Philadelphia Reflections

Pain Phenomena in Obstetrics

Pain Phenomena in Obstetrics

By: Stuart B. Blakely, M.D.

Binghamton, N.Y.

July, 1917

The travail of childbirth is as old as the race. Parturition is the only normal physiological process that is accompanied by pain. It is the most striking phenomenon in the practice of obstetrics. The information available on the subject is most meager and unsatisfactory. These facts justify a further inquiry into these pain phenomena.

Although pregnancy and the puerperium present interesting and important pain phenomena, the time at our disposal limits the discussion strictly to the pain phenomenon of labor. We are not concerned with the cause of their onset. We are not now interested in the motor and reflex phenomena of parturition, except to note that so close is the association of cause and effect in labor pain production that the word “pains” has become synonymous with uterine contraction. This paper will discuss only the subjective symptom of pain occurring during the course of childbirth. Let us, therefore, now proceed to the consideration of the causes, the characteristics, and the localization of the pains of labor.

The chief causes in their production are (1) uterine contraction; (2) consecutive stretching of the cervix with its attachments, the vagina, the perineum, and the vulvar orifice; and (3) pressure of the advancing fetus on the brim, contents, and walls of the pelvis with stretching of its joints. The pain is produced by pressure on or stretching of plexuses, trunks, and end organs of nerves carrying afferent impulses. The nerve supply of the uterus, cervix, and upper vagina is through the sympathetic system, that of the rest of the track and the pelvis through the spinal nerves. Pains of the first stage are due to uterine contraction and cervical dilatation; those of the pressure and stretching exerted by the advancing fetus on the birth canal; those of the third stage, almost solely to uterine contraction. The cases of labor pains, therefore, are near, if not quite, purely mechanical and traumatic. Two other elements that have been cited as possible causes in their production are the forcible contraction of the abdominal muscles most felt at their insertions, and an anemia of the lower spinal cord.

Certain characterizes have been described as being peculiar to the pains of labor. They are associated with forcible uterine contractions. They are more or less intermittent with increasing severity, lengthening duration and lessening intervals as the labor proceeds. They are often called involuntary, a term that really refers to their cause, for all pain is involuntary. The older writers classified them in the four following groups, in order of their appearance: 1. Praesagientes, or foreboding pains that occur during early dilatations up to a diameter of 1 to 2 cm. The French writers' term “touches” biting or annoying pains. 2. Praesagientes, or preparing pains, during which full cervical dilatation takes place. This is the so-called “period of despair,” for toward its close the suffering is often acute. 3. Propellants, or propelling pains. The pain of uterine contraction beside the element of colic peculiar to forcible contraction of any hollow viscus with smooth muscle walls against resistance is more often described as dull and heavy, less often as sharp. The pain of cervical dilatation is usually complained of as breaking. The pain of the pressure and stretching, bursting, shooting, etc., depending somewhat on the tissue or tissues involved at any given moment. These terms are descriptive, but indefinite, as are all terms used to describe painful sensations. We can do no better.

The severity of labor pains is dependent on a variety of factors, many of which are impalpable and unknown. They are profoundly affected by psychical influences, but here again, we are prone to confuse a motor activity with a resulting subjective sensation. If the pains stop, they do so because the uterine contractions have ceased. Individual idiosyncrasy, education, mode of life, and race are determining elements. The strength and suddenness of uterine contraction and the resistance offered to them are important factors in the production of suffering. The severity of the pain presents wide variations. Some labors are nearly painless. Women have given birth without consciousness of its occurrence. At the other extreme is the picture of almost unbearable distress.

The localization of the pains of labor is of great interest. It opens up the whole subject of somatic and visceral pain, a vast and nebulous realm, to enter which is to be lost. However, to better understand the localization of some of the pain phenomena of labor, it is essential to memory the nerve supply of the uterus, birth canal, and pelvis, and to review the peripheral sensory distribution of the segments of the spinal cord involved.

It is generally admitted that the viscera are insensitive to pain. This means that stimuli, ordinarily painful when applied to the periphery, have no corresponding effect when applied to viscera. Pain can be produced in viscera, however, if the stimulus is “adequate,” a highly necessary, but also highly indefinite term. The pain thus produced is not felt in the viscus, but in some area on the periphery of the body. It is accordingly called “referred” pain. The peripheral area in which it I referred, is connected with the same segment or segments of the spinal cord in which it is referred, is connected with the same segments or segments of the spinal cord in which the impulse from the stimulated viscus is received. To summarize stimulation of a viscus, adequate to produce pain, create an impulse that passes through the sympathetic to certain definite segments of the spinal cord, and is felt subjectively in the peripheral sensory distribution of these segments.

To the best of belief, the body of the uterus is connected through the sympathetic with the tenth, eleventh, and twelfth dorsal, and the first lumber segments of the spinal cord. The peripheral sensory distribution of these segments is the lumbar region of the back and the lateral and anterior aspects of the abdomen from about the level of the umbilicus down onto the thighs. Here is felt the pain produced by uterine contraction. The cervix is connected the second, third, and fourth sacral segments of the cord. The peripheral distribution is the sacral and coccygeal region extending onto the buttocks and down the back of the thighs. In this area is felt the pain of cervical dilatation. The foregoing segmental connections and distribution follow, in the main, the scheme of Henry Head.

The nerve supply of the pelvis, vagina, perineum, and vulva is of spinal origin, chiefly through the pubic nerve. Pain originating hereby pressure or stretching is felt locally in the parts named, or in the distribution of nerves derived from the sacral plexus.

It is unnecessary to describe stage by stage the localization of the pains of labor. It can be easily determined. During the first stage sometimes, the pain of cervical dilatation predominates, at other times that of uterine contraction. For example, compare the severe sacral pain complained in many cases of dry labor, with the localization of the pain in a case of a fully dilated cervix but with a head not engaged or obstructed at the brim. In the second stage, the pain of a uterine contraction is sometimes added a slight pain produced locally by the extrusion of the placenta.

The study of all pain is very involved and beset with great difficulties but is worthy of great effort. Our knowledge of it is fragmentary and incomplete. This paper has endeavored, briefly and in an elementary manner, to discuss the causes, the characteristics, and the localization of the pains of labor. It is presented, not with the idea of being exhaustive or without mistakes, but to bring to your thoughtful attention a subject of which the profession hears so much, but really knows so very little.

Originally published: Friday, July 06, 2018; most-recently modified: Friday, May 31, 2019