The epidemiology of cryptorchidism. John Radcliffe Hospital Cryptorchidism Research Group.

A total of 3,559 boys were examined for cryptorchidism over a 2-year period. At birth, 5.9% (210/3,534) had one or both testes undescended and at 3 months of age 1.61% (57/3,534) still had an undescended testis. These figures represent an increase in undescended testis of 40% at birth and 68% at 3 months when compared with figures collected in a similar study in the late 1950s. This increase in cryptorchidism still does not account for the increased number of orchiopexies being performed. Low birthweight was also found to be a risk factor for the presence of an undescended testis.