When babies are aligned in the uterus to come out buttocks first, as opposed to head first--the way most babies come out of the uterus--it is called a breech presentation. The head is the largest part of a full term baby's body. Therefore, delivery of the buttocks first may not adequately open up the birth canal enough for the head to pass through. The head may then get stuck in the birth canal, leaving the infant and mother in a precarious situation. Most babies with a breech presentation are delivered by cesarean section. On occasion the infant can be turned around so that he is lined up to come out head first.