‘The spontaneous onset of labour is a robust and effective mechanism which is preceded by the maturation of several fetal systems, and should be given every opportunity to operate on its own. We should only induce labour when we are sure that we can do better.’ ALEC TURNBULL, 1976
The first reliable technique to be used widely in obstetric practice for induction of labour was amniotomy or artificial rupture of the membranes. It first entered the medical literature in 1756 when Thomas Denman (1733–1815) of the Middlesex Hospital of London wrote extolling its virtues. As a result it became known within Europe as the ‘English method’.
Another mechanical method was devised in 1861 by Robert Barnes (1817–1907) of London, using a hydrostatic bag placed through the cervix and filled with water. A similar approach was later taken by Camille Champetier de Ribes (1848–1935) in Paris and by James Voorhees (1869–1929) in New York which all preceded the understanding that the modus operandi was local release of prostaglandins.
However, it was not until oxytocin was made available for clinical application that any degree of reliability in labour induction could be achieved. Sir Henry Dale (1875–1968) made the first observation that posterior pituitary extract caused uterine contractions. He gave samples to the obstetrician William Blair Bell (1871–1936) who began to use it for induction of labour. Nevertheless, because the crude extracts of the posterior pituitary were of variable purity and potency, and because these were initially given as intramuscular injections with a poor degree of control, it was hardly surprising that there were instances of calamitous hyperstimulation of the uterus. It was not until the latter half of the 20th century that reliable preparations of oxytocin became available following its chemical characterization as an octapeptide and its synthetic elaboration. There followed a period of controversy during which Geoffrey Theobald advocated a dilute intravenous infusion of oxytocin as a ‘physiological drip’, motivated by the desire to maximize the safety of the drug, but actually reducing its potency and reliability. It was not until the late 1960s that Alec Turnbull and Anne Anderson advocated the more pharmacologically sound approach of oxytocin ‘titration’ whereby the dose rate was steadily increased until the uterus responded by contracting effectively, at which point the dose rate was held steady. A significant new development in the practice of labour induction was the clinical availability of prostaglandins. First recognized in the 1930s, it took more than 30 years to reach the point of clinical application, largely as a result of work by Sune Bergstrom and his colleagues at the Karolinska Institute in Stockholm. By 1975 it was clear that prostaglandins added an extra dimension to induction of labour, particularly since they not only provoked uterine contractions but also had a positive effect on cervical ripening. As with oxytocin, a variety of different routes were explored before it was recognized that local delivery required a lower dose and greatly reduced unpleasant side effects. Simply introducing PGE 2 into the vagina has become the route of choice.
More than a century after Barnes, Champetier de Ribes and Voorhees pioneered mechanical methods of induction of labour, things have come full circle, with increasing evidence that using a Foley catheter or cervical ripening balloon is an effective way of inducing labour, with lower rates of hyperstimulation than prostaglandin.
Indications for Induction of Labour
Induction of labour is one of the most commonly performed obstetric interventions, with more than 20% of mothers in developed countries having their labour induced. It is offered when it is believed that the outcome for mother or baby, or both, is better served by delivery than by allowing the pregnancy to continue. Each pregnancy should be assessed in respect of the ‘obstetric balance’ ( Fig 8-1 ). The perceptive clinician will immediately recognize that such a view is unduly simple for two reasons. First, the risks of the process of induction of labour must be considered. There is no virtue in intervening by inducing labour to avoid a perceived risk if the nature of the labour which results risks greater jeopardy for either party. Second, an intervention which may be in the interests of one partner in the pregnancy may counter the interests of the other. For instance, induction of labour in a mother with pre-eclampsia may be beneficial in reducing the risks which she faces, while at the same time exposing the offspring to the risks of prematurity.
When considering whether to offer induction of labour or not, each pregnancy must be considered individually, taking account of the risks and benefits to mother and baby deriving from specific complications and the risks of induction of labour. Importantly, the mother’s preferences, values and perceptions of risk should be considered. Common indications for induction of labour are outlined below. Figure 8-2 outlines a paradigm to be followed when the question of interruption of pregnancy arises.
Prolonged Pregnancy
It is estimated that up to 10% of pregnancies continue beyond 294 days (42 weeks). Both mother and fetus are at increased risk when the pregnancy continues beyond term, with the risk of neonatal and postneonatal death significantly increased after 41 weeks.
A Cochrane systematic review and meta-analysis of trials of induction of labour at or beyond term (37 weeks and beyond) found that compared with expectant management, a policy of labour induction was associated with fewer perinatal deaths (risk ratio 0.31, 95% confidence interval (CI) 0.12 to 0.88) and less meconium aspiration in babies (risk ratio 0.50, 95% CI 0.34 to 0.73).
Although it is commonly perceived that induction of labour can increase operative deliveries including caesarean section, it is important to note that there were actually fewer caesarean sections with induction of labour compared with expectant management (risk ratio 0.89, 95% CI 0.81 to 0.97).
Pre-Eclampsia and Gestational Hypertension
Hypertensive disorders in pregnancy are associated with increased maternal and neonatal morbidity. In cases of severe pre-eclampsia, ending the pregnancy is the treatment of choice. In milder cases the risks and benefits of induction of labour are less clear cut. A randomized controlled trial of induction of labour (n=377) or expectant monitoring (n=379) for women with mild gestational hypertension or pre-eclampsia at 36 weeks or greater gestation found that fewer women randomized to induction of labour developed poor maternal outcome (relative risk 0.71, 95% CI 0.59−0.86, p < 0.0001). Neonates born to mothers randomized to induction of labour were lighter, but no differences in neonatal morbidity were seen. In cases of mild pre-eclampsia and gestational hypertension prior to 36 weeks’ gestation, the potential risks of iatrogenic prematurity associated with induction of labour are higher and must be balanced against the risks of continuing the pregnancy.
Maternal Diabetes
Women with diabetes have higher risk of pregnancy complications including intrauterine death, macrosomia and birth trauma. There has been only one randomized-controlled trial of induction of labour in diabetic pregnancies, comparing induction of labour at 38 weeks’ gestation to expectant management to 42 weeks. There was no difference in caesarean section rates between groups (relative risk 0.81, 95% confidence interval (CI) 0.52−1.26), but the risk of macrosomia was lower with induction of labour (relative risk 0.56, 95% CI 0.32−0.98). The UK National Institute for Clinical Excellence (NICE) has reviewed the evidence for management of diabetic pregnancy and recommends that induction of labour (or caesarean section if indicated) is offered at 38 weeks’ gestation to women with diabetes requiring insulin (NICE guideline Diabetes in Pregnancy (CG63) ).
Twins and Multiple Pregnancy
Epidemiological data suggest that in twin pregnancies ‘term’ may be earlier than in singletons, and morbidity and mortality in twin pregnancies are the lowest in association with delivery at 36–38 weeks’ gestation. Current NICE guidelines endorse elective delivery around 37 weeks for dichorionic twins and 36 weeks for monochorionic twins. There is not clear evidence from randomized trials that induction of labour improves outcomes for twins, but a recent randomized trial of elective delivery around 37 weeks’ gestation compared to expectant management, did suggest that neonatal morbidity may be reduced, principally through a reduction in birth weight < 3rd centile. The trial thus supports observational data, and current national recommendations that women with uncomplicated twin pregnancy should be offered delivery around 37 weeks to optimize infant outcome.
Preterm Prelabour Rupture of the Membranes
When the fetal membranes rupture before the onset of labour the risks of intrauterine infection leading to neonatal and/or maternal sepsis with continuing pregnancy must be weighed against the risks of prematurity resulting from immediate delivery. At gestations remote from term the risks of prematurity are considerable, and expectant management with monitoring of maternal and fetal wellbeing appears to be preferable unless there are clear signs of impending maternal or fetal compromise. The results of the PPROMEXIL trial suggest that even when prelabour rupture of membranes occurs closer to term expediting delivery by inducing labour does not confer any benefits. The paper, which also includes a meta-analysis of similar trials, found that overall rates of neonatal sepsis were low, and there was no reduction in risk of neonatal sepsis (relative risk of 1.06 (95% CI 0.64 to 1.76) ) or caesarean section (relative risk 1.27 (95% CI 0.98 to 1.65) ) with induction of labour compared to expectant management. It supports a ‘watch and wait’ approach, unless there is clear evidence of infection or other concerns for maternal or fetal wellbeing.
Intrauterine Growth Restriction
When there is an inadequate oxygen or nutrient supply to the fetus, there are progressive alterations in the growth, metabolic, cardiovascular and behavioural parameters of the fetus, which represent increasing hypoxaemia and acidosis. When such fetal compromise is suspected, immediate delivery may decrease the risk of damage due to intrauterine hypoxia. However, it may also increase the risks of prematurity. The Growth Restriction Intervention (GRIT) trial aimed to assess the effects of immediate delivery and delayed delivery of the preterm fetus (24−36 weeks) with suspected growth restriction. Overall there were no differences in neurodevelopment impairment or death and disability at or after 2 years, but more babies in the immediate delivery group were ventilated for more than 24 hours (relative risk 1.54, 95% CI 1.20 to 1.97), and more women in the immediate delivery group had caesarean delivery (relative risk 1.15, 95% CI 1.07 to 1.24). A Cochrane review of immediate or deferred delivery for the preterm fetus with suspected fetal compromise concluded that more research is needed, but where there is uncertainty whether or not to deliver, deferring delivery until test results worsen or increasing gestation favours delivery may improve the outcomes for mother and baby.
There is also no clear evidence of benefit to induction of labour in cases of growth restriction identified at term. A randomized trial (DIGITAT) found no important differences in adverse outcomes between induction of labour and expectant monitoring in women with growth restriction greater than 36 weeks. The authors concluded that women who are keen on non-intervention can safely choose expectant management with intensive maternal and fetal monitoring; however, it is rational to choose induction to prevent possible neonatal morbidity and stillbirth.
Elective Induction of Labour
Elective induction of labour (i.e. in the absence of a recognized medical complication) may be offered for maternal or physician preference or social and geographical considerations (e.g. availability of partner, distance from hospital). A population based cohort study found that perinatal mortality and maternal complications were lower and vaginal delivery rates higher in association with elective induction of labour around term, when compared to expectant management. However, induction of labour was associated with higher rates of neonatal unit admission. Other studies have found a reduction in caesarean delivery associated with elective induction of labour when compared to expectant management. Although these findings are from observational studies, they can be used to help counsel women about management options for delivery.
Methods of Induction
It is recognized that some labours can be induced with ease while others may prove extremely resistant to induction. It is likely that the biggest single factor is the proximity to the spontaneous onset of labour. Because the transition from the state of pregnancy maintenance to established labour is a gradual one (see Chapter 1 ), it is obvious that if a particular woman is programmed to be in labour tomorrow, labour induction today is likely to be simple. In contrast if, even at or beyond term, spontaneous labour remains a distant prospect then induction is almost inevitably fraught with difficulty. The most useful predictor of this is the degree of cervical ripening. Indeed, the original study on which Bishop based his cervical scoring system correlated the score to the interval before spontaneous labour began. A high score presaged a short delay before the onset of labour; a low score indicated that it remained a distant prospect. The former was shown to be favourable for induction of labour, the latter unfavourable.
In practice, the application of a scoring system based on Bishop’s concept provides a reliable prediction of how successful labour induction is likely to be, but also of what method is most suitable ( Fig 8-3 ). If the cervical score ( Table 8-1 ) is high, labour is imminent and can usually be successfully induced by amniotomy alone, with or without oxytocin to stimulate uterine contractions. In cases where the cervix is unfavourable, cervical ripening is indicated before amniotomy and oxytocin. A variety of techniques have been in and out of vogue in the past 50 years. Although some of these may now seem primitive or bizarre, those which enjoyed any success had in common the provocation of those substances, especially oxytocin or prostaglandins, which participate in spontaneous labour. Thus, breast stimulation (which causes release of oxytocin), castor oil, enema, Foley catheters, Bougies, membrane sweeping and even sexual intercourse have had their advocates. All of the latter provide or provoke the release of prostaglandins.
| Cervical Feature | Pelvic Score | |||
|---|---|---|---|---|
| 0 | 1 | 2 | 3 | |
| Bishop Score | ||||
| Dilatation (cm) | 0 | 1–2 | 3–4 | 5–6 |
| Effacement (%) | 0–30 | 40–60 | 60–70 | 80+ |
| Station * (cm) | −3 | −2 | −1/0 | +1/+2 |
| Consistency | Firm | Medium | Soft | – |
| Position | Posterior | Mid-posterior | Anterior | – |
| Modified Bishop Score | ||||
| Dilatation (cm) | < 1 | 1–2 | 2–4 | > 4 |
| Length of cervix (cm) | > 4 | 2–4 | 1–2 | < 1 |
| Station * (cm) | −3 | −2 | –1/0 | +1/+2 |
| Consistency | Firm | Average | Soft | – |
| Position | Posterior | Mid; Anterior | – | – |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
