Undescended Testicle

Hi

At my son's birth, and later at his five weeks checkup, we were told that he had both of his testicles.

At his five months checkup, it was determined, however, that he has probably only one testicle, and that he has retractile testicles. Yesterday we gave him a warm bath, as the testicles tend to hide when it is cold, however we could not feel them.

We have read some articles that if the baby's testicle has not descended descended on its own within the first year of life, it is most likely that he gets a surgery.

What do you know about retractile resticles and what can be done about it?