The embryo develops early sex organs in the first several weeks after the egg is fertilized. If early testes do not develop in males before 8 weeks into the pregnancy, the baby will have female genitals.
If the testes disappear between 8 and 10 weeks, the baby will be born with ambiguous genitalia. This means the child will have parts of both male and female genitals.
However, if the testes disappear between 12 and 14 weeks, the baby will have normal male genitals (penis and scrotum), but no testes. This is known as congenital anorchia, or the "vanishing testes syndrome."
The cause is unknown. Genetic factors may be involved in some cases. .
This condition should not be confused with bilateral undescended testes, in which the testes are located in the abdomen or groin.