Chapter 15 Induction and augmentation of labour

David T Y. Liu, Mentors: Sam Mukhopadhyay, Sabaratnam Arulkumaran

CHAPTER CONTANTS

Induction of labour as therapy 117

Indications for induction 117

Maternal 117

Fetal 117

Fetus and mother 118

Induction of labour as prophylaxis 118

Induction: general considerations 118

Contraindications to induction 118

Requirements before induction of labour 118

Induction of labour: process 119

Cervical ripening 119

Induction of labour 119

Bishop’s score of 4 or less 119

Bishop’s score between 4 and 7 (favourable cervix) 119

Induction of labour: artificial rupture of membranes 120

Technique for low ARM (forewater rupture) 120

Infusion of synthetic oxytocin (Syntocinon) 121

Risks of induction 121

Induction of labour: special situations 122

Previous caesarean section 122

Pre-labour rupture of membranes 123

For term fetus (36 completed weeks) 123

For 34 weeks’ gestation to term 123

Before 34 weeks’ of gestation 123

Breech presentation 123

Twin pregnancies 123

Intrauterine fetal death 123

Key points in induction of labour 124

Augmentation of labour 124

Augmentation before 3 cm cervical dilatation 124

Augmentation after 3 cm cervical dilatation 124

Induction of labour is a process for initiation of uterine activity to achieve vaginal delivery. Induction rates between 10% and 25% reflects current policies, referral patterns and sometimes women’s choice. Labour is initiated to benefit principally the mother, the fetus or both and as an elective prophylactic procedure. In the UK, women with uncomplicated pregnancies are offered induction of labour after 41 weeks.

INDUCTION OF LABOUR AS THERAPY

This is considered for the following reason:

• When it is safer for the woman not to continue pregnancy. Consider the woman’s preferences and priorities.

• When the fetus is less at risk if delivered or when both mother and fetus benefit by delivery. Induction must be the most appropriate mode of delivery.

Close surveillance in labour is mandatory when induction is carried out to address fetal or maternal compromise. If fetal distress develops or labour is not progressing well early resort to caesarean section is advised.

INDICATIONS FOR INDUCTION

Maternal

Medical or obstetric conditions not responding to treatment and which threaten the woman’s health, such as heart failure, severe pre-eclamptic toxaemia and deteriorating renal function or central nervous system disorders.

Fetal

Presence of progressive growth restriction, abnormality not compatible with life, or fetal death.

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Fetus and mother

Where induction of labour benefits both the mother and fetus, such as in poorly controlled diabetes, following rupture of fetal membranes or when chorio-amnionitis is evident. This indication is particularly pertinent in contemporary obstetric practice when women with medical conditions previously not considered suitable for pregnancy are now prepared to accept inherent risks to become mothers.

INDUCTION OF LABOUR AS PROPHYLAXIS

Induction of labour is also considered to anticipate potential complications. Examples are:

• Even in uncomplicated pregnancies, evidence suggests the fetus is best delivered by 2 weeks post term. Prophylactic induction reduces the incidence of caesarean section, instrumental delivery, fetal compromise during labour and perinatal mortality.

• To achieve better control after previous precipitated labour. (Labour less than 2 hours.)

• To avoid fetal demise in prior unexplained sudden death after fetal maturity.

• To avoid macrosomia and complications of shoulder dystocia especially in a diabetic woman.

• Occasionally induction is considered for logistic or psychosocial reasons such as difficult access to hospital because of distance.

INDUCTION: GENERAL CONSIDERATIONS

• Before formal induction, current practice suggests women should be offered membrane sweeping.

• Labour can subject both mother and fetus to stress. If there is significant compromise consider caesarean section as the preferred mode of delivery.

• When advice for induction of labour is declined close fetal and/or maternal surveillance is essential, e.g. scan for liquor volume, twice weekly cardiotocograph (CTG).

• When induction for fetal or maternal compromise fails deliver by caesarean section. When failure follows prophylactic indications, there is the option to reassess and repeat the process.

CONTRAINDICATIONS TO INDUCTION

Induction of labour should not be considered in the following situations:

• When vaginal delivery is not advised or possible, for example pelvic disproportion, placental praevia, cord presentation and in the presence of active infection such as genital herpes.

• Uterine contractions can cause uterine rupture after previous classic or inverted T uterine incision, after myomectomy or surgery which extends into the uterine cavity and where lower segment caesarean section is complicated by extension or infection. Review operation notes from previous caesarean sections. Palpate to exclude tenderness over previous lower segment caesarean section scar.

• Induction is contraindicated if labour threatens further compromise for mother and/or fetus.

Only proceed when the woman provides informed consent.

REQUIREMENTS BEFORE INDUCTION OF LABOUR

Review medical and obstetric history. Perform clinical examination to exclude contraindications for induction of labour. Ensure the woman and her partner are fully informed of the risk and benefits and consent to the intended programme. Provide written information.

Perform vaginal examination to assess adequacy of pelvis and determine cervical status. Cervical dilatation, cervical length, consistency, position and station of presenting part are combined into a score – Bishop’s score (Table 15.1), often modified to describe cervical status (Figure 15.1). A low score forewarns increased likelihood of induction failure and need for cervical preparation or ripening.

Table 15.1 Modified Bishop’s score

Figure 15.1 Cross-section of cervix to illustrate the degree of effacement.

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Cervical dilatation exerts twice the influence on successful induction compared with cervical consistency.

INDUCTION OF LABOUR: PROCESS

Cervical status governs choice for methods to induce labour. A low or unfavourable cervical score necessitates a ripening process for effacement and/or softening of the cervix to facilitate cervical dilatation. This is achieved by drugs, for example prostaglandins, which soften the cervix and produce uterine activity to draw up or create cervical effacement. Membrane sweeping releases prostaglandins and provides a biomechanical advantage to initiate or assist induction.

Cervical ripening

Pharmacological substances such as prostaglandins are prescribed to prepare or ripen the cervix. The current most clinically acceptable and effective is prostaglandin E₂ (PGE₂). PGE₂ given intravaginally as a pessary, as water soluble gel or more recently in the form of a slow-released hydrogel is associated with least systemic side effects. Vaginal pH, moisture, temperature, and infection can, however, all affect efficacy of the preparation. Do not use obstetric cream for vaginal examination if prostaglandins may be given. Where appropriate membrane sweep is returning as an acceptable procedure for uncomplicated pregnancies over 40 weeks. Both vaginal gel and vaginal tablets are equally effective and use is governed by cost.

Induction of labour

Auscultate fetal heart and perform CTG trace for 30 minutes prior to the induction process. Omit if induction is for fetal demise. If the trace is non-reassuring, discuss delivering by caesarean section.

Bishop’s score of 4 or less

Administer 2 mg prostaglandin gel into posterior fornix. Give another 1 mg in 6 hours if needed. Review by experienced obstetrician 6 hours after second dose. Uterine activity usually starts 1 hour after administration of prostaglandin gel. Pharmacological effect lasts up to 4 hours. Continuous CTG monitoring is essential. When there is no urgency let the woman rest overnight and recommence the programme in the morning. The maximum total dose of PGE₂used is 4 mg for primigravidae and 3 mg for multigravidae. Vaginal prostaglandin tablets are alternatives (3 mg PGE₂ vaginally and repeat once in 6 hours). With ruptured membranes consider vaginal prostaglandin or intravenous oxytocin.

Bishop’s score between 4 and 7 (favourable cervix)

In primigravidae start with 1 mg prostaglandin gel. Repeat after 6 hours if indicated. Again if labour is not established review by experienced obstetrician 6 hours after second dose. A maximum of 4 mg PGE₂ is advised.

In multigravidae start with 1 mg prostaglandin gel and repeat in 6 hours if required. Review 6 hours after last dose if labour is not established. A maximum of 3 mg is advised.

Uterine hypertonus or hyperstimulation may occur. Close fetal surveillance is essential. Monitor fetal heart rate for at least 60 minutes after inserting prostaglandins. Watch out for signs of uterine rupture when there is a lower segment caesarean section scar. If labour is not established by evening, return the woman to the ward if appropriate and repeat the programme in the morning. If labour ensues recommence fetal heart rate monitoring. Repeat tracing when mother is warded. If artificial rupture of membranes (ARM) is not possible after a course of prostaglandins review the situation with a senior obstetrician.

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Induction of labour: artificial rupture of membranes

With a Bishop’s score of 8 or more the cervix is often sufficiently dilated to allow access to the fetal membranes. Options are:

• membrane sweep

• ARM or amniotomy

• rupture of fetal membranes and start oxytocin (Syntocinon).

Surgical induction of labour can be achieved by passage of an instrument through the cervical os to artificially rupture the fetal membrane. Drainage of amniotic fluid reduces the size of the uterine cavity and promotes more effective contractions by improving the myometrial length tension ratio. Prostaglandins are also released from the decidua. Onset of labour usually follows amniotomy in 6–12 hours. This interval before onset of labour is shortened by simultaneous use of intravenous infusion of an oxytocic such as Syntocinon.

Technique for low ARM (forewater rupture)

Make sure the woman and her partner give consent (verbal or written) and understand the reasons and steps for the procedure.

Place mother in the lithotomy position. Use sterile drapes and an aseptic technique. The fetal membranes in front of the presenting part can be ruptured using forceps such as Kocher’s forceps or various designs of amniohooks (Figure 15.2).

Figure 15.2 Instruments for low ARM.

If placenta praevia has not been excluded by ultrasound examination palpate the vaginal fornices carefully. Suspect placenta praevia if a thick spongy sensation is felt between the fornices and presenting part of the fetus (Figure 15.3). Insert a finger through the cervical os. Palpate the membranes through the internal os for a distance of 2 cm to exclude pulsating vessels associated with vasa praevia or cord presentation.

Figure 15.3 Palpation of vaginal fornices to exclude placenta praevia.

When amniotomy is not contraindicated insert a second finger (index and middle fingers are used). Guide the forceps between the fingers to the membranes (Figure 15.4). The membranes are picked up by the forceps and ruptured by wiping the index finger over the tip of the forceps. This technique allows good control of the amount of tear and the rate of escape of amniotic fluid. Record quantity and colour of liquor (blood stained, meconium or clear).

Figure 15.4 Technique for low ARM with Kocher’s forceps.

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Alternatively introduce an amniohook through the cervix. This is guided to a safe area of the presenting part of the fetus (for example, away from the fetal face). Approximate amniohook to the membrane by the index finger. The hook is withdrawn to tear the membranes. An advantage of this option is the need for less cervical dilatation, but the size of the tear is less predictable.

Infusion of synthetic oxytocin (Syntocinon)

Points to note with Syntocinon usage are:

• Myometrial sensitivity to oxytocin increases throughout pregnancy.

• Oxytocin increases both frequency, duration and amplitude of contractions. Use minimal dose which produces adequate uterine contractions. Maximum recommended dose is 20 mU/min.

• Prior treatment with prostaglandins potentiate action of oxytocin. Do not use oxytocin before 6 hours after last dose of PGE₂.

• Oxytocin at 30 IU in 500 ml of normal saline will give 1 mU/min if run at 1 ml/h.

• Intravenous oxytocin can be titrated to give better control of uterine contractions. Commence infusion using regulated drip set to deliver 2 mU/min and escalate dose at 2 mU/min every 30 minutes until contractions lasting 40 seconds recur every 4–5 times in 10 minutes. The dosage schedule recommended in the National Institute for Health and Clinical Excellence (NICE) guidelines is indicated in Table 15.2. Most women however, achieved adequate uterine contractions with 12 mU/min of Syntocinon. Once labour is established, maintain the same dose until delivery unless hyperstimulation warrants reduction in the dosage. Some women will continue labour when the dose is reduced to 8 mU/min. Infusion pumps should be used to control accurate delivery of the oxytocin infusion (Figure 15.5).

• After prolonged use of oxytocin maintain infusion for 1 hour after delivery to minimise the possibility of atonic postpartum haemorrhage.

• Side effects of Syntocinon usage include: uterine hyperstimulation, water retention due to an anti-diuretic effect once the dosage exceeds 16 mU/min and maternal and fetal hyponatraemia. Water toxicity and hyponatraemia can cause maternal headache, nausea, psychosis and convulsions. Fetal adverse effects include lethargy, feeding difficulties, apnoea, cyanotic spells, respiratory distress and convulsions. Neonatal hyperbilirubinaemia has been described after oxytocin infusion.

• Start Syntocinon once membranes are ruptured particularly in the primigravida. Close monitoring of both mother and fetus is mandatory.

Table 15.2 Oxytocin regimen for induction of labour (NICE 2001)

Figure 15.5 An infusion pump.

Doses in bold italics are quantities above those referred to in the summary of product characteristics of 20 mU/min (Table 15.2).

Figure 15.6 presents an algorithm for induction of labour depending on the presence or absence of complications in pregnancy.

Figure 15.6 Algorithm for induction of labour (NICE 2001).

RISKS OF INDUCTION

• Failed induction

This describes the situation when effective uterine activity is not established or maintained. Failure is less likely for gestations near term or when the Bishop’s score is high. When membranes are ruptured there is the risk of infection. Deliver by caesarean section if there is fetal or maternal compromise.

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• Intrauterine infection

Once membranes rupture intrauterine and fetal infection is more likely. Some women such as those with diabetes are more susceptible. Where possible exclude active vaginal infection such as cervical herpes and presence of Group B streptococcus. Once membranes rupture monitor maternal pulse and fetal heart rate and maternal temperature. Aim to achieve delivery within 24 hours.

• Cord prolapse

Incidence of cord prolapse is 0.1–0.5% following membrane rupture. Exclude cord presentation before rupturing membranes. This complication is more likely when the fetal presenting part is not well applied to the cervix or when there is polyhydramnios.

• Uterine hyperstimulation

Pharmacological agents used to stimulate uterine activity can lead to excessive amplitude and frequency of contractions. Once the contraction frequency exceeds 5 per 10 minutes uterine activity becomes less efficient. Hyperstimulation follows use of high concentrations of oxytocics or where a woman is particularly sensitive to the drug. Hyperstimulation causes fetal hypoxia and threat of uterine rupture particularly in the grand multipara or in women with previous caesarean section scars. β-sympathomimetics such as ritodrine (50 μg to maximum of 350 μg per minute) or terbutaline, 250 μg subcutaneously or in 5 ml saline can be given intravenously to overcome hyperstimulation (20 μg/min should not be exceeded).

INDUCTION OF LABOUR: SPECIAL SITUATIONS

Previous caesarean section

• Induction of labour is contraindicated in a uterus with a classical, inverted ‘T’ or complex extended scar. This statement also applies to situations in which the uterine cavity was entered such as during myomectomy, when uterine infection caused poor uterine wound healing and after two previous caesarean sections.

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• For high Bishop’s scores with ruptured membranes titrate uterine activity with intravenous Syntocinon.

• For low Bishop’s scores administer 1 mg prostaglandin E₂(PGE₂) vaginally_.The risk of scar dehiscence or rupture varies between 0.7% and 2.2%. Repeat doses of PGE₂must be balanced against this risk.

• Watch out for signs of scar rupture and fetal distress.

Pre-labour rupture of membranes

• Membrane rupture carries risk of cord prolapse and intrauterine infection. Infective morbidity increases after 48 hours. More than 75% of women, however, labour spontaneously within 24 hours of membrane rupture.

• Take careful history, perform clinical examination to determine presence or absence of uterine activity or uterine tenderness. Confirm the presence of membrane rupture and exclude cord prolapse. Commence CTG monitoring.

For term fetus (36 completed weeks)

Induce labour immediately if there is threat or evidence of maternal or fetal infection. Deliver by caesarean section if CTG suggests evidence of fetal compromise.

If there is no risk of complication or fetal or maternal compromise discuss options with the woman. Conservative management for 24 hours to await spontaneous onset of labour is acceptable. Induce labour after 24 hours of ruptured membranes.

For 34 weeks’ gestation to term

Allow pregnancy to continue. When obstetric risk is present such as infection or fetal compromise induce labour or deliver by caesarean section where appropriate.

If conservative management is acceptable take cervical swabs. Transfer to antenatal ward and commence 4 hourly recording of maternal pulse rate and temperature. Check abdomen for tenderness at the same time. Perform twice daily fetal CTG recordings and weekly ultrasound scan of the fetus. Deliver at 37 weeks or if fetal compromise becomes evident.

Before 34 weeks’ of gestation

In the absence of contraindications such as infection give two doses of 12 mg dexamethasone at 12 hourly intervals. Dexamethasone can cause a transient rise in white cell count for 24–36 hours. The fetal heart rate change is difficult to interpret but fetal tachycardia is a useful guide for infection. Give appropriate antibiotics for pathogens. Deliver if chorioamnionitis is evident. Consider caesarean section if there is fetal risk.

Adopt the same criteria for induction as described above. Vaginal prostaglandin is not contraindicated.

Breech presentation

Contemporary practice advises attempts at external cephalic version when there is no contraindication and if this is unsuccessful deliver by caesarean section. The woman’s informed opinion must be considered. Current evidence recommends that caesarean section for breech presentation is the safest approach.

Twin pregnancies

In the absence of obstetric complications induction of labour by amniotomy or use of prostaglandin is not contraindicated. Requirements for twin delivery must be satisfied. The first twin should be in cephalic presentation. Breech presentation of the first twin suggests the need for delivery by caesarean section.

Intrauterine fetal death

The main risks associated with intrauterine fetal death are infection, and if the dead fetus is retained more than four weeks coagulopathy may develop.

• Confirm fetal death by ultrasound scan.

• Convey the news with empathy and offer possible explanation for the death. Consult with all involved to arrange a mutually acceptable time for induction of labour. Immediate induction of labour after confirmation of intrauterine death may not be the most helpful psychological approach. Onset of coagulopathy can vary. Check platelet count and perform clotting screen.

• Administer prostaglandins as described above. Recently misoprostol, a cost-effective option has also been used.

• In very early pregnancies (before 24 weeks of gestation) extraamniotic prostaglandin delivered by placement of a size 12–14 Foley catheter through the cervix is an option. The balloon is inflated with 20–40 ml of saline to keep the catheter in place. An infusion pump is used to deliver PGE₂ 10 mg/ml at a rate of 0.5 ml/h. This can be increased by 0.5 ml hourly to a maximum dose of 3.0 ml/h. Augment with oxytocin (Syntocinon) if delivery is not achieved within 24 hours. Misoprostol 500 μg every 4 hours is the current alternative. Cervical laceration and uterine rupture are recognised complications. Examine the woman carefully and observe closely for 6 hours after delivery.

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• When induction of labour is contraindicated (rarely) or carries substantial risk deliver by hysterotomy or caesarean section.

KEY POINTS IN INDUCTION OF LABOUR

• Make sure the woman and her partner are aware and accept the reasons, process and risk of induction.

• Decision and assessment for induction of labour must be made by an experienced obstetrician.

• Deliver by caesarean section instead of induction for severe maternal or fetal compromise.

• Deliver by caesarean section when induction for maternal and fetal compromise is unsuccessful.

• Oxytocin by intravenous infusion allows good control of uterine activity. Use the minimum dose which provides adequate uterine contractions.

• The pharmacological effect of oxytocin is potentiated after administration of prostaglandin.

• Once membranes are ruptured aim to deliver within 24 hours to reduce risk of intrauterine infection.

• Close maternal and fetal surveillance is mandatory.

AUGMENTATION OF LABOUR

This process describes enhancement of uterine contractions when progress of labour is slow. Before augmentation exclude malpresentation, gross disproportion and fetal or maternal compromise.

Decision to augment labour must follow assessment of situation by experienced obstetrician. This decision must be acceptable to the woman. Aim to achieve adequate contractions (frequency of four to five contractions per 10 minutes, each contraction lasting 40–60 seconds). Contractions should produce cervical dilatation and descent of the presenting part. A wide range of uterine activity can produce cervical dilatation averaging 1 cm/h.

Augmentation, like induction of labour, must be conducted with due care. This care includes nursing support, pain relief and close surveillance.

Augmentation before 3 cm cervical dilatation

In the latent phase of labour, augmentation is advised after 8 hours of painful contractions occurring at a frequency of 2 every 10 minutes if there is slow progress (World Health Organization (WHO) 1994). Exclude contraindications to labour.

Augmentation after 3 cm cervical dilatation

This is considered when cervical dilatation drifts 2–3 hours to the right of the alert line of the normal partogram (WHO 1994). Exclude contraindications to further labour. Rupture fetal membranes if these are still intact. The same Syntocinon regimen for induction of labour is used. Labour progress is measured both in terms of cervical dilatation and descent of the fetal head. Cervical dilatation without descent of the fetal head forewarns of possible disproportion.

Close surveillance is mandatory. If fetal distress develops or little change is detected after 4 hours of adequate contractions consider delivery by caesarean section. In the absence of contraindications 6–8 hours of oxytocin can result in optimal outcome.

Obstructed labour in primigravidae leads to incoordinate labour or cessation of uterine activity. In multigravidae the uterus attempts to overcome the obstruction by increasing frequency and intensity of contractions with resultant tetanic uterine activity and risk of uterine rupture.

References

National Institute of Clinical Excellence. Induction of labour. London: Clinical Guideline D. NICE, 2001.

World Health Organization. Maternal Health and Safe Motherhood Programme. World Health Organization Partograph in management of labour. Lancet. 1994;343:1399-1404.

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