variation with gender and age. OBJECTIVE: We aimed to establish gender-specific biomarker reference curves for clinical use and benchmark associations between hormones, pubertal phenotype, and body mass index (BMI). METHODS: Using cross-sectional population sample data from 2139 healthy Norwegian children and adolescents, we analyzed the pubertal status, ultrasound measures of glandular breast tissue (girls) and testicular volume (boys), BMI, and laboratory measurements of 17 clinical biomarkers modeled using the established "LMS" growth chart algorithm in R. RESULTS: Reference curves for puberty hormones and pertinent biomarkers were modeled to adjust for age and gender. Z-score equivalents of biomarker levels and anthropometric measurements were compiled in a comprehensive beta coefficient matrix for each gender. Excerpted from this analysis and independently of age, BMI was positively associated with female glandular breast volume (ß = 0.5, P < 0.001) and leptin (ß = 0.6, P < 0.001), and inversely correlated with serum levels of sex hormone-binding globulin (SHBG) (ß = -0.4, P < 0.001). Biomarker z-score profiles differed significantly between cohort subgroups stratified by puberty phenotype and BMI weight class. CONCLUSION: Biomarker reference curves and corresponding z-scores provide an intuitive framework for clinical implementation in pediatric endocrinology and facilitate the application of machine learning classification and covariate precision medicine for pediatric patients.

Low BMI, but not high BMI, influences the timing of puberty in boys.

BACKGROUND: Previous studies investigating the association between weight status and onset of puberty in boys have been equivocal. It is currently unclear to what extent weight class influences puberty onset and progression. OBJECTIVES: To explore the relationship between degree of sexual maturation and anthropometric measures in Norwegian boys. METHODS: The following endpoints were collected in a Norwegian cross-sectional study of 324 healthy boys aged 9-16: ultrasound-determined testicular volume (USTV), total serum testosterone, Tanner pubic hair stage, height, weight, waist circumference (WC), subscapular skinfolds (SSF), and body fat percentage (%BF). Testicular volume-for-age z-scores were used to classify "early," "average," or "late" maturing boys. Ordinal logistic regression analyses with a proportional odds model were applied to analyze the association between anthropometric variables and age-adjusted degree of pubertal development, with results expressed as age-adjusted odds ratios (AOR). Cumulative incidence curves for reaching pubertal milestones were stratified by BMI. RESULTS: Boys with a low BMI for age (BMIz  < -1) were less likely to have reached a pubertal testicular volume (USTV ≥ 2.7 mL) or a pubertal serum level of testosterone (≥0.5 nmol/L) compared to normal weight boys (AOR 0.3, p = 0.038, AOR 0.3, p = 0.026, respectively), and entered puberty on average with a delay of approximately eight months. Boys with high BMI for age (BMIz  > 1) exhibited a comparable timing as normal weight boys. The same was found for WC. Pubertal markers were not associated with SSF or %BF. CONCLUSION: By examining the association between puberty and weight status classified as low, average, or high, we found that a low BMI or WC for age were associated with a less advanced pubertal development and delayed timing of puberty in boys. No significant association was observed for a high BMI or WC. Moreover, no significant effects of SSF or %BF were observed. A low weight status should also be considered when assessing pubertal development in boys.

Hormone References for Ultrasound Breast Staging and Endocrine Profiling to Detect Female Onset of Puberty.

CONTEXT: Application of ultrasound (US) to evaluate attainment and morphology of glandular tissue provides a new rationale for evaluating onset and progression of female puberty, but currently no hormone references complement this method. Furthermore, previous studies have not explored the predictive value of endocrine profiling to determine female puberty onset. OBJECTIVE: To integrate US breast staging with hypothalamic-pituitary-gonadal hormone references and test the predictive value of an endocrine profile to determine thelarche. DESIGN SETTING AND PARTICIPANTS: Cross-sectional sample of 601 healthy Norwegian girls, ages 6 to 16 years. MAIN OUTCOME MEASURES: Clinical and ultrasound breast evaluations were performed for all included girls. Blood samples were analyzed by immunoassay and ultrasensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantify estradiol (E2) and estrone (E1) from the subpicomolar range. RESULTS: References for E2, E1, luteinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin were constructed in relation to chronological age, Tanner stages, and US breast stages. An endocrine profile index score derived from principal component analysis of these analytes was a better marker of puberty onset than age or any individual hormone, with receiver-operating characteristic area under the curve 0.91 (P < 0.001). Ultrasound detection of nonpalpable glandular tissue in 14 out of 264 (5.3%) girls with clinically prepubertal presentation was associated with significantly higher median serum levels of E2 (12.5 vs 4.9 pmol/L; P < 0.05) and a distinct endocrine profile (arbitrary units; P < 0.001). CONCLUSIONS: We provide the first hormone references for use with US breast staging and demonstrate the application of endocrine profiling to improve detection of female puberty onset.

References for Ultrasound Staging of Breast Maturation, Tanner Breast Staging, Pubic Hair, and Menarche in Norwegian Girls.

CONTEXT: Discriminating adipose and glandular tissue is challenging when clinically assessing breast development. Ultrasound facilitates staging of pubertal breast maturation (US B), but has not been systematically compared to Tanner breast (Tanner B) staging, and no normative data have been reported. OBJECTIVE: To present normative references for US B along with references for Tanner B, pubic hair (PH), and menarche. DESIGN, SETTING, AND PARTICIPANTS: A cross-sectional sample of 703 healthy girls aged 6 to 16 years were examined. MAIN OUTCOME MEASURES: Breast development was determined with US B and Tanner B staging. Tanner PH and menarcheal status were recorded. The age distributions of entry in US B, Tanner B, and PH stages and menarche were estimated with generalized linear and generalized additive models with a probit link. Method agreement was tested with weighted Cohen's kappa. RESULTS: The median (±2SD) ages for thelarche, US B2 and Tanner B2, were 10.2 (7.7, 12.8) and 10.4 (8.0, 12.7) years. The median (±2SD) ages at Tanner PH2 and menarche were 10.9 (8.5, 13.3) and 12.7 (11.0, 16.2) years. Cohen's kappa of agreement (95% confidence interval) between US B and Tanner B was 0.87 (0.85-0.88). When the methods disagreed, US B was usually more advanced. CONCLUSION: Thelarche occurred at a slightly younger age when assessed with ultrasound compared to clinical Tanner staging, although the 2 methods had a very good agreement when determining pubertal breast maturation. A significant decrease of 2.8 months in age at menarche was observed during the past decade in Norwegian girls.

Reference data for testicular volume measured with ultrasound and pubic hair in Norwegian boys are comparable with Northern European populations.

AIM: To estimate references for testicular volume measured with ultrasound and Tanner stages of pubic hair in Norwegian boys, and to compare the timing of puberty with data from similar populations. METHODS: Testicular volume was derived from ultrasound measurements of testicular volume in a cross-sectional study of 514 healthy boys. A continuous testicular volume for age reference curve was estimated with the LMS method. Tanner stages for pubic hair were clinically assessed in 452 boys. Age references for pubertal milestones were estimated with probit regression. RESULTS: Puberty onset, defined by an ultrasound testicular volume of 2.7 mL, equivalent to an orchidometer volume of 4 mL, occurred at a mean (SD) age of 11.7 (1.1) years. The reference range was 9.7 (3rd) to 13.7 years (97th percentile). Pubic hair (Tanner stage 2) appeared on average at 11.8 (1.2) years with a corresponding reference range of 9.5-14.1 years. CONCLUSION: The references for testicular volume measured with ultrasound are continuous in age and allow for the quantification of pubertal development. The age distribution of reaching pubertal milestones was comparable with data from other Northern European countries.

Ultrasound-based measurements of testicular volume in 6- to 16-year-old boys - intra- and interobserver agreement and comparison with Prader orchidometry.

BACKGROUND: Prader orchidometry has been the standard method for evaluating testicular size. As this technique is subjective and tends to overestimate the testicular volume, ultrasound (US) has been proposed as more reliable. OBJECTIVE: To evaluate the intra- and interobserver agreement of US measurements of testicular volume and to compare US with the Prader orchidometer. MATERIALS AND METHODS: Dimensions of the right testicle were measured using US in 57 boys ages 6.5 to 16.4 years (mean: 12.0 years). The measurements were performed twice by one main observer and once by a second observer. A third observer estimated testicular volume using a Prader orchidometer. Agreement was investigated with Bland-Altman plots, summarized as the mean and standard deviation (SD) of differences, 95% limits of agreement and technical error of measurement. RESULTS: Mean intra-observer difference of testicular volume was 2.2%, SD=9.2% (limits of agreement: -20.3 to 15.9%) and technical error of measurement 6.5%. The mean interobserver difference was 4.8%, SD=20.7% (limits of agreement: -35.7 to 45.3%) and technical error of measurement 14.6%. Comparing US and orchidometer volumes required conversion that was nonlinear and volume dependent, estimated as VolOM = 1.96×VolUS0.71. The mean difference after transformation was 0.7% with an SD of 18.0% (limits of agreement: -34.5 to 35.9%). CONCLUSION: Our results showed a small mean intra- and interobserver difference that indicates the potential of US for measurement of testicular volume at group level. The intra-observer error was limited, which justifies its use in longitudinal follow-up of testicular development in an individual child, but the larger interobserver variability indicates the need for good standardization of methods. Agreement between the two methods requires a power transformation.

Ultrasound assessment of pubertal breast development in girls: intra- and interobserver agreement.

BACKGROUND: Clinical assessment of pubertal breast development using Tanner staging is subjective. This has led to the introduction of ultrasound (US), aiming for a more objective analysis. However, information regarding its reliability is lacking. OBJECTIVE: To examine intra- and interobserver agreement of breast maturity staging using US and to examine the precision of direct measurements of the gland. MATERIALS AND METHODS: Fifty-seven healthy girls (mean age: 10.9 years, range: 6.1 to 15.9 years) were examined independently by two observers using US of the left breast to score the glandular maturity stage on a 0-5 scale, and to measure the depth and diameter. One observer repeated the examination after 20 to 35 min to assess intra-observer agreement. Cohen's kappa with linear weights was used to examine intra- and interobserver agreement of the US staging, while the measurement precision was analyzed using Bland-Altman plots and 95% limits of agreement. RESULTS: The agreement of US staging on a 0-5 scale was very good (kappa 0.84; 95% confidence interval [CI] 0.78-0.91) for intra-observer observation and good (kappa 0.71; 95% CI 0.62-0.80) for interobserver observation. Measurements of glandular depth and diameter were unbiased for a single observer, but the variances were large both within and between observers. CONCLUSION: US using a scale from 0 to 5 is a reliable method to stage the development of glandular breast tissue during puberty in healthy girls. Measurements of glandular depth and diameter were found to be imprecise.