title: Postnatal penile length and growth rate correlate to serum testosterone levels: a longitudinal study of 1962 normal boys.
abstract: 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.
authors.affiliation: University Department of Growth and Reproduction Section 5064, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Malene
authors.initials: M
authors.lastname: Boas
authors.forename: Kirsten A
authors.initials: KA
authors.lastname: Boisen
authors.forename: Helena E
authors.initials: HE
authors.lastname: Virtanen
authors.forename: Marko
authors.initials: M
authors.lastname: Kaleva
authors.forename: Anne-Maarit
authors.initials: AM
authors.lastname: Suomi
authors.forename: Ida M
authors.initials: IM
authors.lastname: Schmidt
authors.forename: Ida N
authors.initials: IN
authors.lastname: Damgaard
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Kai
authors.forename: Marla
authors.initials: M
authors.lastname: Chellakooty
authors.forename: Niels E
authors.initials: NE
authors.lastname: Skakkebaek
authors.forename: Jorma
authors.initials: J
authors.lastname: Toppari
authors.forename: Katharina M
authors.initials: KM
authors.lastname: Main
mesh_terms: 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*
chemical_list: D013739:Testosterone