The pains are thus found to have three stages, one of inception or in crease, one of maximum intensity and one of diminution. The increasing stage may be very short, and the same is true of the stage of greatest in tensity, but the period of subsidence is relatively long. The whole pain lasts, generally, from sixty to eighty seconds. Feeble at first, the pains soon grow more severe, and, since they correspond to the cervical dilata tion, they are called preparatory. They become expulsory and very vio lent at the end of parturition.
Although the pains grow more and more painful as labor approaches its termination, the final ones are better tolerated than those which cor respond to the dilatation of the cervix. It is especially during the stage of dilatation that women manifest their sufferings by such cries and com plaints that we have heard this period designated by an experienced mid-wife as the period of despair. In favorable cases the pains begin in the loins, next invade the lateral abdominal regions, and terminate an teriorly—thus embracing the whole pelvic region. In other cases, the pain is persistently localized in the lumbar region. Generally it prevails in that region until the head passes through the cervix, then giving place to expulsive pains, which last until delivery is accomplished. With pre mature rupture of the membranes, high position of the foetus, rigidity of the cervix, deformities, or faulty presentations, the pains are often excruciating, and, unfortunately, intractable. Different explanations have been given to account for the pains, particularly for lumbar pains. Mattei attributes them to pressure of the uterus against the spinal column, and Beau to lumbo-abdominal neuralgia, analogous to that ac companying uterine affections. The causes of the pain vary, as Tarnier and Chantreuil remark, with the different stages of labor. Boivin is right in assuming that distension of the cervix is the chief agent in pro ducing pain, but we shall also include, among the causes of pain, disten sion of the perineum, of the vagina, and of the anus, besides compression of uterine and pelvic nerves and of pelvic organs.
The influence of contractions upon the foetus and the mother is ex tremely interesting. On auscultating the foetus, at the moment of a pain, one hears the foetal heart-beats grow slower and weaker as the con traction grows stronger, only to return to their normal condition when the pain subsides. In rare cases, the heart-sounds completely disappear. When this happens the interruption of the sounds is of very short dura tion, and corresponds to the maximum intensity of contraction. This
slowing of the foetal heart is attributed, by Schwartz, to an increase in intnt-cardiac pressure, by Schultze to slight asphyxia of the foetus, from placental compression, and by Kehrer to compression of the cranium and of the brain. The pains exert an accelerating influence upon the mater nal pulse. The acceleration is augmented as the pain progresses, and gradually disappears with the subsidence of the contraction. Hohl, who counted the pulse during a pain which lasted two minutes, gives the following figures: As labor progresses the pulse becomes more rapid, so that it is as frequent, just before the expulsion of the fcetus, in the interval of the pains, as it was at the height of the pain in the early stages of labor. The character of the uterine contractions, as above described, will suffice for their differentiation from so-called false pains, which originate in organs other than the uterus, and are due to a pathological condition of the womb. We shall have occasion to revert to this subject. The uterine contractility sometimes persists, for a time, after the death of the mother, and thus allows a living fcetus to be expelled.
2. Contraction of the Abdominal Muscles.
The contraction of these muscles does not occur until the stage of ex pulsion. Originated by reflex action, it is, to a great extent, subject to the volition of the patient, who is thus enabled to materially aid in the expulsion of the fcetus. But, as before stated, this contraction is not indispensable for the happy termination of labor. The vagina, too, is the seat of contractions, which aid in the expulsion of the body of the fcetus, when the head has already escaped from the genital canal, but this con traction is particularly marked at the instant of delivery.
3. Estimation of the Uterine Fbrce.
Efforts have been made to estimate the power of the uterine contrac tions. The uterus may be regarded as a hollow muscle, which, in order to expel its contents, 'Mist first establish an opening through which these contents may pass. The factors cooperating for the formation of this opening are: the effacement, the widening and softening of the cervix, the traction exerted upon the cervix by the uterine contractions, the increase of intrauterine tension due to this traction, and, as a result, the ten dency of the fluid contents of the womb to escape in the direction of least resistance, the cervical orifice. But the uterus also contains the fetus, and thus exercises a duplex action: first, the rupture of the membranes and the cervical dilatation; and, secondly, the expulsion of the foetus.