Stretched penile length and its associations with testosterone and infertility

Male infertility can be associated with secondary sexual characteristics, hypogonadism, and several findings in the examination of external genitalia. We sought to identify if stretched penile length (SPL) is associated with infertility or baseline testosterone.

We performed a retrospective review of all males age 18-59 presenting to a Men's health clinic from 2014 to 2017. SPL of patients with infertility were compared to patients with any other complaint. Patients with Peyronie's disease, prior penile surgery, prostatectomy, on testosterone replacement, clomiphene or β-hCG were excluded from our study. Baseline characteristics were compared between the two groups (infertile vs. other). Linear regression was used to assess the association between infertility and testosterone with SPL after adjusting for patient age, BMI, and race. Scatterplot was used for correlation between testosterone and SPL.

Six hundred and sixty-four men were included in our study (161 infertile, 503 other). The unadjusted mean SPL in the infertile group was 12.3 cm compared to 13.4 cm in the other group (P<0.001). The significance remained when adjusted for age, BMI, testosterone and race (12.4 vs. 13.3, P<0.001). Mean total testosterone in the infertile group was not significantly different than the other group (414 vs. 422, P=0.68). Infertile men were younger than the other group (33.2 vs. 42.1 years, P<0.001). BMI did not significantly differ (28.9 vs. 28.9 kg/m², P=0.57). There was a weak positive correlation between testosterone and penile size in both the infertile group (r=0.20, P=0.01) and the other group (r=0.24, P<0.001).

Though SPL differed amongst our groups, adult testosterone levels did not. If developmental levels of testosterone exposure accounted for some of the differences in SPL between our two groups, these variations did not persist into adulthood. It remains unknown if reduced length is a result of genetic or congenital factors associated with infertility. Further investigation is needed to better understand the association of shorter SPL with male infertility.