Does Having One Undescended Testicle Affect Fertility?

Undescended testicles—medically termed cryptorchidism—affect approximately 3% of full-term male infants and up to 30% of preterm newborns. While many cases resolve spontaneously within the first six months of life, persistent unilateral or bilateral cryptorchidism requires clinical evaluation due to well-documented implications for fertility, testicular function, and long-term cancer risk.

When one testicle remains undescended while the other descends normally—a condition known as unilateral cryptorchidism—the affected testicle is typically smaller in volume and may exhibit impaired spermatogenesis. This asymmetry reflects underlying histological changes: germ cell depletion, reduced Sertoli and Leydig cell numbers, and altered testosterone synthesis. Importantly, even the seemingly normal, descended testicle often shows subtle functional deficits, including lower sperm concentration and motility compared with healthy controls.

Fertility outcomes depend heavily on timing and intervention. Early orchidopexy—ideally performed between 6 and 18 months of age—helps preserve germ cell reserves and improves the likelihood of future fertility. Delayed correction beyond age 2 years correlates with significantly diminished sperm counts and higher rates of azoospermia. Men with a history of unilateral cryptorchidism have an estimated 65–85% chance of natural conception, whereas those with bilateral involvement face markedly reduced fertility potential, with spontaneous conception rates dropping to 30–40%.

It is critical to recognize that testicular size discrepancy alone does not determine fertility capacity; rather, it serves as a clinical marker of underlying developmental disruption. Comprehensive assessment—including physical examination, hormonal profiling (e.g., inhibin B, FSH, testosterone), and, when indicated, semen analysis in adulthood—is essential for accurate prognostication and personalized counseling.