Who is affected by undescended testicles

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

Citations

1. Schneck FX, Bellinger MF (2007). Abnormalities of the testes and scrotum and their surgical management. In AJ Wein, ed., Campbell-Walsh Urology, 9th ed., vol. 4, pp. 3761–3798. Philadelphia: Saunders Elsevier.
2. Elder JS (2007). Disorders and anomalies of the scrotal contents. In RM Kliegman et al., eds., Nelson Textbook of Pediatrics, 18th ed., pp. 2260–2265. Philadelphia: Saunders Elsevier.
3. Wenzler DL, et al. (2004). What is the rate of spontaneous testicular descent in infants with cryptorchidism? Journal of Urology, 171(2, Part 1): 849–851.