Breech Birth - Etiology

Etiology

Certain factors can encourage a breech presentation. Prematurity is likely the chief cause. Twenty five percent of fetuses are in the breech position at 32 weeks gestation; this drops to three percent at term. The increasing size of the fetus near term traps the fetus into the head down position normally. Pregnancies ending in preterm birth simply recruit more breeches before they can turn to head down. Factors predisposing to term breech presentation include:

• multiple (or multifetal) pregnancy (twins, triplets or more)
• abnormal volume of amniotic fluid: both polyhydramnios and oligohydramnios
• fetal anomalies: hydrocephaly, anencephaly and other congenital abnormalities
• uterine abnormalities
• prior Caesarean section
• contracted pelvis
• placenta praevia
• congenital malformation of the uterus such as septate or bicornuate uterus
• multiparae with lax abdominal wall

It is postulated that the baby normally assumes a head down presentation because of the weight of the baby's head. As the mass of the fetal head is the same as that of the pelvis, it is more likely that the enlarging fetus is more and more restricted in its movements, and simply becomes entrapped. The shape of the uterus is a more likely determinant of the final fetal presentation as uterine shape anomalies are strong predictors of breech presentation and other malpresentations.