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Running down the numbers on sexual maturity ratings

Also the author states that a male grows about one fourth of his adult height during puberty, a value that is reported three sentences later to be 11 inches-giving a final adult height approximately 44 inches.

Jon Matthew Farber, MDAlexandria, Va.

Author's reply Dr. Farber's first question regards average testicular volume. Findings from the most frequently cited study¹ of testicular volume during adolescence are reported in Table 1 of my article (at the request of the editors, two original tables-testicular volume by age and pubic hair stages-were combined). This study¹ is one of the few to describe testicular volume during adolescence, and is based on a cross-sectional Swiss sample of boys and young soldiers collected before 1974.¹ In their table, the authors separated SMR 5 and 6, which are typically collapsed in more current descriptions of sexual maturity ratings as SMR 5, representing "adult/mature." Also, this study did not include a sample of adult males. In my article, standard testicular volumes are described in the text and are adapted from Neinstein² and standard adolescent medicine training.

The next two matters regard the timing and sequence of puberty. The sequence of puberty is predictable: activation of the gonanotropic axis, production of testosterone, enlargement of testes, development of pubic hair, enlargement of the phallus, height spurt, etc...The timing of these events in a growing boy is, however, variable. Studies that have examined pubertal timing report both the median age of entry into different pubertal "events"³ and the mean age of the timing for these events. Sun and colleagues, for example, report both events. The median age of entry is described into SMR 2. For the text that follows, mean ages in years are described.

Last, the average normal growth velocities before puberty include the above table, described by Neinstein².

Also as described by Neinstein, "Height velocity increases again during puberty and peaks during the adolescent growth spurt. The mean year for beginning an increase in growth velocity is 11 in boys... Peak height velocity occurs at a mean of 13.5 years in boys... The magnitude of the growth spurt is negatively correlated with the age at which it begins, but there is no correlation with final height." Additional relevant text appears on pages 10 and 11 of Neinstein's textbook.

Arik V. Marcell, MD, MPHBaltimore, Md.

REFERENCES

1. Zachman M, Prader A, Kind HP, et al: Testicular volume during adolescence. Cross-sectional and longitudinal studies. Helv Paediatr Acta 1974;29:61