The Elective Induction of Labor

The Elective Induction of Labor ROBERT A. KIMBROUGH, JR., M.D., F.A.C.S. * EDWARD H. BISHOP, M.D., F.A.C.S. **

ELECTIVE induction of labor in selected patients has been practiced by some obstetricians for many years but without acceptance of this procedure by the majority. General acceptance during the past few years has led to much enthusiasm for a procedure which seems to be advantageous for both the obstetrician and the patient. Unfortunately, enthusiasm often results in promiscuous and indiscriminate usage. While the authors, as a result of their experience, are convinced of the benefits of elective induction of labor, they make a plea that this wave of enthusiasm be restrained by good judgment in order to prevent this valuable addition to the armamentarium of the obstetrician from falling into disrepute. This is certain to occur unless conservatism is the ruling principle in elective induction of labor. An analysis of the experience at the Pennsylvania Hospital during the past three years is presented and serves as a basis for demonstration of the value of conservatism.

INCIDENCE

From February I, 1952 to April 1, 1955, 10,000 patients were delivered at the Pennsylvania Hospital and 1144 of these deliveries followed the purely elective induction of labor. Inductions performed because of a definite obstetric or medical indication are not included in this series. As shown in Table 1, the incidence of induction of labor was 1.2 per cent on the Ward Service and 22.9 per cent on the Private Service. SELECTION OF PATIENTS

The difference between satisfactory and unsatisfactory results is almost wholly dependent upon the proper selection of candidates for elective induction of labor. Minor variations in technique make little differ-

* ProfessQ1" of Obstetrics and Chairman of the Department, Graduate School of Medicine, University of Pennsylvania; DirectQ1", Division of Obstetrics and Gynecology, Pennsylvania Hospital; Chief of Gynecology and Obstetrics, Graduate Hospital, Philadelphia. ** Associate in Obstetrics and Gynecology, Graduate School of Medicine, University of Penn8ylvania; Assistant Obstetrician and Gynecologist, Pennsylvania Hospital; Visiting Ob8tetrician and Gynecologist, Methodist Episcopal Hospital, Philadelphia. 1809

1810

Robert A. Kimbrough, Jr., Edward H. Bishop

ence provided the patients are comparably selected. Study of this series revealed many important points essential to proper selection. Table 1 INCIDENCE OF INDUCTION

Deliveries ............... Inductions ..... Percentage .........

PRIVATE

WARD

TOTAL

4764 1083 22.9

5236 61 1.2

10,000 1,144

11.4

1. Parity The average duration of labor of both nulliparous and multiparous patients is presented in Table 2. Table 2 DURATION OF LAB OR NUMBER OF PATIENTS

AVERAGE DURATION (Hours)

1144

4.7 7.7 4.0

All patients ................... . Nulliparas ... . Multiparas ........ .

175 969

The average duration of only 7.7 hours in the nulliparous group is not unexpected as these patients constituted a selected group whose labor should be short and uneventful. Nevertheless, as shown in Table 3, 37 per cent of the nulliparous patients were in labor over eight hours. Table 3 DURATION OF LABOR

Less than 8 hours ....... . More than 8 hours ...... .

MULTIPARAS (Per cent)

NULLIPARAS (Per cent)

91 9

63 37

When labor following induction is of such duration, there is little indication or advantage in elective induction. Contrary to the experience with multiparous patients, even the most favorable pelvic findings before the initiation of the induction did not always result in a labor of short duration for the nullipara.

The Elective Induction of Labor

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2. Pelvic Findings

Before reaching a decision regarding the eligibility of a patient for induction of lab or it is necessary to ascertain certain essential information regarding the cervix and the presenting part of the fetus. During the development of this series it became obvious that rectal examination was an unsatisfactory method to obtain accurately this essential information. Instead, reliable information can be obtained only by vaginal examination which should be performed before initiation of the induction and preferably before admission of the patient to the hospital. The importance of adequate dilatation and effacement of the cervix and proper station of the presenting part is shown in Table 4. Table 4 COMPARISON OF EFFECTS OF FAVORABLE AND UNFAV0RABLE PELVIC FINDINGS ON DURATION OF LABOR IN MULTIPARAS

DURATION

Less than 8 hours .. . More than 8 hours ...... .

FAVORABLE

(Per cent)

100

o

UNFAVORABLE

(Per cent) 85 15

Favorable pelvic findings were determined as vertex presentation at station minus 1 or lower, with the cervix not less than 3 cm. dilated and not less than 60 per cent effaced. In instances in which induction of labor was carried out in spite of unfavorable pelvic findings, the duration of labor was longer and the incidence of complications was increased. Experience revealed also the importance of the consistency and position of the cervix in relation to the success of induction of labor. It is difficult to employ numerical gradations of the changes in consistency of the cervix as pregnancy approaches term. Only experience can teach the obstetrician to appreciate the softening and increase in elasticity of the cervix which are consistent with "ripening" and consistent with successful induction. The cervix which lies in the posterior vaginal vault is seldom associated with findings favorable for induction; the favorable cervix is almost always in the anterior position. In summary, experience reveals that if there is any question concerning the suitability of the pelvic findings, the induction of lab or should be deferred. More often than not the patient will not go into lab or during this waiting period and the pelvic findings subsequently may be more suitable for elective induction of labor. 3. Expected Date of Delivery

The too frequent vagaries and faulty memories of patients concerning their menstrual histories combined with the natural variation in time of

Robert A. Kimbrough, Jr., Edward H. Bishop

1812

conception and duration of pregnancy predicate against using the calculated date of delivery as the optimal time for induction of labor. Previous experience revealed that it is seldom possible to determine the optimal changes in the cervix more than 24 to 72 hours befor~ the spontaneous onset of labor. The deliberate scheduling of patients for elective induction of labor five to ten days in advance can only be condemned as its practice leads to unsatisfactory results. 4. History of Previous Pregnancies

Potential complications of labor constitute contraindications to the elective induction of labor. The tendency toward the gradual increase of fetal size which is associated with increasing parity must always be considered in selecting patients for induction of labor. TECHNIQUE OF INDUCTION

Preparation of the Patient

The patient should be admitted to the hospital a few hours before the anticipated time of initiation of the induction. Under certain circumstances it may be desirable for the patient to be admitted the evening before. This allows for a night of adequate rest with the help of mild sedatives and prevents the accidental or thoughtless ingestion of food shortly before an anticipated anesthesia. Immediately preceding the initiation of the induction the patient should be prepared according to the usual hospital routine. Initiation of Labor

Uterine contractions may be initiated by one of three methods: (1) amniotomy alone, (2) amniotomy followed by divided doses of intramuscularly administered Pitocin, or (3) amniotomy either preceded by or followed by Pitocin by the continuous intravenous drip method. Each method has certain advantages and disadvantages and warrant individual conl'lideration. 1. Amniotomy Alone. If the circumstances are ideal, artificial rupture of the membranes will be followed most often by the spontaneous onset of labor. If amniotomy alone is used, the ensuing uterine contractions are more physiological than those which follow stimulation by an oxytocic drug, and the possibility of tetanic contractions of the uterus may be avoided. This advantage may be offset by the length of the latent period from the time of amniotomy to the onset of uterine contractions. In this series this period varied from 10 minutes to over 12 hours. In those cases in which a long latent period occurs there is little advantage of elective induction of labor over that of spontaneous onset.

The Elective Induction of Labor

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2. Amniotomy Combined with Intermittent Doses of Intramuscular Pitocin. If labor does not follow amniotomy within a reasonable period of time, uterine contractions may be stimulated by small doses of Pitocin administered intramuscularly. Thus a prolonged latent period may be avoided and the duration of the induction reduced to a minimum. This method has the advantage of simplicity as compared to administration of the drug by the intravenous route. The most important disadvantage is that once the Pitocin has been administered there is no adequate method to reduce its total pharmacological effect until the drug has exerted its entire action. On rare occasions, even with small doses, this may result in a prolonged tetanic contraction of the uterus with possible damage to the fetus. If repeated doses are necessary, the action of the uterus is often as intermittent as the periods of administration. Moments of contractions of the uterus are followed by intervals of relative inactivity which in no way simulate the physiological pattern of true labor. 3. Amniotomy Either Preceded by or Followed by the Use of Pitocin Intravenously. This method has the advantage of simulating true labor to a greater degree than does the use of Pitocin intramuscularly. The effect is minimal but continuous. If untoward results occur, the effect of the oxytocic drugs may be stopped almost instantaneously by discontinuing the intravenous drip. In order to avoid confusion it is suggested that hospital staffs standardize the dilution of Pitocin and the maximal rate of administration. A safe but still effective dilution is 1: 1500, with the rate not to exceed 30 drops per minute. Among the disadvantages of this method are the discomfort of the patient resulting from immobilization of an extremity, difficulty with transportation of the patient without disturbing the intravenous set, and the necessity for constant observation in order to insure that the drip remains at a constant rate. The most efficient form of induction in respect to safety and minimal duration of labor is amniotomy followed by the use of Pitocin administered intravenously as described above. The use of Pitocin in this same manner but before amniotomy does have the advantage of providing an opportunity for the observation of the response of the uterus to the oxytocic drug without "burning your bridges behind you." This probably is not necessary if the patient has been selected carefully and fulfills all of the previously defined criteria. Inasmuch as amniotomy is not without danger of certain complications, it should be performed by the attending obstetrician rathe!' than be delegated to someone of less experience such as a resident or interne. Since this is an elective procedure, since the subsequent labor is frequently of short duration and since the artificial initiation of labor is not entirely free from potential complications, it is the responsibility of the obstetrician to remain in constant attendance during the entire procedure. If he cannot fulfill these obligations there is no justification for the elective induction of lab or.

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Robert A. Kimbrough, Jr., Edward H. Bishop MANAGEMENT OF LABOR

Experience developed during this series of inductions dictated only two alterations in the usual methods of the management of labor. The first was the administration of analgesia at the time of the initiation of the induction instead of waiting until the patient became uncomfortable, or even until labor had become well established. This early administration of sedatives minimized the apprehension of the patient during the early stages of the induction. Since labor was usually of short duration, waiting until the patient became uncomfortable frequently made it too late for either the safe or the effective action of the analgesic drugs. The second alteration in technique which appeared to be important was the continuation of the intravenous Pitocin for 30 to 60 minutes after the end of the third stage of labor, in order to minimize the likelihood of postpartum hemorrhage. EFFECT OF STANDARDS

For the purpose of determining the effect of the previously deseribed criteria for selection of patients, the cases comprising this series have been divided into two groups. Group A is comprised of those patients who were considered ideal candidates for induction in that they were multiparous patients with normal obstetrical histories. In all instances before induction the presenting part was a vertex at station minus 1 or lower, the cervix was soft, not less than 60 per cent effaced and not less than 3 cm. dilated. Group B consisted of all other cases of elective induction of labor which did not fulfill these conditions. The methods of delivery for both groups are listed in Table 5. Table 5 METHOD

m'

DELIVERY

GROUP A

Number Spontaneous .. Low forceps ... Mid forceps .. Breech .. . Cesarean ..................... . TOTAL . . . . . . . . . . . . . . .

GROUP B

Per cent

266 175

59.6 39.2

o

0.0 0.2

4

1

446*

1.0

100.0

N umber

Per cent

142 523 17

20.2 74.5

702*

100.0

18 2

2.4

2.6 0.3

* Includes two sets of twins. While elective outlet forceps are almost routine in the hospital, it must be conceded that the lower operative incidence in Group A indicates better results for both the mother and the baby.

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The fetal complications in both groups are listed in Table 6. Table 6 FETAL COMPLICATIONS GROUP A

Variation in fetal heart sounds ... Prematurity ................... Fetal loss ..................... Corrected fetal loss· ............

GROUP B

Number

Incidence (Per cent)

Number

Incidence (Per cent)

9 1 2 0

2.2 0.2 0.4 0.0

13 4 5 2

1.8 0.6 0.7 0.3

* Corrected to exclude babies dying of either erythroblastosis or congenital lesions incompatible with life. The incidence of prematurity and both the gross and the corrected fetal loss are all lower in the group having the most favorable pelvic findings at the time of the initiation of the induction. CONCLUSIONS

1. After certain criteria have been fulfilled, amniotomy alone or in combination with the administration of Pitocin constitutes a satisfactory method for the elective induction of labor. 2. In order to obtain the best results, elective induction of labor should be limited to multiparous patients with a vertex presentation and with cervical changes which are indicative of the imminent onset of labor. 3. Elective induction of labor can be justified only by results which do not reveal any untoward effects on either the mother or the baby. 4. It is imperative to preserve a conservative attitude in relation to this procedure in order to prevent the unnecessary complications which are certain to follow a more radical approach. 807 Spruce Street Philadelphia 7, Pennsylvania