What causes an undescended testicle?

The exact causes of undescended testicles are not known. A combination of genetics, maternal health, and other environmental factors might disrupt the hormones, physical changes, and nerve activity that influence the development of the testicles. Factors that might increase the risk of an undescended testicle in a newborn include Low birth weight; premature birth; family history of undescended testicles or other problems of genital development; conditions of the fetus that can restrict growth, such as Down syndrome or an abdominal wall defect; alcohol use by the mother during pregnancy; cigarette smoking by the mother or exposure to second-hand smoke; parents’ exposure to some pesticides.