A: Nina, it sounds like your baby has what’s known as an umbilical hernia, an out-pouching of the abdominal tissues where the umbilical cord entered her body during the pregnancy. Umbilical hernias are very common, affecting about 10 percent of babies. Girls, African-American babies and premature babies are more likely to have them.

The umbilical cord comes through the umbilical ring, a ½-inch opening between the muscles on the right and left sides of the abdominal wall. After a baby is born, the umbilical cord is cut and the stump falls off, and the umbilical ring usually closes to make an “innie” belly button. But in your baby’s case, the umbilical ring hasn’t yet completely closed, and the tissues underneath can pouch out as a “hernia.”

You might have noticed that your baby’s umbilical hernia gets bigger when she cries or strains to have a bowel movement. This is due to increased pressure inside the abdomen, which can push the tissues outward through the hole. But when your baby is relaxed, you can gently push the tissues back in.

An umbilical hernia is different from an inguinal hernia, which is a hernia in the groin area that’s most common in older men. It’s a hernia in a different location, but it’s the same principle: the weak place between the muscles gets pushed open when there’s straining. The baby’s weak place is the belly button while an adult’s is more likely to be the groin.

You can be reassured that umbilical hernias usually don’t cause any problems. They don’t cause pain for the baby and usually go away on their own within 12 to18 months as the baby’s abdominal muscles grow and become stronger.

Although many cultures around the world have traditions of placing a coin over the hernia or a strap around the baby’s belly to try to reduce the hernia, this has not been shown to be effective. In addition, a coin can cause an irritation or allergy on the baby’s skin and could be a choking hazard if it got loose.

In all, approximately 85 percent of hernias close by 1 year of age. The smaller the opening, the more likely it is to close earlier. But some larger hernias can still close on their own by 4 to 5 years of age. Surgery is generally recommended in two instances: if the umbilical hernia is still present at 4 to 5 years of age, after which it’s unlikely to resolve on its own, or in the rare event that it becomes “strangulated,” meaning the pouched-out tissues get stuck and can’t be pushed back in. The surgery is considered relatively simple and safe, usually involving only a small incision and a couple of stitches.

Be sure to have your doctor continue to check and measure your baby’s umbilical hernia at her well-baby visits over the next year to see whether it’s resolving on its own, which is most likely, or whether surgery might be recommended later.