ESPE Abstracts

Background: In minipuberty, the male hypothalamic-pituitary-gonadal (HPG) axis is transiently activated triggering a surge in reproductive hormones causing growth of the genitalia. Longitudinal individual growth of the infant penis during minipuberty and associations to the HPG axis and IGF-I have not been thoroughly assessed.

Aim: To describe the development of penile length and width as well as their relation to serum concentrations of testosterone and IGF-I during minipuberty of healthy boys.

Methods: In total, 136 boys participated in the postnatal follow up in the longitudinal, prospective The COPENHAGEN Minipuberty Study (ClinicalTrials.gov ID: NCT02784184), where stretched penile length (SPL) and penile width (PW) were measured in 118 boys. All boys were examined up to six times during the first year of life including serum sampling. In total the 118 boys underwent n=606 clinical examinations. Testosterone was measured by liquid chromatography-tandem mass spectrometry (LC/MS-MS), IGF-I was measured using chemiluminescence immunoassay. Wilcoxon signed rank test was used to assess the development of penis size throughout minipuberty. Spearman’s rank correlation coefficient (r) was used to assess the correlation of penile width and length in relation to hormone levels.

Results: SPL increased significantly from 0 to 2.5 months of age (median (IQR) 32 (29-36) mm to 35 (31-38) mm, P=0.01), followed by a period up to 6 months of age, where SPL declined to 33 (29-36) mm, P<0.01. Hereafter, a more stable length was maintained until 1 year of age. PW increased more clearly from 0 to approximately 6 months of age; median (IQR) 11.2 (10.5-12.3) mm to 13.3 (12.1-14.2) mm, P<0.01, followed by more stable levels until 1 year of age, 12.9 (12.0-13.9) mm, P=0.54. The SPL/body weight ratio was positively correlated with circulating levels of testosterone and IGF-I; r= 0.7 and 0.6, respectively, both P<0.01. Likewise, the PW/body weight ratio was positively correlated with testosterone and IGF-I, r= 0.8 and 0.7, respectively, both P<0.01.

Conclusion: In this longitudinal study of healthy infant boys, penile width increased more clearly than penile length during minipuberty. Both penile length and width were positively correlated with circulating levels of testosterone as well as IGF-I. We speculate that penile width rather than penile length may be a valuable tool as predictor of hypogonadism in boys with micropenis.