Induction of labour (IOL) is the artificial commencement and stimulation of labour and involves the ripening of the cervix, artificial rupture of the membranes (ARM) and stimulation of uterine contractions. It is indicated when delivery of the baby before spontaneous labour occurs is in the best interests of the mother or fetus, or both.
Augmentation of labour is used where the normal progress of labour is slower than expected or when there is rupture of membranes but no uterine contraction.
Induction of labour
The indications for IOL are shown in Table 63.1. Certain factors (e.g. previous caesarean section or breech pregnancy) may increase the risk of complications of IOL (see below), so it should only be offered by a senior obstetrician and after the risks and benefits have been clearly discussed.
Before an induction of labour is offered, a membrane sweep may be performed; this is viewed as an adjunct that increases the chance of spontaneous labour by stimulating prostaglandin release. Once the decision to induce labour has been made, the ease of induction is usually assessed by using the Bishop score, based on the result of pelvic examination. This takes into account the station of the presenting part and cervical features (dilatation, effacement/length, position and consistency). A Bishop score above 8 suggests the cervix is ripe and spontaneous labour or response to induction is likely, whereas a low score indicates that the cervix is unfavourable and spontaneous labour is unlikely. In the latter case, the cervix may be ripened by vaginal dinoprostone (PGE2), which may be repeated at intervals of 12-24 hours depending on the change in the Bishop score. This process may take more than 48 hours. Misoprostol and mifepristone have also been used to induce labour, but currently are usually used only in women who have an intrauterine fetal death.
Table 63.1 Indications for induction of labour
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Fetal reasons |
Prolonged pregnancy Fetal growth restriction Multiple pregnancy Unstable lie Infection Rhesus disease Lethal fetal abnormality Intrauterine death |
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Maternal reasons |
Pregnancy-induced hypertension Essential hypertension Other maternal disease, e.g. renal, malignant Antepartum haemorrhage Poor obstetric history, e.g. previous stillbirth |
Surgical IOL (ARM) is performed if the cervix is favourable or following cervical ripening with prostaglandins, or if there are clinical reasons not to use PGE2 such as a uterine scar, severe fetal growth restriction or medical reasons such as asthma. This stimulates labour and allows the colour of the liquor to be assessed and a fetal scalp clip electrode to be applied to monitor the fetal heart, both of which give information about the wellbeing of the fetus. Balloon catheters are not used routinely for IOL but may be used for women with a uterine scar.
Oxytocics are usually an integral part of the management of IOL, and therapy is normally commenced after ARM has been performed.
Augmentation of labour
Augmentation of labour is used when labour is not proceeding at the standard rate (see Chapter 19, Normal labour) or when there has been premature rupture of membranes without signs of labour after 12-24 hours. It is usually done by ARM (if intact) and/or oxytocics.
Problems and special considerations
The most common complications of IOL are:
1. Prolapse of the cord.
2. Abruption of the placenta.
3. Acute fetal compromise - particularly when ARM is performed in the presence of polyhydramnios.
4. Hyperstimulation of uterine contractions, causing acute fetal compromise. A PGE2 pessary may need to be removed or oxytocin stopped and a tocolytic such as terbutaline (250 μg subcutaneously) or glyceryl trinitrate (50 µg intravenous boluses or 200-400 μg sublingually) administered.
5. Postpartum haemorrhage associated with uterine atony.
Complications of augmentation are as above. In addition, there is an increased risk of infection if the membranes have been ruptured for some time.
IOL is often prolonged, and may be particularly tiring and painful, as it increases the strength of the contractions. There fore epidural analgesia should be discussed as part of the labour management, as well as the above complications. Contractions augmented by oxytocic drugs are also more intense and frequent, and therefore appear to be more painful. There may also be maternal or fetal reasons for the advisability of epidural analgesia, for example pregnancy-induced hypertension.
Induction of labour may not be successful, and since there has been a commitment to deliver the baby these women may need to be delivered by caesarean section.
IOL is often associated with a high-risk pregnancy.
There is an increased risk of precipitous labour and instrumental delivery.
Key points
• Induction and augmentation of labour may employ pharmacological or surgical methods.
• There may be an increased need for anaesthetic involvement, secondary to increased pain, operative delivery or complications.
Further reading
Mozurkewich EL, Chilimigras JL, Berman DR, et al. Methods of induction of labour: a systematic review. BMC Pregnancy Childbirth 2011; 11: 84.
Mozurkewich E, Chilimigras J, Koepke E, Keeton K, King VJ. Indications for induction of labour: a best-evidence review. BJOG 2009; 116: 626-36.
National Institute for Health and Care Excellence. Inducing Labour. Clinical Guideline 70. London: NICE, 2008. www.nice.org.uk/guidance/CG70 (accessed December 2018).