Complete dilatation of the cervix marks the termination of the first stage.
Fig. 68.—Diagram indicating the rotation and pivoting of baby’s head during birth.
Second Stage. The second stage is sometimes called the stage of descent, or expulsion, of the fetus. The patient should and is usually quite willing to be in bed throughout the second stage, during which she should not be left alone. The pains are now regular, occurring at intervals of about two minutes from the beginning of one to the beginning of the pain following, and as the contractions last about one minute and are excruciatingly painful, the patient has very little respite from her suffering. Her face is flushed and she may perspire freely.
The abdominal and respiratory muscles are brought into active use during the second stage, contracting simultaneously with the uterine muscles and increasing their expulsive force. These are apparently controlled by the patient’s will at first, and she is able somewhat to increase their power by taking a deep breath, closing her lips, bracing her feet, pulling against something with her hands, straining with all her might and “bearing down.” Finally, however, the whole bearing down process becomes involuntary, is accompanied by intense pain and the deep grunting sound, which is characteristic of the well-advanced second stage. Under normal conditions, the child descends a little farther into the pelvis with each contraction, and finally the presenting part begins to distend the perineum and to separate the labia advancing at the height of each pain and slipping back a little as it subsides.
Fig. 69.—Anterior shoulder being slipped from under symphysis to facilitate birth of posterior shoulder.
The baby descends into and through the mother’s pelvis by means of a series of twisting and curving motions, accommodating the long axes of its head to the long diameters of the pelvis. The head being somewhat compressible and mouldable, because of imperfect ossification, is capable of a good deal of accommodation to the mother’s pelvis.
The mechanism of labor, therefore, is virtually a series of adaptations of the size, shape and mouldability of the baby’s head to the size and shape of the mother’s pelvis. If the head passes through the inlet satisfactorily, the rest of the labor will usually be accomplished with comparative safety. But a marked disproportion between the diameters of the head and pelvis may interfere with the engagement or descent of the head and produce a serious complication.
