Shoulder presentations are uncommon (about 0.5% of births)[1] since, usually, toward the end of gestation, either the head or the buttocks start to enter the upper part of the pelvis, anchoring the fetus in a longitudinal lie.

With the rupture of the membranes, there is an increased risk of a cord prolapse as the shoulder may not completely block the birth canal.

[3] During labor the shoulder will be wedged into the pelvis and the head lie in one iliac fossa, the breech in the other.

[1] The uterus continues to try to expel the impacted fetus and as its retraction ring rises, the musculature in the lower segments thins out leading eventually to a uterine rupture and the death of the mother.

[1] Prior to the arrival of C/S the fetus usually died during protracted labor and the mother's life was at risk as well due to infection, uterine rupture and bleeding.

Once the uterus had contracted around the baby tightly, destructive interventions were used to save the life of the mother.