Among these factors, physical variables that affect the structure of the testes are particularly important. The descent usually is complete at birth or by the end of the first year of life. Researchers believe that the increased temperature within the abdomen harms the enzymes and proteins that are responsible for normal sperm production. Sperm quality may be especially poor in men who have bilateral undescended testes.
Cryptorchidism is a common childhood disorder.
These figures are evidence of the late occurrence of testes descent during fetal growth within the womb. Yet incomplete testicular descent is not just a physical abnormality. Fertility appears to improve among men who receive therapy for cryptorchidism before puberty. Most cryptorchidism cases have no known cause. Yet most experts recommend some form of therapeutic management between the child's first and second birthdays.