It is natural to ask what purpose is served by the pain associated with labor; and a moment's reflection will make it clear that one reason for the discomfort is the warning which it gives of the approach of birth. If the mother were not thus cautioned, she might be delivered under very awkward circumstances, and even under such conditions that occasionally the infant would perish the instant it was born. All mammals suffer in giving birth to their young, though with quadrupeds the period of suffering is shorter, for the upright posture of man has changed the shape of the pelvis, rendering birth somewhat more difficult. Anyone who observes the lower animals preparing for delivery will be convinced that they also are responding to pain, the most compelling call of nature.
That the suffering is at all essential to the mother's love for her child I cannot believe. Under certain circumstances, as for example when the Cesarean operation is performed before the onset of labor, the delivery is painless; yet I have never known a mother less devoted to her child on that account. Biology throws no light upon the relation of the "curse of Eve" to present-day confinements.
THE CAUSE OF LABOR.—It is evident that, in a general way, the muscular contractions of the womb cause the birth of the child; but before we thoroughly understand the act, science must discover what stimulates the muscle to contract. Although careful research has thus far failed to disclose the source and character of the stimulus, it has taught many properties of the contractions themselves. Their force has been measured and found to increase as the end of labor is approached; the pressure they exert varies between nine and twenty- seven pounds. We also know that the patient can neither hasten nor delay the contractions voluntarily. Strong emotions are believed to accelerate them at times, and we find a very extraordinary illustration of this effect recorded in I Samuel, IV, 19, where we read: "Phineas' wife was with child, near to be delivered; and when she heard the tidings that the ark of God was taken, and that her father-in-law and her husband were dead, she bowed herself and travailed; for her pains came upon her." On the other hand, and much more familiarly, excitement checks the contractions after they have begun. Every obstetrician has heard patients say that with his arrival the pains died down. Yet such an influence is never permanent; the contractions soon reappear, and labor advances as though no interruption had occurred.
For the artificial induction of labor, the physician has at his disposal means that resemble the method sometimes employed by nature. Suitable appliances introduced into the womb provoke contractions, and labor proceeds step by step as if the stimulus were a normal one. Nature does not, however, ordinarily employ mechanical irritation to start the uterine contractions. The initial factor is more remote and, as I have said, is not yet well understood.
Since, as everyone admits, delivery occurs with conspicuous regularity about the end of the fortieth week of pregnancy, and pregnancy corresponds, therefore, to ten menstrual cycles, some have been led to believe that labor and menstruation have a common basis. The truth of this supposition, however, must be doubtful until we know the cause of menstruation. Yet it is a matter of common observation that the uterus becomes unusually irritable about the time when the tenth menstrual period would be due. Strong purgatives administered with other drugs on or after the calculated date frequently bring about delivery, whereas previous attempts of this kind prove unsuccessful. To account for this peculiar irritability of the uterus about the fortieth-week of pregnancy, microscopical changes in its tissues have been suggested but sought in vain. Nor will the distention of the organ explain it.
A great many theories have been offered to explain the causation of labor, but they have now only an historical interest. To-day we are just beginning to learn the correct methods of studying the problem. The experience of ages has firmly established the fact that the fetus is expelled when ready to enter the world, or as we say, when it has become mature. But how does the fetus assert its maturity? There is the kernel of the matter; that is the real problem, a problem for the solution of which, happily, we possess better facilities than have heretofore existed. One solution that has been suggested assumes that the fetus loses ultimately its power to assimilate the nourishment provided through the mother's blood. In consequence, it is argued, the material which previously enabled the fetus to grow now collects— in the maternal circulation, stimulating the womb to contract.
A part of this explanation, namely, that the material which stimulates the muscle fibers, whatever it may be, is a chemical substance and that it circulates in the mother's blood, is almost certainly true. There are, however, very weighty reasons for believing that this substance has not the character of food. A more plausible supposition is that the fetus produces this material in the course of its natural living processes, and the substance would accordingly be a waste-product.
THE COURSE OF LABOR.—The current view that labor begins in the early evening and generally ends during the night is incorrect. This impression has grown out of the fact that the whole process frequently consumes twelve hours and must in such an event include some part of the night. Statistical evidence indicates that almost as many births occur at one hour of the twenty-four as another; to be precise, only five per cent. more children are born between 6 P.M. and 6 A.M. than between 6 A.M. and 6 P.M.
As already pointed out, labor commonly begins with transient discomfort in the lower part of the back. At first the uterine contractions are far apart; they last but a moment and cause only twinges of pain. Gradually, the preliminary contractions give place to others of more definite character, which appear at intervals of five to ten minutes. Estimates of the total length of labor will vary according as one counts from the first warning or from the advent of typical contractions which we hear called "pains of the right kind." These generally continue for about four hours, and this period represents the average length of time the physician remains constantly with his patient. Estimates which include the initial symptoms are longer, varying from ten to eighteen hours. Prolonged labors are rare; and extremely short labors are also infrequent, though now and again it will be only an hour or two from the very first pain until the child is born.
To predict absolutely the length of labor for any particular patient is impossible. The averages calculated from large groups of cases have no more than a broad scientific interest; when applied to any individual they are apt to be very misleading. Thus, from statistics we should expect the first labor to be longer than subsequent ones, but we are often surprised by an unusually rapid delivery.