Why three in every hundred baby boys arrive with a testicle still hidden
Testicles form high inside the abdomen, near the kidneys, and must travel down into the scrotum before birth. Sometimes the journey stalls. About 3 percent of full-term boys and nearly a third of premature ones are born with at least one testis undescended, which makes it the most common birth defect of the male genitals.
The medical name, cryptorchidism, is Greek for hidden testicle. Most cases resolve by themselves: roughly 80 percent of undescended testes drop within the first year, usually in the first three months, so the true rate settles near 1 percent. Around two thirds of uncomplicated cases affect one side, more often the right. In nine cases out of ten the testis can be felt in the groin canal; occasionally it sits deep in the abdomen, strays off course entirely into the thigh or the opposite side, or seems to be missing.
Usually no cause is found. Genetics, the mother's health and environmental influences may disturb the hormones that guide descent, and very premature babies can simply be born before it happens. Low birth weight is a known factor, and some researchers suspect chemicals that disrupt fetal hormones; the Mayo Clinic lists parental exposure to certain pesticides as a risk.
The condition matters later in life. It is linked to reduced fertility, a higher chance of twisting and hernias, and testicular cancer. One study found about 10 percent infertility among men with one affected side, against about 6 percent in men generally, rising to about 38 percent when both sides were involved. Cancer risk is several times higher than average, with the peak between the late teens and mid-forties, and seminoma is the commonest tumour. Even the normally placed testis of an affected man carries about a fifth more risk.
Surgeons can bring the testis down in infancy with an operation called orchiopexy. A 2007 study in the New England Journal of Medicine found cancer risk was markedly lower when this was done before puberty rather than after, and a testis in the scrotum is far easier to check than one inside the abdomen.
Source: Cryptorchidism
