We don't really know why a few babies stay in a breech position. In some cases there is a physical reason that prevents them from turning head down. These can include:
Being premature
Small baby
Placenta previa
Less amniotic fluid
Twins or more
Bicornuate uterus
Low fibroids
Shape of the woman's pelvis
Baby with an abnormality
Emotional issues
Premature baby. Babies born before 34 weeks have a higher chance of being in a breech position, because they move freely and change position frequently, up until the last 6 to 10 weeks of pregnancy.
Small baby. For some reason, babies who are
small for gestational age (SGA) are more likely to be in a breech position. They can also have less amniotic fluid, which can contribute to them staying in this position.
Placenta previa. If the placenta is lying low in the uterus it can discourage the baby from assuming a head down position. This can be seen with an ultrasound after about 34 weeks of pregnancy. You can read more in
placenta previa.
Less amniotic fluid. If there is less than a normal amount of amniotic fluid surrounding the baby, called oligohydramnios, the baby is more restricted in their movement and less likely to move head down in the later weeks of their pregnancy.
Twins or more. Having more than one baby can mean that one (or both) stay in a breech position, as they move to accommodate each other. About 40% of twin pregnancies have at least one baby in a breech position (usually the second twin), who may turn head down once the first twin is born, or may stay breech (or move into a
transverse position). Sometimes the caregiver needs to manipulate the baby into position to be born. You can read more in
twins or more - giving birth.
Bicornuate uterus. A
bicornuate uterus is where the woman has a piece of tissue (septum) inside the uterus that extends from the top of her uterus (or fundus), not unlike a stalactite descending from the roof of a cave.