• The baby is not yet full term. If the mother goes into labor early, a baby may not have had the chance to settle into the cephalic presentation. More preterm babies than full-term babies are born breech.



• The mother has had a lot of babies. A relaxed, stretched-out abdominal wall allows a fetus to change position more freely, so once the baby aligns itself headfirst, it may not "stick" there like it would if it were held in place by a tighter abdomen.
  
  Also, in most first pregnancies, the baby is engaged into the pelvis by full term. But in women who have already had children, the baby may not engage until partway through labor (again, allowing the baby to change position more freely).



• Multiple fetuses. In twins, triplets, and larger sets of multiples, one of the babies will frequently be breech or transverse, because there often isn't enough room for all of them to line up headfirst. While the first baby's head may fit nicely into the mother's pelvis, keeping it headfirst, the subsequent ones don't have the bowl of the pelvis to fit into.



• Too much or too little amniotic fluid. When there is excess amniotic fluid, the baby's position may be unstable, allowing easier rotation from cephalic to breech and back. Conversely, very little amniotic fluid may hinder the baby's ability to rotate into the cephalic presentation.



• Obstruction to the baby assuming the headfirst position. If the placenta is down across the cervix, as in placenta previa, or if fibroid tumors are present down there, there may not be room for the baby's head to settle into the pelvis. Usually these conditions are readily diagnosed on ultrasound.
  
  Sometimes the uterus has an unusual shape or a dividing wall up the middle (septum) so that the baby may not be able to move into a cephalic presentation. This type of obstruction might not be recognized unless a C-section is done.



• The baby has a neurological problem. In a few cases of breech presentation, the baby doesn't move well enough to get into a headfirst position because of a neurological problem. One of the controversies about allowing breech vaginal delivery is that if the baby shows neurological problems after birth, it may be unclear if they were caused by a difficult vaginal breech delivery or if they predated the birth. For more on this subject, see Delivering a Breech Baby.



• Unknown factors. Much of the time, practitioners never find out why a baby was breech at full term. A percentage of healthy babies who showed no risk factors for breech are nonetheless in a feet- or butt-first position when it is time to be born.

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