STUDY QUESTION Is there a difference in testicular function in early adulthood between men born with cryptorchidism and men born with normally descended testes?

SUMMARY ANSWER In men from the general population, a history of cryptorchidism was associated with lower total testis volume and impaired semen quality as well as altered serum levels of reproductive hormones.

WHAT IS KNOWN ALREADY The association between cryptorchidism and testicular function is well documented in studies based on sub-fertile or infertile men recruited from a clinical setting. However, the association has not previously been investigated in men from the general population, who were unselected regarding fertility status.

STUDY DESIGN, SIZE, DURATION This is a cross-sectional population-based study of 6376 young Danish men examined from 1996 to 2017.

PARTICIPANTS/MATERIALS, SETTING, METHODS This study is based on young men from the greater Copenhagen area, Denmark (median age of 19 years) who were unselected regarding fertility status and semen quality. The young men delivered a semen sample, had a blood sample drawn and underwent a physical examination including assessment of testis volume. Participants completed a questionnaire regarding cryptorchidism at birth, current lifestyle and their mother's pregnancy, after consulting their mother. The differences in markers of testicular function, including testis volume, semen parameters and reproductive hormones between men with and without a history of cryptorchidism were investigated with multiple linear regression analyses.

MAIN RESULTS AND THE ROLE OF CHANCE The participation rate was 24% for the entire study period. Overall, a history of cryptorchidism was associated with reduced testicular function. In the adjusted models, a history of cryptorchidism was associated with a 3.5 ml lower total testis volume, determined by orchidometer (P

LIMITATIONS, REASONS FOR CAUTION Information on cryptorchidism at birth and treatment modus was obtained by retrospective self-report, and each participant only delivered one semen sample.

WIDER IMPLICATIONS OF THE FINDINGS The results suggest that men with a history of cryptorchidism could be at increased risk of experiencing fertility problems. However, among these men there is a wide variation in semen quality and further research is needed in order to identify the subgroup of boys born with cryptorchidism who are at the greatest risk of impaired semen quality when reaching adulthood.