Using the puberty reference data
An assessment of pubertal development is generally based on clinical examination of secondary sexual characteristics. In girls, the onset of puberty is defined by whether breast development has started. In boys, the onset of puberty is defined by whether the testicular volume has reached 4 mL, and this is assessed by comparative palpation of the testes using a Prader orchidometer (see appendix 1 for the clinical methods used to assess pubertal development).
The puberty reference data are based on the so-called Tanner scale, which was published by the paediatrician James Tanner in the 1960s (6, 7). The Tanner scale is used to define the stages of pubertal maturity, with quantity of pubic hair (in both sexes) and breast maturation (in girls) being measured on a scale from 1 to 5. Not all girls/women reach stage B5/P5, and not all boys reach P5, so these stages have been excluded from the reference data. The revised reference data also present new percentiles for first menstruation (menarche).
In the second Bergen Growth Study, ultrasound was used as an additional means of establishing pubertal development. This is a new method used to characterise the stages of breast maturation and testicular volume. Because ultrasound is not available in normal clinical practice, these measurements are not included in the updated reference data.
As before, reference data for pubic hair, breast development, menarche and testicular volume are shown as percentiles on horizontal lines along the x-axis of the growth curves (see appendices 2 and 3). The 3rd, 10th, 25th, 50th, 75th and 97th age percentiles are indicated with numbers. The 3rd percentile indicates the age at which 3 % of girls and boys respectively have reached a certain stage.