My youngest had it. I was really worried, but the doc told us that it was fine and not to worry. That they only really worry if it is in the groin because it can cut off part of the bowel and it can become a big problem. But an umbilical hernia is nothing to worry about and that it usually clears up on it's own when the kids start moving around and using their abdominal muscles.
He said that it is caused because the abdomen muscles are in bands that go from the chest down to the groin and that when babies get the umbilical hernia that the muscles aren't tight between the bands and it can cause the intestines to poke though, because it is a weak spot.
My son's cleared up at about 6 months, but some babies need surgery after 12 months for it.
Good luck. I would just push it in when i noticed it poking through.
at 8:27 PM on Aug. 2, 2009