Induction of Labour: Indications and Methods

""'"

'SYMPOSIUM""""

INDUCTION OF LABOUR: INDICATIONS AND METHODS William Fraser, MD, FRCSC, MSc, 1 Michel Boulvain, MD, PhD cand.,2 1Associate Professor, 2Fellow, Maternal and Fetal Medicine, Department of Obstetrics and Gynaecology, Laval University, Centre hospitalier universitaire de Quebec, Pavillon Saint~Franc;ois d' Assise

ABSTRACT

This is the first article in aseries reparting the proceedings of an international seminar on labour induction whieh was presented at the Annual Meeting of the SOGC in Quebee in}une 1996. The objeetives of this seminar are (1) to review the seientifie basis forreeommendations on labour induction, including post-term pregnancy and prelabour rupture of the amniotic membranes at term, and (2) to review reeent teehniques for labour induction. This first artiele will review the most frequent indications for labour induction and will diseuss the evidence eonceming the management of the post-term pregnancy. I twill then review currently available teehniques for eervieal ripening and discuss the use of prostaglandin gel for labour induction. RESUME

Il s' agit du premier d' une serie d' artieles faisant etat des travaux d' un eolloque international sur le deelenchement du travail organise dans le eadre de l' assemblee annuelle de Ia SOGC ii Quebee en juin 1996. Ce eolloque visait, premierement, ii examiner les fondements seientifiques des reeommandations sur le deelenchement du travail, y eompris en eas de grossesse prolongee et de rupture prematuree des membranes amniotiques ii terme et, deuxü~mement, ii examiner les teehniques reeentes de deelenchement du travail. Ce premier artiele porte sur les indications les plus frequentes de deelenchement du travail et sur les donnees au sujet de Ia eonduite ii tenir en eas de grossesse prolongee. On y traite ensuite des teehniques actuelles de murissement eervical et de l' utilisation d' un gel de prostaglandine pour deelencher le travail.

J SOGe 1996;18:1125-31 KEY WORDS

Induction oflabor, postterm, prostaglandins, oxytocin, overview. Received on April 10th, 1996. Revised and accepted on April 18th, 1996.

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, , , pregnancy (6.2% to 9.3%). It is possible that this may, in part, be a reflection of the effect of the implementation of the SOGC guidelines on the management of the postterm pregnancy.J However, during the same period, the overall proportion of inductions increased similarly (from 18.6% to 27.9%), possibly reflecting a more liberal attitude to induction in general. A similar trend has been noted in anumber of Canadian tertiary care hospitals. 4

INTRODUCTION

When spontaneous labour is compared in randomized controlled trials to elective induction before 41 weeks, the latter is associated with increases in the requirement for analgesia, and in the rate of operative vaginal delivery.l Observational studies suggest that there is a trend toward an increase in the rate of Caesarean section, particularly among nulliparous women with unfavourable cervices. 2 Induction often requires continuous electronic fetal monitoring, which reduces the woman's mobility. All available methods of induction of labour have associated medical risks. The decision to induce labour should only be made when the risk of continuing pregnancy outweighs the risks of induction. For certain clinical conditions, including severe pre-eclampsia, the decision to induce labour is straightforward. For other conditions including post-term pregnancy, the point at which the risk of continuing pregnancy outweighs the risks associated with induction is often not clear-cut. Furthermore, the risk to benefit ratio may be influenced by the methods used to induce labour, and by the methods used to assess fetal wellbeing serially in cases of expectant management.

POST-TERM PREGNANCY

Post-term pregnancy is the most frequent indication for induction. With routine ultrasound dating of pregnancy, the frequency of 42+ week gestations should be no greater than four percent. A large Scandinavian study (Table 2) provides data on the perinatal mortality risk in relation to gestational age. s It should be noted that the curve is U-shaped and that only after 42 weeks does the risk approach that observed at 39 weeks. There is a near doubling of risk at 43+ weeks. The Canadian Post-Term Pregnancy Trial demonstrated that the fetal morbidity risk associated with serial antenatal monitoring was not greater than the risk of prophylactic induction of labour. 6 With respect to mortality, two perinatal deaths occurred among the 3,407 INDICATIONS FOR INDUCTION OF babies in the trial, both in the expectant management LABOUR group. Induction rates vary widely from hospital to hospital. A meta-analysis of 12 trials comparing expectant The rate of induction of labour at H6pital St. Fran~ois management to induction of labour in post-dates pregd'Assise in Quebec City in the year 1991 to 1992 was nancies is reported in the Cochrane database. 1 Eight peri18.6 percent. The most frequent indications for labour natal deaths occurred in these trials, seven in the induction in this hospital are listed in Table 1. Since expectant management group. This analysis suggests that 1991, there has been a 50 percent increase in the proa policy of labour induction at 41 + weeks may be assoportion of women undergoing induction for prolonged ciated with a slight reduction in the risk of perinatal mortality. When expressed as the "number needed to treat" to prevent one adverse outcome, 500 inducTABLE 1 tions would need to be performed to prevent one FREQUENCY OF INDUCTION OF LABOUR BY INDICATION AMONG perinatal death. NON-REFERRED WOMEN, HÖPITAL ST-FRANC;:OIS d'ASSISE The results of this meta-analysis, however, (1991-92 compared to 1994-95) should be interpreted with caution. One small 1991 -92 1994-95 study which contributed two of the seven perinaN= 1962 Perce nt N=1944 I Percent tal deaths in the expectant group was carried out Prolonged pregnancy 120 6.2 181 9.3 in the pre-fetal assessment era. Should a policy of 3.5 92 4.7 PROM 68 Hypertension, Pre-eclampsia 44 2.2 23 1.2 labour induction be associated with a true reducFetal Macrosomia 20 1.0 25 1.3 tion in the risk of perinatal mortality, the magni50cial Indication 17 0.9 42 2.2 tude of this effect is likely to be smaller in the 96 4.8 178 9.2 Other context of currently available methods of perinatal 362 18.6 544 27 .9 Total assessment.

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20% of bone mass has been lost by the average postmenopausal woman FOSAMAX 10 mg daily produced statistically significant and clinically important increases in BMD at the hip, spine. and wrist (ultradistal forearm) relative to placebo at three years (p:50 001) 1.2 t: Combined data from two large. identically designed, double-blind , placebo-controlled, three-year multicenter studies in 994 women with osteoporosis, defined as low bone mass. 397 of whom received placebo and 196 of whom received FOSAMAXII> 10 mglday. To ensure an adequate calcium intake. all patients were supplemented with 500 mg of calcium per day.' I Liberman UA eta!. Effect of oral alendronate on bone mineral density and the incidence of fractures in postmenopausal osteoporosis . N Eng!! Med 1995;333(22) 1437-43 2. Data on file, Merck Frosst Canada Inc . 1\vo double-blind, randomized, placebo-controlled. parallelgroup, multicenter studies to evaluate the safety and effect on bone density of daily oral MK-217 for two years in osteopenic postmenopausal women . with a one-year open treatment extension IProtocol No. 035 (US) and 037 (lnternationai)(-Three Year Data

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, , , management of premature rupture of the membranes at term will be addressed in aseparate article in this symposium. Induction of labour for medical or psychosocial indications are probably evaluated best on an individual basis. Women who are experiencing serious psychological distress in late pregnancy may benefit from induction of labour, providing the cervix is favourable. Medical indications which are relative should also be assessed on an individual basis. For a woman with an unfavourable cervix, in the absence of a clear-cut indication for induction, waiting for spontaneous labour is probably the best approach.

TABLE 2 BA5ED ON 157,677 BIRTH5 WITH CERTAIN EXPECTED DATE OF DELIVERY, 5WEDEN, 1977 AND 1978

-

Number of births

Perinatal deaths per 1,000 births

38

16,325

7.2

39

34,390

3.1

40

44,986

2.3

41

32,527

2.4

42

13,883

3.0

2,227

4.0

Gestation age (weeks)

43+

Reproduced with Permission; Bakketeig LS. Holfman JH. Harley EE. The tendency to repeat gestational age and birth weight in successive births. Am J Obstet GynecoI1979;13S:1086-1103.S

CERVICAL RIPENING-USE OF PROSTAG LAN DI NS

A reduction in Caesarean risk was observed in association with a policy oflabour induction in the Post-term Tria1. 6 This appears to belie the view that induction increases Caesarean risk. However, this observation should also be interpreted with caution. Prostagiandin gel was only available to women in the induction group. The approximately one-third of those in the expectant group who went on to induction did not have access to gel. A simulation based on the use of prostaglandins in both groups in the Canadian Post-term study8 resulted in a reduction in the risk difference, with the estimated frequency of Caesarean section of 23.3 percent in the expectant group versus 20.8 percent in the induction group. Based on this risk difference, 40 inductions would need to be performed to avoid one Caesarean sec ti on. Most of the excess in Caesarean sections that occurred in the expectant management group were due to "fetal distress." Whether such strategies as fetal scalp blood pH assessment and amnio-infusion in patients with suspected "fetal distress" would have reduced or eliminated this difference is open to speculation.

The Bishop score is a pelvic scoring system which is a useful predictor of the success of induction attempts. 9 Bishop noted that, with ascore of nine or more, the risk of failed induction was minimized, hence the importance of the concept of ripening the cervix for women whose score is unfavourable prior to attempting induction. Oxytocin, while effective for labour induction, is an ineffective method for cervical ripening. 10 Prostaglandins (PGEz and PGFzo:) have been demonstrated in clinical studies to be effective medications for cervical ripening. Prostagiandin acts directly on the cervix. Its ripening effects are not primarily mediated by uterine contractions. Prostaglandins result in biochemical and biophysical changes which lead to softening of the cervix. Intracervical PGEz (Prepidil 0.5 mgs) is currently the preferred method for cervical ripening. Intracervical administration has the advantage over the oral or intravaginal routes of minimizing gastro-intestinal side-effects. ll T able 3 is a summary of the meta-analysis reported in the Cochrane database comparing prostaglandins (all routes) to placebo or "no treatment" for cervical ripening. 12 Prostaglandins for cervical ripening are associated with a statistically significant reduction in the rate of Caesarean section, instrumental vaginal delivery, and failed induction. The proportion of women not delivered within 12 hours of commencing labour induction is dramatically reduced when the cervix is prepared with PG. Although there is some risk of both hyperstimulation and fetal heart abnormality associated with the use of pros tag land in for cervical ripening, the risk of neonatal compromise does not appear to be increased.

OTHER INDICATIONS FOR INDUCTION OF LABOUR

Although suspected fetal macrosomia (by ultrasound estimation of fetal weight) is recorded as an indication for induction in some centres, there are no data to indicate that induction reduces the risk of Caesarean section or neonatal trauma in this group. For diabetic pregnaneies, unless there are fetal abnormalities detected by biophysical assessment, patients should be permitted to go into spontaneous labour at term. The subject of

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reduction in the proportion of patients treated with FOSAMAX® experiencing one or more vertebral fractures relative to those treated with placebo in pooled analysis (5-20 mg) (p =0 . 0 3 ) '·~

Low bone mass is a major predictor of increased risk of osteoporot ic fractures 3 6 2% (22/355) of patients who rece1ved placebo and 3 2% ( 17/526) of patients who received FOSAMAX• (5 or 10 mg for 3 years or 20 mg for 2 years followed by 5 mg for I year) 1 tt Nonvertebral fractures occurred in 9.6% (381397) of patients who received placebo and 7 5% (45/597) of patients who received FOSAMAX• (5 or 10 mg for 3 years or 20 mg for 2 years followed by 5 mg for I year) A trend towards a reduced number of nonvertebral fractures was observed in the patients treated with FOSAMAX• I 3 Consensus Development Conference D1agnosis. prophylaxis. and treatment of osteoporosis.Am ) Med 1993.94 646-9 FOSAMAX•. like other bisphosphonates. may cause local irritation of the upper gastrointestinal mucosa Esophageal adverse experiences. such as esophagitis. esophageal ulcers and esophageal erosions have been reported in patients receiving treatment with FOSAMAX•. In some cases these have been severe and required hospitalization Healthcare professionals should therefore be alert to any signs or symptoms signaling a possible esophageal reaction and patients should be instructed to discontinue FOSAMAX• immediately and seek medical attention if they develop dysphagia. odynophagia or retrosternal pain FOSAMAX• is contraindicated in patients who have abnormalities of the esophagus which delay esophageal emptying such as stricture or achalasia. who are unable to stand or sit upright for at least 30 minutes. who are hypersensitive to any component of this product. who are hypocalcemic or who suffer from renal insufficiency (creatinine clearance< 35 mUmin)

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, , , TABLE3 A META·ANALYSIS OF THE EFFECT OF PROSTAGLANDINS (ANY ROUTE) FOR CERVICAL RIPENING ON LABOUR AND PERINATAL OUTCOMES

I---

No. Trials

Odds Ratio

Labour onset du ring ripening

30

"Induction failure"

18

Hypertonus/hyperstimulation

12

Effect on

95 Percent CI LO

HI

7.35

6.16

8.77

0.31

0.25

0.39

1.76

1.11

2.80

7

0.24

0.15

0.37

Caesarean section

35

0.81

0.68

0.97

Instrumental vaginal delivery

19

0.74

0.59

0.95

Fetal heart rate' abnormalities'

16

1.31

0.99

1.72

7

0.89

0.47

1.71

Low Apgar score at 5 minutes

16

0.64

0.33

1.25

Perinatal death (excI. malformations)

16

0.68

0.12

, 3.92

Not delivered 12 hours after induction

Post·partum haemorrhage

I

-

I

(35 trials reviewed)

Adapted with the permission of the Editor, Cochrane Collaboration Pregnancy and Childbirth Database.

TABLE4 A META·ANALYSIS OF THE EFFECT OF ANY PROSTAGLANDINS (ANY ROUTE) FOR LABOUR INDUCTION, ON LABOUR AND PERINATAL OUTCOMES Effect on

-

No. Trials

Odds Ratio

-

95 Percent CI LO

HI

-

0.89 7.23

"Induction failure"

24

0.74

r--' 0.62

Gastro·intestinal side effects

12

4.36

2.62

Hypertonus/hyperstimulation

22

3.21

2.13

4.84

4

0.28

0.14

0.56

12

0 .43

0.32

0.58

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Analgesia

I

as the catheter tip is withdrawn to the externaios. Caution should be exercised to avoid injection into the lower uterine segment as this increases the risk ofhyperstimulation. It is important not to confuse Prepidil gel for intracervical use with Prostin Ez vaginal gel which comes in doses of one and two mg and is used for labour induction. Following administration, uterine activity and the fetal heart are monitored continuously for at least one hour. The dose may be repeated in six hours if a satisfactory Bishop score has not been obtained, and if uterine activity is minimaL Contra-indications to the use ofPGEz gel for cervical ripening are similar to the contra-indications for induction of labour in generaL Intracervical gel should not be used in the presence of ruptured membranes. The product monograph lists parity > five as a contra-indication. Asthma is a theoretical rather than a documented complication of PGEz use. Several centres in North America, including ours, use PGEz for patients desiring vaginal birth after Caesarean section (VBAC) who require cervical ripening prior to induction. I3 Gastro-intestinal side effects and pyrexia can occur but both are rare. INDUCTION OF LABOURCOMPARISON OF PGE 2 TO OXYTOCIN

For women with a favourable Bishop score (whether achieved spontaneously or by medical 0.72 1.21 0.93 Caesarean section 30 means), several options are available when induc0.60 0.99 0.77 Instrumental vaginal delivery 17 tion is necessary: amniotomy alone; oxytocin alone; 0.64 1.51 0.98 Post·partum haemorrhage 10 0.58 2.06 1.09 Low Apgar score at 5 minutes 13 amniotomy and oxytocin; oral prostaglandins; vagi0.77 , 19.14 3.85 Perinatal death (excl. malformations) 15 nal prostaglandins. Amniotomy alone would appear (30 trials reviewed) to be an attractive approach in same situations. Con_. Adapted with the permission of the Editor, Cochrane Collaboration Pregnancy and trolled trials, however, suggest that early adminisChildbirth Database. tration of oxytocin following amniotomy reduces the risk of operative delivery compared to oxytocin alone. '4 Approximately 30 to 40 percent of women receiving The controlled trials evaluating different medical intracervical PGEz will go on into labour during the approaches to induction tend to involve small sampie process of ripening. sizes. Again, meta-analysis provides an indication of the The method of administration of PGEz is simple. relative effectiveness of the different approaches. Trials Prior to administration, a reactive Non-Stress Test have compared oxytocin to oral prostaglandins and (NST) is required. The product comes with an applicaoxytocin to vaginal PG. 1S,16 There have been no direct tor tip which is inserted under direct visualization into comparisons of oral to vaginal PG. The acceptability of the cervical canal, up to but not beyond the internalos. oral prostagiandin is probably less than for vaginal, as The viscous gel (containing O.5mg ofPGEz) is injected No vaginal delivery within 24 hours

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, , , gastro-intestinal side effects (vomiting and diarrhoea) are more frequent and severe with the former. Overall, prostaglandins (any route) appear to result in a reduction in the risk of operative delivery when compared to oxytocin (Table 4) .12 The proportion of women not delivered within 24 ho urs is significantly reduced (Odds Ratio = 0.43). The frequency of analgesia use is reduced with PG as compared to oxytocin.

8.

9. 10.

CONCLUSION

This article has reviewed the evidence regarding different indications for induction of labour. Data concerning the effectiveness of different methods of labour induction also have been considered. Our local data indicate an increase in the proportion of women being submitted to labour induction. The increase in induction rate was observed not only for post-term pregnancy but also for other indications, including social indications. While the optimal rate of induction is difficult to define, the dramatic increase in recent years provides grounds for concern. Local policy makers and care providers must develop mechanisms to scrutinize the quality of care in regard to the indications and methods for labour induction. REFERENCES 1.

2.

3. 4. 5.

6.

7.

J SOGe

11.

12.

1996;18:419-20

Crowley P. Elective induction of labour at <41 weeks gestation (revised 02 April 1992). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnancy and Childbirth Module. In: The Cochrane Pregnancy and Childbirth Database (database on disk and CDRom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London. Macer JA, Macer CL, Chan LS. Elective induction versus spontaneous labor: a retrospective study of complications and outcome. Am J Obstet Gynecol 1992;166(6 Pt 1):1690-6. SOCG Committee Opinion. Management of Post-term pregnancy. J SOGC 1994;16;4:1581-6. Liston R. Personal communication. Bakketeig LS, Hoffman JH, Harley EE. The tendency to repeat gestational age and birth weight in successive births. Am J Obstet GynecoI1979;135:1086-1103. Hannah ME, Hannah WJ, Hellmann J, Hewson S, Milner R, Willan A. Induction of labour as compared with serial antenatal monitoring in postterm pregnancy. A randomized controlled trial. The Canadian Multicentre Post-term Pregnancy Trial Group. N Engl J Med 1992;326(24):1587-92. Crowley P. Elective induction of labour at 41 + weeks gestation (revised 05 May 1994). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnanty and Childbirth Module. In: The Cochrane Pregnancy and Childbirth

JOURNAL SOGe

13.

14.

15.

16.

Database (database on disk and CD Rom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London. Huh C, Hannah ME, Hewson S, Hannah WJ, Willan A. Increased prostagiandin use and the results of the Canadian Multicentre Post-Term Pregnancy Trial (CMPpn. Proceedings of the SOGC Annual Meeting, Calgary, 1995. Bishop EH. Pelvis scoring for elective induction. Obstet Gynecol 1964;24:266-8. Keirse MJNC. Oxytocin for cervical ripening (revised 03 April 1992). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnancy and Childbirth Module. In: The Cochrane Pregnancy and Childbirth Database (database on disk and CDRom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London. Keirse MJNC. Endocervical PGE2 for cervical ripening (revised 03 April 1992). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnancy and Childbirth Module. In: The Cochrane Pregnancy and Childbirth Database (database on disk and CDRom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London. Keirse MJNC. Any prostaglandin/any route for clinical ripening (revised 03 April 1992). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnancy and Childbirth Module. In: The Cochrane Pregnancy and Childbirth Database (database on disk and CDRom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London. Chez RA. Cervical ripening and labor induction after previous cesarean delivery. Clin Obstet Gynecol 1995;38(2):287 -92. Keirse MJNC. Amniotomy plus early vs late oxytocin infusion for induction of labour (revised 03 April 1992). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnancy and Childbirth Module. In: The Cochrane Pregnancy and Childbirth Database (database on disk and CDRom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London. Keirse MJNC. Oral PGE2 vs intravenous oxytocin for induction of labour (revised 03 April 1992). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnancy and Childbirth Module. In: The Cochrane Pregnancy and Childbirth Database (database on disk and CDRom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London. Keirse MJNC. Vaginal prostaglandins vs oxytocin for induction of labour (revised 03 April 1992). In: Keirse MJNC, Renfrew MJ, Neilson JP, Crowther C (Eds). Pregnancy and Childbirth Module. In: The Cochrane Pregnancy and Childbirth Database (database on disk and CDRom). The Cochrane Collaboration; Issue 2, Oxford: Update Software; 1995. Available from BMJ Publishing Group, London.

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