CHAPTER XI
SYMPTOMS, COURSE AND MECHANISM OF NORMAL LABOR
Labor may be defined as the process by means of which the product of conception is separated and expelled from the mother’s body. It ordinarily occurs about 280 days from the beginning of the last menstrual period. (See p. 93.)
The cause of labor is not known. Many theories have been advanced to explain why the uterine contractions, which have occurred painlessly throughout pregnancy, and without expulsive force, finally become painful at the end of the tenth month and so changed in character as to extrude the uterine contents; but as yet, none is wholly satisfactory nor generally accepted. Nor is it known why some labors are premature and some delayed.
The onset of labor is usually marked by the patient’s becoming conscious of the uterine contractions through dragging pains which may be felt first in the back and then in the lower part of the abdomen and the thighs. At first the pains are feeble and infrequent, but they gradually grow more severe and more frequent. Intestinal colic is sometimes mistaken for labor pains, but when the paroxysms are rhythmical and the uterus is felt, through the abdominal wall, to grow hard as the pain increases and soft as it subsides, there can be no doubt but that the patient is in labor. The first signs of labor may be a gush of amniotic fluid, caused by the rupture of the membranes, or of blood, but these are not typical.
For purposes of convenience, labor is usually described as consisting of three periods or stages. The first stage begins with the onset of labor and lasts until the cervix is completely dilated; the second stage begins with the complete dilatation of the cervix and lasts until the child is born; the third stage begins with the birth of the child and lasts until the placenta is expelled.
The entire duration of labor may vary from a few moments, comprising a few pains, to several days of severe and exhausting pain, but the average length of the first labor is 18 hours and of subsequent labors about 12 hours, divided respectively into the three periods as follows:
_1st stage._ _2nd stage._ _3rd stage._ _Total._ Primipara 16 hours 1¾ hours 15 minutes 18 hours. Multipara 11 hours 45 minutes 15 minutes 12 hours.
The longer labor in primiparous women is due to the greater tone, and thus the greater resistance offered by the muscles of the cervix and perineum. Elderly primiparæ are likely to have longer labors than young primiparæ.
=First Stage.= This is frequently called the stage of dilatation. During this period the contractions of the uterine muscles make pressure upon the amniotic sac of fluid, forcing it gradually down and into the cervix as a water wedge, widening the internal os first, then the external os, until the entire canal is fully dilated (thinned out); shortened to about one-half inch in length and finally obliterated so that it is uninterruptedly continuous with the lower uterine segment. (Figs. 63, 64, 65, 66.)
The first stage pains begin by being mild and occurring at intervals of from 15 to 30 minutes, but they gradually increase in frequency and intensity until at the end of 14 to 16 hours they are very severe and recur every three or four minutes, each pain lasting about one minute. The pains begin in the back, pass slowly forward to the abdomen and down into the thighs.
The patient is entirely comfortable, as a rule, between pains and until they become very frequent will usually feel able, in fact prefer, to be up and about, but if she is on her feet when a contraction begins she will usually seek relief by assuming a characteristic leaning position (Fig. 67) or by sitting down, until the pain subsides. As dilatation advances, the patient has an increasing, sometimes persistent, desire to empty the bowels and bladder because of encroachment upon these two organs by the descending head. She may vomit, also, when the cervix becomes nearly or quite dilated.
FIGS. 63, 64, 65, AND 66 are diagrams showing stages of dilatation and obliteration of cervix during labor.
In the course of this stretching process, the cervix sustains many tiny lesions, from which blood oozes and tinges the vaginal discharge. This blood-stained secretion is often called the “show” and usually appears toward the end of the first stage.
As a rule, when the cervix is fully dilated the membranes rupture and there is a sudden gush of that part of the fluid which was below the fetus in the amniotic sac, but the rupture of the membranes does not necessarily mark the end of the first stage. In some instances they rupture before the cervix is fully dilated; in others, though not often, before the patient goes into labor, thus producing what is known as a “dry” labor.
The abdominal muscles do not contract very forcibly during the first stage, the expulsive force in this period coming almost entirely from the uterine contractions. The patient’s cries at this time are sharp and complaining in contrast to the groans and grunts which accompany the second stage.
Complete dilatation of the cervix marks the termination of the first stage.
=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.
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.
The long diameter of the head must first conform to one of the long diameters of the inlet, usually oblique, and then turn so that the length of the head is lying antero-posterior in conformity to the long diameter of the outlet through which it next passes. As the head descends and rotates it also describes an arc because the posterior wall of the pelvis, consisting of the sacrum and coccyx, is about three times as deep as the anterior wall formed by the symphysis. That part of the baby’s head which passes down the posterior wall of the pelvis must therefore travel three times as far in a given time as the part which simply slips under the short symphysis pubis.
In a vertex presentation, left-occipito-anterior position, while the occiput passes under the symphysis and appears at the distending vaginal outlet, the face passes down the posterior wall and along the floor of the pelvis. As pressure is exerted by the rapidly succeeding contractions, the head pivots about the pubis, thus extending the neck and pushing the face farther downward and forward. After emergence of the back and top of the head below the symphysis, the forehead appears over the posterior margin of the vagina, then the brow, eyes, nose, mouth and chin in turn, and the entire head is born. (Fig. 68.) The baby’s head then drops forward, in relation to its own body, with its face toward the mother’s rectum and the occiput in front of the pubis, but soon the occiput rotates toward the mother’s left side, resuming the relation that it bore to the inner aspect of her pelvis before expulsion. The undelivered shoulders are now antero-posterior, one under the pubis and the other resting on the perineum. (Fig. 69.) The lower, or posterior shoulder is born first (Fig. 70), followed quickly by the anterior shoulder and the rest of the body, and the amniotic fluid which was behind the child’s body. Thus is the second stage completed.
=Third Stage.= The third stage, sometimes termed the placental stage, is that period following the birth of the child, during which the placenta is delivered. For a few moments after the baby is born the tired mother lies quietly and free from pain, as there is a temporary cessation of the uterine contractions, and she often sleeps as a result of the anesthetic given during the second stage.
The uterus has greatly decreased in size, the fundus now lying below the umbilicus where it may be felt as a firm, solid mass. The uterine contractions are resumed in the course of a few moments and as they persist, the uterus grows smaller, thereby greatly decreasing the area of placental attachment. As the placenta is non-contractile it cannot accommodate itself to this decreased area of attachment, and so is literally squeezed from its moorings. It is then gradually forced down into the lower uterine segment where it may be located by the distension of the abdominal wall which it produces just above the symphysis. After the separation of the placenta is complete the uterus rises in the abdominal cavity until the fundus is felt above the umbilicus. The placenta, finally, may be completely expelled spontaneously, or expressed by slight pressure made upon the fundus by the accoucheur.
The placental detachment may begin at the centre, the area of separation spreading to the margin, or the detachment may start at the margin of the placenta and extend toward the centre. Either is normal. These two modes of placental separation are named the Schultze and the Duncan, respectively, from the men who first described them. (Fig. 71.)
In the Schultze mechanism, which occurs most frequently, the separating process begins at the centre of the placenta and the glistening fetal surface appears at the vaginal outlet. In this case there is practically no bleeding during the third stage as the inverted placenta blocks the vagina and holds back the blood.
In Duncan’s mechanism the detachment begins at the margin, the placenta rolls upon itself and presents at the outlet by its roughened maternal surface and there is usually slight but continuous bleeding from the time the separation begins. When the placenta is delivered, the collapsed membranes trail after it like a tapering cord. A good deal of blood is lost at the time of the placental expulsion and immediately afterwards, but this profuse bleeding usually subsides in a few moments. Although the loss of blood may be as much as 500 cubic centimetres without its being regarded as serious, the average amount is about 350 cubic centimetres.
The patient has been through a severe ordeal and at the end of the third stage of labor she is usually tired out and cold.