About the growth studies

Updated knowledge of growth and weight development is important for all health-related work with children and adolescents, due to follow up of the child, but also to monitor trends in the child population.Children’s growth and development depends on heredity and environment. Norwegian children have gradually grown taller over the last hundred years, which reflects among other things, better well-being, improved nutrition and fewer infections. In the last 20-30 years weight in older children and adults has also increased.


The Bergen Growth Study 1:

The Bergen growth study 1 is a research project that was started in 2003 and which, among other things, aims to identify and describe the growth and weight development of Norwegian children. Data has been collected from more than 8000 children aged 0-19 years who where measured at the Health clinics, kindergartens and schools in Bergen in 2003-6. You can read more about the research project here.

Growth curves:

In the winter of 2007-2008 new growth curves was made for Norwegian children aged 0-19 years based on data from the growth study in Bergen and the Medical Birth Registry. Norwegian school children are taller today than the previous growth references show. Weight for height has also increased. You can read more about the curves and download them here.

The Bergen Growth Study 2:

The first childhood growth study (Vekststudien i Bergen 1) was conducted between the years 2003 and 2006, which made it possible to develop growth charts in use throughout the country since then. I the time period January-June 2016 data was collected to The Bergen Growth Study 2, a study focusing on pubertal developent in Norwegian children. Our knowledge of puberty in Norwegian children is limited. In other countries, such as Denmark and the United States, researchers are seeing indications that children reach puberty earlier than before. It is unclear why this is happening. Children may be reaching puberty earlier due to altered body composition (increased fat tissue) or because they are absorbing substances that influence this development (so-called endocrine disruptors). Early puberty has its downsides; it can increase the risk of obesity, have negative psycho-social implications and some studies have associated early puberty with certain forms of cancer. The purpose of our study is to document normal range of puberty among Norwegian children by measuring growth, mapping development, analyzing hormones in blood and saliva, and identify the genes that are involved. We wish to provide objective measurements of this development by taking into use ultrasound. Furthermore, we want to examine factors that may influence development by measuring body composition and the occurrence of endogenic disruptors in the body.

Height, weight and waist circumference was measured in all participants. All measurements were done at the child’s school. Furthermore, for the girls, a female nurse measured the size of the mammary glands by using ultrasound. For the boys, a male radiographer measured the size of the testicles, also by using ultrasound. The development of pubic hair was also registered. Body composition was also measured by using a method called bioimpedance. Bioimpedance equipment measures quantities of muscle, bone and fat in the body. Blood and saliva samples were taken thereafter. Parents were asked to fill out a questionnaire.

Two PhD-candiates and one postdoctor are now working on the data material. Summary of the first publications:

Pubertal development in boys:

Oehme N et al. Ultrasound-based measurements of testicular volume in 6- to 16-year-old boys — intra- and interobserver agreement and comparison with Prader orchidometry. Pediatr Radiol 2018.

Summary: The most common method of assessing testicular volume is by using a Prader orchidometer. In our study, we wanted instead to use ultrasound to get a better and more direct measurement of the testicular volume. We examined the repeatability and variation between ultrasound measurements done by one examiner measuring the testicular size twice, and between measurements of the same boy done by two different examiners. We did this on 57 boys. We found a relatively small average difference between the measurements made by the same examiner and between the measurements made by two different examiners. Our results show that ultrasound is a good examination method to use at a group level, while for use on the individual child, it is desirable that the same examiner measures the testicular volume at controls.

Oehme N et al. Reference data for testicular volume measured with ultrasound and pubic hair in Norwegian boys are comparable with Northern European populations. Acta Paediatr 2020.

Summary: The Bergen Growth Study 2 is the first study in Norway on pubertal development in Norwegian boys. We present puberty references based on data from 514 boys aged 6-16 years. The boys start puberty when at least one of the testicles reaches a volume of 2.7 ml measured by ultrasound. This happened at an average age of 11.7 years. Since the variation is large between individuals, normal pubertal onset for boys is defined to start between 9 and 14.5 years of age. We also investigated at what age pubic hair appeared, which was on average 11.8 years. Since there is no previous data on pubertal development in Norwegian boys, it is difficult to say whether they enter puberty earlier than before. However, when we compare our findings with studies from other countries such as Denmark and the Netherlands, we see that the Norwegian boys start their puberty at about the same age as them.

Madsen A et al. Testicular ultrasound to stratify hormone references in a cross-sectional Norwegian study of male puberty. Journal of Clinical Endocrinology and Metabolism (JCEM) 2019.

Summary: Testosterone is produced by maturing testicles during puberty, and serum level of testosterone is used as a biomarker of pubertal onset and development. In the current article, we present serum level of puberty-related hormones in relation to testicular volume measured by ultrasound. We show that testosterone levels are more correlated with testicular volume than with chronological age during puberty. This is the first article with sufficient statistical power to provide hormone references in relation to testicular volume, as opposed to traditional references based on age.

Endocrine references are important tools in pediatric medicine. With the blood samples from Bergen Growth Study 2, we have an unprecedented dataset to establish references that reflect the healthy pediatric population in Norway.

Pubertal development in girls:

Bruserud IS et al. Ultrasound assessment of pubertal breast development in girls: intra- and interobserver agreement. Pediatr Radiol 2018.

In this study, we introduce and test the intra- and interobserver agreement in using ultrasound as a method to categorize pubertal breast development on a scale from 0 to 5, in 6 to 16 year old girls. Direct measurements of the mammary gland were also done. A total of 57 girls were examined twice by one observer, and once by a second observer. The agreement, analyzed with Cohen’s kappa with linear weights, of ultrasound staging was very good for one observer (kappa 0.84; 95% confidence interval [CI] 0.78-0.91), and good between two observers (kappa 0.71; 95% CI 0.62-0.80). Measurements of glandular depth and diameter were found imprecise.

Bruserud IS et al. References for Ultrasound Staging of Breast Maturation, Tanner Breast Staging, Pubic Hair, and Menarche in Norwegian Girls. Journal of Clinical Endocrinology and Metabolism (JCEM) 2020.

With data from Bergen Growth study 2, we report the first pubertal references based on data from 6 to 16-year-old Norwegian girls.  The paper includes references for breast development (examined according to Tanner breast stages (n=700) and ultrasound breast stages (US B, n=696)), first menstruation (menarche (n=643)) and pubic hair development (Tanner PH stages (n=372)). The median age for Tanner B2 (onset of breast development) was 10.4 years, while the ultrasound determined onset of breast development was 10.2 years. Median age at menarche was 12.7 years, and for onset of pubic hair development, median age was 10.9 years. There are no previous Norwegian studies including estimated age at pubertal onset to compare with, but the ages at breast development in other North-European counties are comparable. Menarche occurred significantly earlier in Bergen Growth study 2 compared to Bergen Growth study 1, and the difference was also significant when accounting for body mass index. The new references for pubertal development may replace the current references that are based on a Danish study conducted in the 90-ties.