In the beginning of labor the shoulders are turned so as to correspond to the oblique diameter of the pelvic cavity, but they pass through the pelvis in a transverse position. After they reach the inferior strait, the body rotates so that the right shoulder of the child turns towards the left side of the mother and the wide diameter of the shoulders is accommodated to the wide diameter of the strait, and the rotation of the head, which is free externally, is secondary to the rotation of the shoulders.
In the EXPULSION OF THE BODY the right shoulder, or subpubic one, is the first one to appear in the vulvar fissure, but the left or posterior one may be disengaged at the commissure of the perineum before the right one is delivered; the remainder of the trunk is expelled very soon, describing a prolonged spiral course in its passage.
A child originally in the RIGHT POSTERIOR-ILIAC position becomes converted towards the last of the labor into an occipito pubic or anterior one, and the labor terminates as it does in A 1, when the occiput was originally in front. It is the left shoulder, however, which gets behind the arch of the pubis, and the occiput is directed towards the right thigh after the head emerges.
In some instances, though rarely, the child originally in A 4 position remains with the occiput behind to the termination of the labor. In such cases the forehead comes under the pubis and remains there for a time, while the occiput traverses the whole circle of the perineum; then the whole head and face is immediately delivered.
It is not deemed necessary to describe here the mechanism of labor in the more unusual varieties which are so very numerous.
As regards PROGNOSIS, head presentations are the most favorable of all, and those in which the occiput looks anteriorly in the beginning of labor are more favorable than those in which it is turned posteriorly. In occipito-posterior positions the labor is more tedious than when the occiput is in front, and the expulsion becomes particularly difficult when the head maintains its original position and does not rotate or take the pivot turn.
Upon the fœtal head after it is delivered there is almost always a protuberance to be found—a tumefaction, more or less considerable upon some point of the vertex; its greater size indicating a longer continuance of the labor, and its seat indicating in what position the child was born. This tumor is almost always located on one of the posterior superior angles of the parietal bones, and shows that the occiput escaped under the pubic arch. During the labor the whole head is strongly compressed except at one point on the vertex, which therefore becomes the seat of a sero-sanguinolent infiltration. This tumor disappears usually within forty-eight hours; if it does not, it may properly be punctured. It may contain either serum, or serum and blood, or grumous blood.
CHAPTER V.
DIAGNOSIS OF ARTIFICIAL LABOR.
When the expulsion of the fœtus takes place from the efforts of nature alone, the labor is called by some authors spontaneous or natural, but when art is obliged to interfere it is called artificial. It would be very useful to us if we could always decide in the commencement of labor whether the assistance of art would be required, and I will group together in a few pages such instructions as I am able to give on this important subject.
The nurse or midwife will not very generally be able to decide any point by auscultation, but she as well as the physician may judge from the appearance of the woman, from her past history, from palpation of the abdomen, and from vaginal touch. She should accustom herself to judging by all these means, that she may be able to decide early whether the help of an accoucheur will be imperatively needed.