An
undescended testicle is the most common genital and
urinary system abnormality that occurs in newborn
boys. The condition is more common in male twins or boys who are born
prematurely, or who have a low birth weight.
About 4% of boys have an undescended testicle when they are born. In
full-term babies, the rate is about 3%, or 3 out of 100. In premature babies,
it is about 30%, or 30 out of 100.1
Most undescended testicles move into their normal position in the
scrotum without treatment, usually by the time the baby is 3 months old. A
testicle that has not descended by the time the baby is 6 months old probably
will not do so on its own.2, 3
This condition is passed down in some families (about 15 out of 100
cases).1