During normal fetal development, the testicles form in the abdomen and gradually descend through the inguinal canal into the scrotum, usually finishing the journey during the third trimester. Cryptorchidism occurs when that descent is interrupted, leaving one or both testicles in the abdomen, inguinal canal, or upper scrotum at birth. The exact trigger varies from child to child and may involve hormonal signaling, anatomic factors, prematurity, low birth weight, or genetic influences.
According to the National Institute of Diabetes and Digestive and Kidney Diseases, premature birth is the strongest single risk factor, with up to 30 percent of preterm boys affected compared with about 3 percent of full-term infants. Family history of cryptorchidism, maternal exposure to certain chemicals, gestational diabetes, and low birth weight have also been associated with higher rates. In some children, no specific cause is ever identified, and that is normal. The condition is a developmental finding, not anything a parent did or could have prevented.
In older boys, a previously normal testis can occasionally retract upward and stop returning to the scrotum spontaneously, a pattern called an ascending or acquired undescended testis. This usually develops between ages 4 and 10 and is one reason routine well-child exams remain important throughout childhood.
