In boys, the testicles (testes) begin their development in the tummy (abdomen). Whilst your baby is growing and developing in your womb (uterus), the testicles gradually travel down into the testicles' sac (scrotum). This usually happens towards the end of your pregnancy. At birth, most boys have two testicles in the scrotum. However, in some babies, one or both of the testicles cannot be felt in the scrotum. The testicle will then be undescended. This is also known as cryptorchidism. The testicle is usually stuck in the canal that leads from the abdomen to the scrotum (the inguinal canal) but sometimes it stays inside the abdomen.
This is a companion discussion topic for the original article at https://patient.info/pregnancy/newborn-baby-screening-tests/undescended-testicles-cryptorchidism