The body advances, as a rule, with the back toward the front of the mother. The shoulders with arms folded move under the pubic arch and then the head delivers in a state of flexion. The head, of course, has no caput and it is not moulded.
This mechanism may be greatly impeded or complicated at any stage of the movement. The advance may be retarded to a pathological degree, the belly may be large and as it passes along the canal one or both arms may be stripped up alongside the head or even into the back of the neck. The head may be arrested at the inlet by the arms, by its degree of deflexion, or by pelvic contraction.
The rotation may not take place, or it may be abnormal, and the belly of the child look forward toward the mother’s. Any of these variations adds further to the difficulty of the labor and to the danger of the partners in the event.
Artificial aid may be required which brings with it the possibility of sepsis.
The fœtal mortality which averages five per cent is due mostly to asphyxiation. Interference with the supply of oxygen begins as soon as the cord passes the vulva and the child must be delivered in eight minutes from that time, or perish. Partial detachment of the placenta may also cut off the oxygen to a fatal degree, and the child may be unable to breathe when born on account of mucus sucked into the trachea by premature efforts at respiration.
Minor accidents also occur, such as fractures, dislocations, and paralysis from injury to the nerve trunks.
Management.—In the interest of the child, this presentation is occasionally converted into a vertex by external version during the last weeks of pregnancy or in labor before the membranes have ruptured. It is difficult, however, to maintain the vertex over the inlet. The woman must be kept quiet in a horizontal posture and long roller splints applied to the side of the child in utero and bound on.
In primiparas, this is nearly impossible, and it is wiser, in the absence of some great necessity to warn the parents of the conditions and dangers and let them share in the responsibility.
Fig. 63.—Extraction of the breech. Traction on one leg. (Hammerschlag.)