A: Maribel, your nephew had what's known as meconium aspiration. This is when a baby has a bowel movement when he's still inside the amniotic fluid in the uterus, and he breathes it in during the birth.

Meconium is a dark green tarry substance that is the baby's first bowel movement. It's formed from the baby's own hair, skin cells, blood and mucus that are sloughed off into the amniotic fluid. During the pregnancy, the baby swallows the amniotic fluid to clean it, and the waste builds up as meconium in the baby's intestines.

Most babies pass the first meconium stool in the first 12 hours after birth. After it passes, a baby's stool is softer and more watery based on the breast milk or formula he drinks. In about 10 to 20 percent of births, the baby passes a meconium stool before birth. It's more likely to happen the longer after the due date a baby is born. It's also more likely when the baby is stressed at the end of the pregnancy and during childbirth if there is a pregnancy complication and the baby is not getting enough oxygen.

Usually when babies are born in meconium-stained amniotic fluid, the doctor is able to suction out the baby's mouth and nose before he takes his first breath to prevent him from breathing it in. Rarely, it cannot be prevented and the baby breathes it in. This thick material can plug up his airways and cause respiratory distress or difficulty breathing.

For some babies this is only a minor problem, but others develop pneumonia and need to be in newborn intensive care on an IV and a mechanical ventilator. Most babies recover fully but some can have persistent breathing problems or developmental delay from the temporary lack of oxygen, and some babies die if their condition is severe.

Chances are that your nephew will be OK. It's important for your sister to stay close to her baby at the hospital and communicate daily with the nurses and doctors about his condition. If she can pump her breast milk, this will help keep her baby healthier when he starts feeding and gets out of the hospital. It's also important for you and other family members and friends to support your sister.