Cryptorchidism is the most common birth defect involving male genitalia. It means one or both testicles haven’t descended into the scrotum. About 3% of full-term boys and 30% of premature boys are born with at least one undescended testicle, though the majority resolve on their own within the first few months of life.
How Testicles Normally Descend
During fetal development, the testicles form inside the abdomen near the kidneys. They gradually migrate downward, passing through the inguinal canal (a passage in the lower abdominal wall) and into the scrotum. This process is typically complete by the seventh month of pregnancy, which is why premature boys have such a high rate of undescended testicles: they were born before the process finished.
The descent is driven by hormones and a ligament called the gubernaculum, which essentially guides the testicle into position. When something disrupts this process, whether hormonal, structural, or genetic, the testicle can stall anywhere along the path or, in rarer cases, end up in an abnormal location entirely.
Known Risk Factors
Prematurity and low birth weight are the strongest predictors. Beyond that, research has identified several maternal and environmental factors. Smoking during pregnancy and gestational diabetes both increase the risk. There’s also growing evidence that certain environmental chemicals with hormone-disrupting properties can interfere with the signals that guide testicular descent, either by blocking the effects of male hormones or mimicking the effects of estrogen.
Family history plays a role as well. Having a father or brother with the condition raises a boy’s likelihood of being born with it.
What Happens in the First Year
Most undescended testicles come down on their own. Around 80% of cryptorchid testes descend within the first three months after birth, which brings the true prevalence down to roughly 1% of boys by age one. This is why pediatricians monitor the condition rather than intervening immediately.
The current guidelines from the American Urological Association are clear on the timeline: if a testicle hasn’t descended by six months of age (adjusted for prematurity), it’s unlikely to do so on its own. At that point, the child should be referred to a surgical specialist.
How It’s Diagnosed
Diagnosis is primarily hands-on. A doctor carefully examines the groin and scrotum to determine whether the testicle can be felt (palpable) or not (non-palpable). About 80% of undescended testicles are palpable, meaning the doctor can locate them somewhere along the inguinal canal. The remaining 20% can’t be felt on examination, which means the testicle could be sitting higher in the abdomen or may not have developed at all.
You might expect ultrasound to be a standard next step, but it’s actually not very useful here. A systematic review of the evidence found that ultrasound has only about 45% sensitivity for locating non-palpable testicles. It can’t reliably rule out an abdominal testicle, and its results don’t change what needs to happen next. For non-palpable cases, surgical exploration (typically using a small camera inserted through a tiny abdominal incision) is the definitive way to find the testicle, bring it down, or confirm it never developed.
Surgery and Timing
The standard treatment is a procedure called orchidopexy, where the testicle is moved into the scrotum and secured in place. For palpable testicles, this is typically a single operation through a small incision. For non-palpable or abdominal testicles, it may require a staged approach with a camera-assisted technique.
Timing matters significantly. Current guidelines recommend completing surgery by 18 months of age. Research comparing outcomes found that boys who had the procedure at nine months had better testicular growth than those who had it at three years. The earlier the testicle reaches the scrotum, the better its chances of developing normally.
Hormonal treatments have been tried historically, using injections that stimulate the body’s own testosterone production to encourage descent. However, success rates are low, and current guidelines focus on surgical correction as the standard of care.
Long-Term Fertility Effects
Whether cryptorchidism affects fertility later in life depends heavily on whether one or both sides were involved. Men who had a single undescended testicle generally have normal paternity rates and sperm counts comparable to the general population. About 17 to 30% may show somewhat lower sperm density, but this doesn’t necessarily prevent fatherhood.
Bilateral cryptorchidism (both testicles undescended) tells a different story. Roughly 50% of these men have decreased sperm density, and in untreated bilateral cases, the rate of producing no sperm at all reaches as high as 89%. In one follow-up study, only two out of 15 men with bilateral cryptorchidism were able to father children. Early surgical correction is specifically recommended to preserve whatever fertility potential exists.
Testicular Cancer Risk
Men with a history of cryptorchidism have a 5 to 10 times higher risk of testicular cancer compared to the general male population. About 10% of all testicular cancer cases occur in men who had an undescended testicle. The risk is higher when the testicle was located in the abdomen rather than the inguinal canal, and higher in the affected testicle itself compared to the one that descended normally (a relative risk of 6.33 versus 1.74).
Age at correction matters here too. Men who had surgery before age 13 had a cancer incidence rate of about 2.2%, compared to 5.4% for those treated after 13. Orchidopexy doesn’t eliminate the increased risk entirely, but earlier treatment is associated with lower rates. Just as importantly, bringing the testicle into the scrotum makes it possible to feel for lumps during self-examination, which is the primary way testicular cancer gets caught early.