By induction of labor is meant the bringing on of labor before it has begun of its own accord. If labor is induced between the twenty-eighth and thirty-sixth weeks, when the child still weighs less than five and one-half pounds, it is known as the induction of premature labor. Induction after the thirty-sixth week is the induction of term labor.
Years ago the most common and almost sole reason for inducing labor was contracted pelvis, for if the child was born when quite small it could still pass through the woman’s diminished pelvic diameters. Today, because of the increased safety of Cesarean section and the great fetal mortality caused by the birth of a premature child through the cramped confines of a contracted pelvis, this indication has virtually been abandoned.
We divide the reasons for inducing labor into medical ones, purely obstetric ones, and reasons of convenience. The commonest medical reason is the presence of one of the high-blood-pressure toxemias; the commonest obstetrical reasons are maternal diabetes and immunization of the mother to the Rh factor. In both conditions the baby may die undelivered in the last few weeks of pregnancy. Reasons of convenience may be divided into two categories: the patient’s convenience and the convenience of the physician. The patient may have a pressing social obligation which she is very anxious to honor, such as being a bridesmaid at a wedding; or she may live thirty or forty miles from the hospital and be frightened at the thought of delivering en route. The latter fear is groundless unless she is a multipara. Convenience of the physician may include anticipated absence to attend a medical meeting or a long-planned vacation. Before a doctor will consent to induce labor for either the patient’s convenience or his own, everything must be ideal for its performance. The baby must be at term and term size. It must be a cephalic presentation and the presenting head must be engaged with a soft, short, partially dilated cervix. When such conditions are rigidly met, no difficulties are likely to be encountered by inducing labor.
The induction of labor without a strict medical indication is a highly controversial topic. Be guided by your own doctor’s opinion and practices; do not try to persuade him one way or the other. Your safety and that of your baby are of paramount importance to him, as important to him as they are to you. You may be assured that he will do what he thinks is right and safe for you.
History of Induction
Methods for inducing labor depend on understanding the physiology of labor. It is not surprising, therefore, that the current methods are relatively recent. Until the beginning of the seventeenth century it was generally believed that themade its exit from the uterus much as the chick pecks its way out of the egg, by its own efforts, pushing against the fundus with its feet and cleaving the portals of the womb asunder with the cone-shaped wedge of its hands joined as if in prayer.
It was not until the end of the eighteenth century that the first scientific method for inducing labor, the artificial rupture of the membranes (bag of waters) was originated. (From time immemorial it had been the practice artificially to rupture the membranes during the course of childbirth in order to accelerate it; to induce labor it is done before labor has begun, in the hope of starting the process.) The efficacy of this method depends upon the fact that the simple rupture of the membranes with the drainage of a small amount of amniotic fluid alters the pressure relations within the uterus, so that labor is initiated.
A second method is based on the fact that certain drugs will stimulate the uterine muscle to go into labor. Of the several drugs experimented with the only one to withstand the scrutiny of time is Pituitrin; today we frequently use the synthesized form, Syntocinon. In 1909 Blair Bell of Liverpool found that Pituitrin, the extract of the tiny pituitary gland which lies between the brain and the roof of the mouth, was very efficient in producing contractions of the uterus immediately after delivery, and two years later it was first used to induce labor. Since then Pituitrin has been broken down into its two active components, Pitocin and Pitressin; the former is used in obstetrics. A new Pituitrin-like drug, Spartine, is sometimes given by injection every hour or less to induce labor. It appears to be slightly less effective. With this choice of methods, which does the doctor use today? He is likely to start the procedure with a hot soapsuds enema, which has the tendency to make the uterus more irritable, more sensitive to stimuli. Then he will either puncture the membranes by guiding a pointed instrument through the vagina into the cervical opening and up to the bag of waters, which he spears, or he will administer Pitocin. Sometimes he combines the two techniques, first rupturing the membranes and starting Pitocin forthwith, or he may reverse the order, initiating contractions by Pitocin to be followed soon thereafter by puncture of the membranes. Pitocin for this purpose is usually given intravenously in a continuous, slow, dilute drip, five to seven drops having been added to one pint of glucose water. However, some doctors prefer to give the Pitocin by intramuscular injection, injecting one to two drops every half-hour. Induced labors are normal in all respects, except they are likely to be somewhat shorter, particularly when Pitocin is employed. When the patient is several weeks from term and there is urgent medical need for initiating labor, conditions are usually unfavorable for rupture of the membranes. In these cases Pitocin also may not work. But if one precedes Pitocin by a thorough stripping of the membranes from their attachments near the cervical opening by a finger introduced through the cervix, without rupturing them, Pitocin will have a greater likelihood of starting labor.