Chapter 62 Induction of labour and post-term pregnancy
Induction of labour
Induction of labour is when labour is artificially initiated before spontaneous onset occurs. It has been described as being ‘one of the most drastic ways of intervening in the natural process of pregnancy and childbirth’ (Enkin et al 2000:375). It may also affect the birth experience itself, as it can be less efficient and more painful than spontaneous labour. In addition, it increases the risk of further medical intervention.
In 2005–06 in NHS units in England, the incidence was 20.2%, with less than two-thirds of women delivering spontaneously. Where delivery was induced by drugs, whether or not surgical induction was also attempted, about 15% had instrumental deliveries and 23% emergency caesareans (Richardson & Mmata 2007). Despite this, it is common practice in modern maternity units in the UK.
Indications for induction of labour mainly relate to increased risk of fetal and/or maternal compromise if delivery is delayed. The risks and benefits and any possible consequences should be carefully considered and discussed with the woman prior to its commencement. Induction of labour should only be contemplated when a vaginal birth is feasible (National Collaborating Centres for Women’s and Children’s Health [NCC-WCH] 2008a).
Maternal indications
Hypertension
Hypertensive disorders are one of the principal indications for induction, and timely intervention may become necessary to avoid serious maternal morbidity and perinatal compromise (Ch. 56).
Other medical conditions
Pre-existing renal, cardiac or other medical disease can deteriorate as pregnancy progresses, and induction may be indicated in some of these pregnancies (Ch. 55).
Prelabour rupture of the membranes
Preterm, prelabour rupture of the membranes (PPROM) occurs before the onset of regular uterine contractions and before 37 weeks (Ch. 60). The two main risks of PPROM are preterm birth and infectious morbidity due to ascending intrauterine infection. PPROM occurs in only 2% of births but is responsible for around 40% of all preterm births (Douvas et al 1984, Maxwell 1993, Merenstein & Weisman 1996). Unless there are additional obstetric indications, such as infection or fetal compromise, induction of labour is not indicated before 34 weeks (NCC-WCH 2008a).
At 37 weeks or after, induction is known as prelabour rupture of membranes at term (PROM). PROM occurs in 8% of all term pregnancies (Dare et al 2006). Complications include: maternal and neonatal infection, prolapsed cord, increased risk of caesarean section and a low 5-minute Apgar score. Induction of labour may reduce the numbers of babies admitted to neonatal units and increase maternal satisfaction (Dare et al 2006).
Women with PROM should be offered either immediate induction or expectant management. National guidance recommends that induction of labour is appropriate 24 hours after PROM (NCC-WCH 2007).
Maternal request
Induction of labour may be requested by women for social or emotional reasons. For example, partner being posted abroad with armed services or increased anxiety or stress which may or may not be directly associated with the pregnancy. Induction should not be routinely offered, but in exceptional circumstances it may be considered at or after 40 weeks (NCC-WCH 2008a).
Poor obstetric history
Induction is sometimes undertaken to alleviate the anxiety and stress associated with subsequent pregnancies following previous adverse outcome, although it may have no clinical relevance to the current pregnancy. However, it is not indicated where there is a history of precipitate labour (NCC-WCH 2008a).
Fetal indications
Fetal growth restriction
Induction may be indicated if there is evidence of diminished fetal wellbeing caused by uteroplacental insufficiency, which is often characterized by intrauterine growth restriction, abnormal fetal movements and/or abnormal fetal umbilical blood flow detected by Doppler ultrasound. However, induction is not indicated if the fetus is severely growth restricted (NCC-WCH 2008a). As the fetus is likely to become severely compromised in labour, a caesarean section is the preferred method of elective delivery.
Macrosomia
Macrosomia not associated with diabetes has been an indication to induce labour in order to avoid difficult delivery, shoulder dystocia and their consequences. However, accurate diagnosis of estimated fetal weight remains problematic. The evidence suggests that there is little benefit in induction for suspected fetal macrosomia (Irion & Boulvain 1998).
Fetal death
When fetal death has occurred with no other apparent obstetric or medical complications, there are no overwhelming benefits or risks of induction of labour over expectant care. The woman should be allowed to choose the best option for her and her family. If, however, there is evidence of ruptured membranes, infection or bleeding, immediate induction is indicated (NCC-WCH 2008a).
Rhesus isoimmunization
Induction of labour is an optional management for established isoimmunization when the fetus is considered sufficiently mature, is not too severely affected and can be effectively treated after birth (Enkin et al 2000).
Contraindications
Placenta praevia
There is almost no indication for vaginal birth when the fetus has reached a viable age, because of the risks of maternal and fetal haemorrhage, cord accidents and malpresentations (Enkin et al 2000).
Cephalopelvic disproportion
Proven cephalopelvic disproportion may be a contraindication for induction of labour. However, it is rarely possible to make an accurate diagnosis except in cases of known altered anatomy, for example, severe contracture or pelvic fractures. The literature shows that successful vaginal birth occurs in over 50% of caesarean sections for disproportion, dystocia or failure to progress (Paterson & Saunders 1991, Rosen & Dickinson 1990, Rosen et al 1991).
Oblique or transverse lie in labour
These are absolute contraindications because of the risks of cord prolapse and obstruction.
Methods
Induction is usually timed for when it will be most successful, that is, near the onset of spontaneous labour. But there are situations when it will be necessary to intervene before term to reduce the risk of fetal and/or maternal compromise. Corticosteroids should be administered to a woman who will deliver before 36 weeks to promote fetal pulmonary maturity and thereby reduce the risk of mortality, respiratory distress syndrome and intraventricular haemorrhage in preterm infants (RCOG 2006).
Cervical ripening
The success of induction and subsequent length of labour are primarily determined by the state of the cervix at the time of induction. An ‘unripe’ or unfavourable cervix fails to dilate adequately and results in high failure rates (Enkin et al 2000). Prior to induction, the state of the cervix is assessed using a score based on that originally proposed by Bishop (1964). Five qualities are rated (see Table 62.1):
When the total score is greater than 8, the cervix is said to be favourable (NCC-WCH 2008a).
Risks of cervical ripening
Intrauterine infection is mainly associated with invasive techniques, such as mechanical devices and extra-amniotic procedures. Iatrogenic uterine hyperstimulation and fetal heart rate abnormalities during the cervical ripening period can lead to emergency caesarean section with its associated morbidity (Ch. 61). Failure to produce any significant change in cervical favourability may lead to delivery by caesarean. The consequences of initiating any procedure with its sequelae should always be considered and discussed in full with the woman prior to its commencement.
Membranes sweeping
Sweeping or stripping the membranes from the lower uterine segment at term has traditionally been used to induce labour in the hope that amniotomy or oxytocic drugs may be avoided. It involves placing a finger inside the cervix and making a circular, sweeping action to separate the membranes from the cervix. The theory behind this method is that localized prostaglandin production is increased (Mitchell et al 1977).
Boulvain and colleagues (2005) found that membrane sweeping reduced the time from intervention to spontaneous onset of labour or birth by a mean of 3 days. It also reduced the incidence of prolonged pregnancy if performed from 38 to 40 weeks and thereby reduced the need for formal induction of labour. However, the reviewers felt there is little justification to undertake the procedure routinely prior to 40 weeks’ gestation.
Sweeping the membranes was not associated with an increase in maternal or neonatal infection or premature rupture of the membranes, but one trial (Boulvain et al 1998) reported increased maternal discomfort during and after the procedure with both vaginal bleeding and painful contractions not leading to the onset of labour during the 24 hours following the intervention.
Prostaglandin
Prostaglandin (PGE2) has been used since the late 1960s for cervical ripening and induction of labour in a variety of different preparations and doses. In the UK, vaginal prostaglandin is one of the most commonly used induction agents. It is more likely than either placebo or no treatment to start labour and to avoid the need for induction with oxytocin (Enkin et al 2000). Vaginal PGE2 is associated with improved cervical status, reduced need for oxytocin augmentation and meconium staining. With a favourable cervix, it improves the successful vaginal delivery rate within 24 hours (NCC-WCH 2008a).
Vaginal PGE2 in tablet or gel preparations, is the recommended method of induction of labour irrespective of cervical favourability or membrane status. Controlled-release pessary may be more appropriate when the cervix is unfavourable, to reduce the need for repeated doses of single-dose preparations (NCC-WCH 2008a). The recommended cycle for single vaginal dose preparations is one dose followed by a second dose 6 hours later if not in established labour (two doses maximum).
The associated complications of prostaglandin administration include:
Oxytocin
Uterine rupture is a rare but life-threatening consequence of uterine hypercontractility. The suggested management for uterine hyperstimulation is to stop the oxytocin, as the short half-life of the drug will reduce the degree of fetal compromise, dependent upon fetal reserve. Tocolytics are also recommended (NCC-WCH 2008a).
There is also evidence that the incidence of neonatal hyperbilirubinaemia is increased with the use of oxytocin (Enkin et al 2000).
