Postnatal penile length and growth rate correlate to serum testosterone levels: a longitudinal study of 1962 normal boys.
OBJECTIVE
Infant boys show a brief activation of their hypothalamic-pituitary-gonadal axis shortly after birth, the physiological significance of which is poorly understood. The objective of the study was to investigate the correlation between endogenous testosterone levels and penile size and growth.


METHODS
Prospective, longitudinal population-based study taking place at two large primary obstetric centres at the University Hospitals of Copenhagen, Denmark, and Turku, Finland.


METHODS
Infant boys, 728 Danish and 1234 Finnish, underwent clinical examinations at 0, 3, 18 and 36 months in Denmark and at 0, 3 and 18 months in Finland with blood samples taken at 3 months (n = 630). Penile length and growth were registered and reproductive hormones (testosterone, sex hormone binding globulin, oestradiol) were analysed.


RESULTS
Penile length increased from birth (3.49+/-0.4 cm) to 3 years of age (4.53+/-0.51 cm) with the highest growth velocity from birth to 3 months (1.0 mm/month). Penile length and growth were significantly, positively correlated to serum testosterone (r = 0.31 and 0.076, P = 0.006 and 0.001 respectively) and to free testosterone index (r = 0.385 and 0.094, P = 0.0001 and 0.0001 respectively).


CONCLUSIONS
We found that endogenous testosterone was significantly associated with penile size and growth rate in infant boys. Thus, the postnatal surge in reproductive hormones appears to be important for genital growth. Our data may serve as an updated reference for normal penile length in Caucasian boys up to 3 years of age.
Boas
Malene
M
University Department of Growth and Reproduction Section 5064, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
Boisen
Kirsten A
KA
Virtanen
Helena E
HE
Kaleva
Marko
M
Suomi
Anne-Maarit
AM
Schmidt
Ida M
IM
Damgaard
Ida N
IN
Kai
Claudia M
CM
Chellakooty
Marla
M
Skakkebaek
Niels E
NE
Toppari
Jorma
J
Main
Katharina M
KM
D000375:Aging; D002675:Child, Preschool; D003718:Denmark; D005387:Finland; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D010413:Penis / Q000033:anatomy & histology / Q000254:growth & development*; D012016:Reference Values; D013739:Testosterone / Q000097:blood*
D013739:Testosterone