Induction of labour

Induction of labour may be considered beneficial in many clinical circumstances. These include fetal growth restriction (or other states of potential fetal compromise), spontaneous rupture of membranes, pre‐eclampsia, and post‐term pregnancy. The effects of induction of labour in some specific clinical situations are assessed in other Cochrane reviews (e.g. Boulvain 2001a; Gülmezoglu 2006; Irion 1999).

A review of the evidence‐base for labour induction indications found that recommendations for induction of labour for post‐term gestation, premature rupture of membranes at term, and premature rupture of membranes near term with pulmonary maturity are supported by evidence; induction for fetal growth impairment before term reduces intrauterine fetal death, but increases caesarean deliveries and neonatal deaths; evidence is insufficient to support induction for women with insulin‐requiring diabetes, twin gestation, fetal macrosomia, oligohydramnios, cholestasis of pregnancy, maternal cardiac disease and fetal gastroschisis (Mozurkewich 2009).  On the other hand, risk‐guided preventive labour induction is claimed to improve birth outcomes (Nicholson 2009). Labour induction, for clinical indications, if performed, usually takes place during the third trimester of pregnancy (after 28 weeks).

Labour may also be induced for social reasons, e.g., to coincide with planned leave from work by the woman or her partner (Crosby 2008).  Labour induction tends to be more common in women who live far from obstetric services (Kornelsen 2009).

Recently, emphasis has been placed on the value of avoiding elective delivery before 39 weeks’ gestation due to increased rates of neonatal high care admissions (Clark 2009). A specific program to reduce early term elective deliveries has been found to be effective (Oshiro 2009), as has labour induction guidelines backed by medical staff education (Fisch 2009).

Labour induction in the evening (for example, at about 2100 hours) has been found to be associated with similar labour duration and improved neonatal outcome than that commenced in the morning (Bakker 2009).

Methods for inducing labour

When a woman and her caregivers agree that labour induction is necessary (or desirable), the best method of induction needs to be chosen. The main problems experienced during induction of labour are an inability to achieve effective labour, or the production of excessively strong uterine contractions. The latter may cause both maternal and fetal distress, and both problems may lead to an increased risk of caesarean section. Excessive uterine activity, through inappropriate use of uterine stimulants, may occasionally lead to the very serious complication of uterine rupture (and fetal death).

There is considerable variation in how women perceive induction of labour. At one end of the continuum are women who dislike the idea of induction intensely. At the other end of the continuum are women who welcome interventions to bring the birth of their baby forward. Whilst there are legitimate reasons to debate what is a desirable rate of induction of labour in any population of pregnant women, and whether in some settings this rate is much higher than it should be, that is not the objective of this protocol and its daughter reviews. These focus specifically on methods, not use and abuse.

There are several clinical factors which may influence the choice of induction method. These include parity, the condition of the cervix, membrane status, and presence or absence of a uterine scar (usually from a previous caesarean section).

Parity is important because women tend to be more sensitive (and sometimes much more sensitive) to stimulatory drugs if they have had a baby (or babies) previously. In a recent observational study, nulliparous women with an undilated cervix whose labours were electively induced had a 50% caesarean section rate (Clark 2009).

The state of the woman's cervix can be assessed by vaginal examination and 'scored' (Bishop 1964) to make a semi‐quantitative prediction of 'favourability' for labour induction. Induction tends to be easier if the cervix is soft, dilated, and short (favourable/high cervical score) and more difficult if firm, closed and long (unfavourable/low cervical score). When the cervix is unfavourable, prostaglandin preparations are often used (Keirse 1993; MacKenzie 1997) although these may be particularly associated with uterine hyperstimulation (Egarter 1990). More recently, ultrasound measurements of cervical length and distance from the perineum to the baby’s head have been suggested as additional parameters for assessment of cervical readiness (Eggebø 2009). Ultrasound measurement of cervical length and body mass index were found to be better predictors of caesarean section than the clinical cervical score (Uyar 2009).

Women whose membranes have already ruptured may respond differently to stimulatory drugs than those whose membranes are still intact at the time of labour induction. The drainage of amniotic fluid through the vagina may also flush out locally applied medication. The presence of a uterine scar carries a risk of dehiscence during labour, especially if uterine activity is excessive. Though uncommon, this is potentially a very serious complication that can pose a threat to the lives of both baby and mother.

There are many methods of labour induction that include administration of oxytocin; prostaglandins; prostaglandin analogues and smooth muscle stimulants, such as herbs or castor oil; or mechanical methods, such as digital stretching of the cervix and sweeping of the membranes; hygroscopic cervical dilators; extra‐amniotic balloon catheters; artificial rupture of the membranes; and nipple stimulation. Acupuncture and homeopathy have also been used. Because of the scale of this topic and the multiplicity of trials comparing one method with others and the potential for duplication of effort, members of the Cochrane Pregnancy and Childbirth Group decided to address this subject strategically. We developed a common methodology and panel of outcome measures for all labour induction reviews. In addition, we devised a strategy whereby each comparison has a single 'home' review (e.g., comparison of mifepristone versus vaginal misoprostol would appear only in the mifepristone review ‐ seeData collection and analysis).

We decided to combine techniques that aim to ripen the cervix (make it more soft, short and open) and those that aim to induce labour. As mentioned above, prostaglandins are frequently used to ripen the cervix when it is 'unfavourable' but this commonly causes labour to start. We therefore felt that the distinction between ripening and labour induction is, in practice, artificial.

This protocol forms the basis of a series of reviews of methods of labour induction ‐ seeMethods for more detailed information. It differs from other protocols published in The Cochrane Library because it will be retained permanently as a protocol to describe the methods that shaped the production of all labour induction reviews, unlike other Cochrane protocols which usually develop into full reviews. In addition to the general background in this generic protocol, each of the individual induction of labour reviews will include its own method‐specific background information.