PART III.

LABOR.

CHAPTER I.

THE PHENOMENA OF LABOR.

Delivery at Term.-In considering delivery at term we have to discuss two distinct classes of events.

One of these is the series of vital actions brought into play in order to effect the expulsion of the child; and the other consists of the movements imparted to the child-the body to be expelled-in other words, the mechanism of delivery.

Causes of Labor.-Before proceeding to the consideration of these important topics, a few words may be said as to the determining causes of labor. This subject has been from the earliest times a quæstio vexata among physiologists; and many and various are the theories which have been broached to explain the curious fact that labor spontaneously commences, if not at a fixed epoch, at any rate approximately So. It must be admitted that even yet there is no explanation which can be implicitly accepted.

The explanations which have been given may be divided into two classes--those which attribute the advent of labor to the foetus, and those which refer it to some change connected with the maternal generative organs.

The former is the opinion which was held by the older accoucheurs, who assigned to the foetus some active influence in effecting its own expulsion. It need hardly be said that such fanciful views have no kind of physiological basis. Others have supposed that there might be some change in the placental circulation, or in the vascular system of the foetus, which might solve the mystery.

The majority of obstetricians, however, refer the advent of labor to purely maternal causes. Among the more favorite theories is one, which was originally started in this country [i. e., England] by Dr. Power, and adopted and illustrated by Depaul, Dubois, and other writers. It is based on the assumption that there is a sphincter action of the fibres of the cervix, analogous to that of the sphincters of the bladder and rectum, and that when the cervix is taken up into the general uterine cavity as pregnancy advances, the ovum presses upon it, irritates its nerves, and so sets up reflex action, which ends in the establishment of uterine contraction. This theory was founded on erroneous conceptions of the changes that occurred in the neck of the

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uterus; and, as it is certain that obliteration of the cervix does not really take place in the manner that Power believed when his theory was broached, it is obvious that its supposed result cannot follow. modification of this theory is that held by Stoltz and Bandl. According to this view, when the cervix softens during the last weeks of pregnancy, the painless uterine contractions of gestation act upon the os internum, and open it sufficiently to admit of the ovum pressing on the lower segment of the uterus, and so inducing labor.

Girin' contends that the descent and pressure of the foetal head on the os internum is favored by changes in the density of the liquor amnii. This attains its maximum density in the early months of pregnancy, when it is 1.030, and it diminishes steadily until term, when it is nearly that of water. The specific gravity of the foetus is at first lower than that of the amniotic fluid, but becomes steadily higher. Eventually the foetus, sinking on the os internum, excites the uterus to contraction.

This

Extreme distention of the uterus has been held to be the determining cause of labor, a view lately revived by Dr. King, of Washington, who believes that contractions are induced because the uterus ceases to augment in capacity, while its contents still continue to increase. hypothesis is sufficiently disproved by a number of clinical facts which show that the uterus may be subject to excessive and even rapid distention-as in cases of hydramnios, multiple pregnancy, and hydatidiform degeneration of the ovum-without the supervention of uterine

contractions.

Another inciter of uterine action has been supposed to be the separation of the ovum from its connection to the uterine parietes, in consequence of fatty degeneration of the decidua occurring at the end of pregnancy. The supposed result of this change, which undoubtedly occurs, is that the ovum becomes so detached from its organic adhesions as to be somewhat in the position of a foreign body, and thus incites the nerves so largely distributed over the interior of the uterus. This theory, which has been widely accepted, was originally started by Sir James Simpson, who pointed out that some of the most efficient means of inducing labor (such, for example, as the insertion of a gumelastic catheter between the ovum and the uterine walls) probably act in the same way, viz., by effecting separation of the membranes and detachment of the ovum.

Barnes instances, in opposition to this idea, the fact that ineffectual attempts at labor come on at the natural term of gestation in cases of extra-uterine pregnancy, when the foetus is altogether independent of the uterus, and, therefore, he argues, the cause cannot be situated in the uterus itself. A fair answer to this argument would be that although, in such cases, the womb does not contain the ovum, it does contain a decidua, the degeneration and separation of which might suffice to induce the abortive and partial attempts at labor then witnessed. Leopold' suggests that the advent of labor may be connected with

1 Arch. de Tocologie, No. 8, 1889.

2 American Journal of Obstetrics, 1870-71, vol. iii. p. 561

3Studien über die Schleimhaut," etc. Arch. f. Gyn., 1887, Bd. xi. s. 443.

other changes in the decidua which occur in advanced pregnancy. He points out that then giant cells, containing many nuclei, appear in the serotina which penetrate the uterine sinuses, and cause the formation in them of thrombi. The obstruction in the calibre of a number of these vessels leads to a stasis of the maternal blood returning from the placenta, and to an increase of carbonic acid in it, which may excite the motor centre for uterine contraction, which is known to exist in the medulla oblongata.

Objections to These Theories.-A serious objection to all these theories, which are based on the assumption that some local irritation brings on contraction, is the fact, which has not been generally appreciated, that uterine contractions are always present during pregnancy as a normal occurrence, and that they may be, and often are, readily intensified at any time, so as to result in premature delivery.

It is, indeed, most likely that, at or about the full term, the nervous supply of the uterus is so highly developed, and in so advanced a state of irritability, that it more readily responds to stimuli than at other times. If, by separation of the decidua, or in some other way, stimulation of the excitor nerves is then effected, more frequent and forcible contractions than usual may result, and, as they become stronger and more regular, terminate in labor. But, allowing this, it still remains quite unexplained why this should occur with such regularity at a definite time.

He

Tyler Smith tried, indeed, to prove that labor came on naturally at what would have been a menstrual epoch, the congestion attending the menstrual nisus acting as the exciter of uterine contraction. therefore refers the onset of labor to ovarian, rather than to uterine, causes. Although this view is upheld with all its author's great talent, there are several objections to it difficult to overcome. Thus, it assumes that the periodic changes in the ovary continue during pregnancy, of which there is no proof. Indeed, there is good reason to believe that ovulation is suspended during gestation, and with it, of course, the menstrual nisus. Besides, as has been well objected to by Cazeaux, even if this theory were admitted, it would still leave the mystery unsolved, for it would not explain why the menstrual nisus should act in this way at the tenth menstrual epoch, rather than at the ninth or eleventh.

In spite, then, of many theories at our disposal, it is to be feared that we must admit ourselves to be still in entire ignorance of the reason why labor should come on at a fixed epoch.

Mode in which the Expulsion of the Child is Effected.-The expulsion of the child is effected by the contractions of the muscular fibres of the uterus, aided by those of some of the abdominal muscles. These efforts are in the main entirely independent of volition. So far as regards the uterine contractions, this is absolutely true, for the mother has no power of originating, lessening, or increasing the action of the uterus. As regards the abdominal muscles, however, the mother is certainly able to bring them into action, and to increase their power by voluntary efforts; but, as labor advances, and as the head passes into the vagina and irritates the nerves supplying it, the abdominal

muscles are often stimulated to contract, through the influence of reflex action, independently of volition on the part of the mother.

There can be little doubt that the chief agent in the expulsion of the child is the contraction of the uterus itself. This opinion is almost unanimously held by accoucheurs, and the influence of the abdominal muscles is believed to be purely accessory Dr. Haughton,' however, maintains a view which is directly contrary to this. From an examination of the force of the uterine contractions, arrived at by measuring the amount of muscular fibre contained in the walls of the uterus, he arrives at the conclusion that the uterine contractions are chiefly influential in rupturing the membranes, and dilating the os uteri, bringing into action, if needful, a force equivalent to 54 pounds; but when this is effected, and the second stage of labor has commenced, he thinks the remainder of the labor is mainly completed by the contractions of the abdominal muscles, to which he attributes enormous powers, equivalent, if needful, to a pressure of 523.65 pounds on the area of the pelvic canal.

These views bear on a topic of primary consequence in the physiology of labor. They have been fully criticised by Duncan, who has devoted much experimental research to the study of the powers brought into action in the expulsion of the child. His conclusions are that, so far from the enormous force being employed that Haughton estimated, in the large majority of cases the effective force brought to bear on the child by the combined action of both the uterine and abdominal muscles is less than 50 pounds-that is, less than the force which Haughton attributed to the uterus alone. In extremely severe labors, when the resistance is excessive, he thinks that extra power may be employed, but he estimates the maximum as not above 80 pounds, including in this total the action of both the uterine and abdominal muscles. Joulin arrived at the conclusion that the uterine contractions were capable of resisting a maximum force of about one hundredweight. Both these estimates, it will be observed, are much under that of Haughton, which Duncan describes as representing "a strain to which the maternal machinery could not be subjected without instantaneous and utter destruction."

There are many facts in the history of parturition which make it certain that the chief factor in the expulsion of the child is the uterus. Among these may be mentioned occasional cases in which the action of the abdominal muscles is materially lessened, if not annulled—as in profound anæsthesia, and in some cases of paraplegia—in which, nevertheless, uterine contractions suffice to effect delivery. The most familiar example of its influence, however, and one that is a matter of everyday observation in practice, is when inertia of the uterus exists. In such cases no effort on the part of the mother, no amount of voluntary action that she can bring to bear on the child, has any appreciable influence on the progress of the labor, which remains in abeyance until the defective uterine action is re-established, or until artificial aid is given.

1 "On the Muscular Forces Employed in Parturition," etc. Dublin Quart. Journ. Med. Sc., 1870, vol. xlxi. p. 459.

Contraction of the uterus, then, being the main agent in delivery, it is important for us to appreciate its mode of action, and its effect on the ovum.

Uterine Contractions at the Commencement of Labor.-We have seen that intermittent and generally painless uterine contractions exist during pregnancy. As the period for delivery approaches, these become more frequent and intense, until labor actually commences, when they begin to be sufficiently developed to effect the opening up of the os uteri, with a view to the passage of the child. They are now accompanied by pain, which increases as labor advances, and is so characteristic that "pains" are universally used as a descriptive term for the contractions themselves. It does not necessarily follow that uterine contractions are painless until they commence to effect dilatation of the os uteri. On the contrary, during the last days or even weeks of pregnancy, women constantly have irregular contractions, accompanied by severe suffering, which, however, pass off without producing any marked effect on the cervix. When labor has actually begun, if the hand is placed on the uterus, when a pain commences, the contraction of its muscular tissue is very apparent, and the whole organ is observed to become tense and hard, the rigidity increasing until the pain has reached its acme, the uterine walls then relaxing, and remaining soft until the next pain comes on. At the commencement of labor these pains are few, separated from each other by a considerable interval, and of short duration. In a perfectly typical labor the interval between the pains becomes shorter and shorter, while, at the same time, the duration of each pain is increased. At first they may occur only once in an hour or more, while eventually there may not be more than a few minutes' interval between them.

If, when the pains are fairly established, a vaginal examination be made, the os uteri may be found to be thinned and dilated in proportion to the progress of the labor. During the contraction the bag of membranes will be felt to bulge, to become tense from the downward pressure of the liquor amnii within it, and to protrude through the os if it be sufficiently open. The membranes, with the contained liquor amnii, thus form a fluid wedge, which has a most important influence in dilating the os uteri (see Frontispiece). This does not, however, form the sole mechanism by which the os uteri is dilated, for it is also acted upon by the contractions of the muscular fibres of the uterus, which tend to pull it open. It is probable that the muscular dilatation of the os is effected chiefly by the longitudinal fibres, which, as they shorten, act upon the os uteri, the part where there is least resistance.

Partly then by muscular contraction, partly by mechanical pressure, the cervical canal is dilated, and as it opens up it becomes thinner and thinner, until it is entirely taken up into the uterine cavity.

There is no longer any obstacle to the passage of the presenting part of the child into the cavity of the pelvis, and the force of the pains now generally effects the rupture of the membranes, and the escape of the liquor amnii. There is often observed, at this time, a temporary relaxation in the frequency of the pains, which had been steadily