Pubertal development in Norwegian boys : Ultrasound assessment of testicular volume, hormonal references, and association with anthropometric measurements

Abstract

Background Puberty marks the transition from childhood to adulthood and is characterized by physiological and psychological changes leading to sexual maturity and reproductive function. Assessment of pubertal development in boys is challenging, due to the intimate and subjective nature of the examinations. Over the last decades, several studies have suggested a trend towards earlier puberty in boys, but data from Norway have been lacking. Up-to-date descriptive data allow to investigate secular trends and are required to define early or late puberty, both of which may impact on later health outcomes. The underlying mechanisms that influence the timing and progression of puberty are, particularly in boys, not fully elucidated. Overweight and obesity, as well as exposure to endocrine-disrupting chemicals, have been proposed as possible drivers for the trend towards earlier puberty. Aims The main aims of this study were to explore ultrasound as a reliable method for assessment of testicular volume and to establish references for the timing of pubertal development in Norwegian boys based on ultrasound-measured testicular volumes and the development of pubic hair. In addition, the study also aimed to establish references for serum levels of testosterone and other reproductive hormones in relation to ultrasound-derived testicular volumes and to examine the association between pubertal status and anthropometric measures in boys. Materials and methods This study is based on data from Bergen Growth Study 2 collected in 2016–2017. A total of 514 healthy boys aged 6–16 years were examined with ultrasound to measure the testicular volume, as well as clinically to assess for development of pubic hair according to the Tanner scale. In addition, anthropometric measurements, including height, weight, waist circumference, and subscapular skinfolds, as well as body composition, including body fat percentage, were recorded, and blood samples were collected for most of the participants. Results Results showed that ultrasound can be used to quantitate testicular volume in boys, without interference from surrounding scrotal tissue. The intra- and interobserver error was acceptable for clinical use. Prader orchidometry, compared to ultrasound, tended to overestimate smaller testicular volumes. Norwegian boys reached pubertal testicular volume at a mean (SD) age of 11.7 (1.1) years, and the onset of pubic hair development occurred, on average, at 11.8 (1.2) years. The study also found that testicular volume accounted for more variance in serum testosterone levels than chronological age, and that male pubertal hormone reference intervals benefited from stratification by testicular volume. Further, low body mass index (BMI) and small waist circumference for age, rather than high BMI and large waist circumference for age, influenced the timing of pubertal development. Boys with low BMI for age entered puberty approximately 8 months later than normal-weight or overweight boys. Conclusion This study demonstrates the usefulness and potential advantages of ultrasound as a method for evaluation of testicular volume in boys. Implementation of an ultrasound protocol has the added advantage of enabling more objective measurements on a continuous scale. In this study, the first references for clinical assessment of puberty in Norwegian boys were developed, which showed that Norwegian boys exhibited pubertal timing that is comparable with current Northern European references, and no apparent secular trend towards earlier puberty was observed over the last decades. Stratification of pubertal hormone references based on objective ultrasound assessments of testicular volume was shown to narrow the reference ranges and thus has the potential to increase the diagnostic value of traditional references based on chronological age. Finally, the study showed that low, but not high, BMI for age was associated with pubertal status, indicating that all weight classes should be taken into consideration when assessing sexual maturation in children and adolescents.