Aetiology
Aetiology is largely unknown. Factors that predispose pregnancies to breech presentation include preterm delivery, small for gestational age fetus, primiparity, congenital anomalies in the fetus, abnormal amniotic fluid volume, placental and uterine anomalies, and previous breech delivery.[5][6][7][8][9] All these factors are associated with increased infant morbidity and mortality.
Pathophysiology
Fetal and uterine size can influence breech presentation. Preterm infants are more likely to change their in utero position due to the smaller size. Larger fetuses may be forced into a cephalic presentation in late pregnancy due to space or alignment constraints within the uterus. Primiparity, female sex of baby, fetal congenital anomalies, and multiple pregnancies may all be indirectly related through association with small for gestational age. Parity-related relaxation of the uterine wall may reduce breech presentation by contributing to a higher spontaneous version and external cephalic version rate in multiparous women.[10]
Classification
Types of breech presentation[1][2]
Frank breech
Baby's buttocks lead the way into the birth canal
Hips are flexed, knees are extended, and the feet are in close proximity to the head
65% to 70% of breech babies are in this position.
Complete breech
Baby presents with buttocks first
Both the hips and the knees are flexed; the baby may be sitting cross-legged.
Incomplete or footling breech
One or both of the baby's feet lie below the breech so that the foot or knee is lowermost in the birth canal
This is rare at term but relatively common with premature fetuses.
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