When babies take their first breaths at birth, bits of meconium can enter the airway. They can then be inhaled deep into the lungs. The meconium may stick to the air sacs (alveoli). This makes it hard for your baby to take in oxygen. It may also trap air in the baby's lungs. It may also make some of the natural substances in the lungs that help breathing. like surfactant, wash away or become inactive.
It can also cause an infection, such as pneumonia. Most babies generally get better within a few days. But severe cases of meconium aspiration may lead to death in a small number of babies.