Fetal abnormalities are observed in 17% of pre-term breech deliveries and in 9% of term breech deliveries. Cord prolapse occurs in 7.5% of all breeches. This incidence varies with the type of breech: 0-2% with frank breech, 5-10% with complete breech, and 10-25% with footling breech. Cord prolapse occurs twice as often in women who have had previous pregnancy (or multiparas) (6%) than in the first time pregnancy ( or primigravidas ) (3%).
Nuchal arms, in which one or both arms are wrapped around the back of the neck, are present in 0-5% of vaginal breech deliveries and in 9% of breech extractions. Fetal head entrapment may result from an incompletely dilated cervix and head that lacks time to mould to the maternal pelvis. This occurs in 0-8.5% of vaginal breech deliveries.