Mechanical methods for induction of labour

Labour induction is a common obstetric procedure that is carried out when the risk of continuing pregnancy outweighs the benefits.

Mechanical methods of induction were developed to promote cervical ripening and the onset of labour by stretching the cervix. They are amongst the oldest methods to initiate labour. More recently pharmacological prostaglandins (vaginal and intracervical prostaglandin E2, vaginal and oral misoprostol) and oxytocin have partly replaced mechanical methods. The goal of this review of 71 randomised controlled trials (9722 women) was to determine the effects of mechanical methods for cervical ripening or induction of labour in comparison with no treatment, prostaglandins and oxytocin for women in the third trimester of pregnancy.

The review includes 71 randomised controlled trials (total of 9722 women), ranging from 39 to 588 women per study. Most studies reported on caesarean section; all other outcomes are based on substantially fewer women. Mechanical methods were as effective as prostaglandins in achieving delivery within 24 hours of the start of the intervention, with fewer episodes of excessive uterine contractions. The risk of caesarean section did not differ. Few studies addressed the issue of infection, which appeared not to be higher when using mechanical methods. Thus mechanical methods can be considered to have less side effects compared with prostaglandins. The one study that reported on maternal discomfort showed more discomfort during ripening with prostaglandins compared with Foley catheter insertion, and with double balloon devices compared with Foley catheters. This outcome may influence the choice of method and is an important issue to be addressed in future studies. Mechanical methods were more effective than induction with oxytocin. Serious neonatal and maternal ill effects were not often reported and did not differ between the interventions.

Authors' conclusions: 

Induction of labour using mechanical methods results in similar caesarean section rates as prostaglandins, for a lower risk of hyperstimulation. Mechanical methods do not increase the overall number of women not delivered within 24 hours, however the proportion of multiparous women who did not achieve vaginal delivery within 24 hours was higher when compared with vaginal PGE2. Compared with oxytocin, mechanical methods reduce the risk of caesarean section.

Read the full abstract...
Background: 

Mechanical methods were the first methods developed to ripen the cervix and induce labour. During recent decades they have been substituted by pharmacological methods. Potential advantages of mechanical methods, compared with pharmacological methods, may include simplicity of preservation, lower cost and reduction of the side effects.

Objectives: 

To determine the effects of mechanical methods for third trimester cervical ripening or induction of labour in comparison with placebo/no treatment, prostaglandins (vaginal and intracervical prostaglandin E2 (PGE2), misoprostol) and oxytocin.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 April 2011) and bibliographies of relevant papers. We updated this search on 16 January 2012 and added the results to the awaiting classification section of the review.

Selection criteria: 

Clinical trials comparing mechanical methods used for third trimester cervical ripening or labour induction with methods listed above it on a predefined list of methods of labour. A comparison with amniotomy will be added, should this comparison be made in future trials.

Different types of intervention have been considered as mechanical methods: (1) introduction of laminaria tents, or their synthetic equivalent (Dilapan), into the cervical canal; (2) the introduction of a catheter through the cervix into the extra-amniotic space, with or without traction; (3) use of a catheter to inject fluidsin the extra-amniotic space

In addition, we made other comparisons: (1) specific mechanical methods (balloon catheter and laminaria tents) compared with any prostaglandins or with oxytocin; (2) addition of prostaglandins or oxytocin to mechanical methods compared with prostaglandins alone.

Data collection and analysis: 

Two review authors independently assessed trials for inclusion and assessed risk of bias. Two review authors independently extracted data.

Main results: 

For this update we have included a further 27 studies. The review includes 71 randomised controlled trials (total of 9722 women), ranging from 39 to 588 women per study. Most studies reported on caesarean section, all other outcomes are based on substantially fewer women. Four additional studies are ongoing.

Mechanical methods versus no treatment: one study (48 woman) reported on women who did not achieve vaginal delivery within 24 hours (risk ratio (RR) 0.90; 95% confidence interval (CI) 0.64 to 1.26). The risk of caesarean section was similar between groups (six studies; 416 women, RR 1.00; 95% CI 0.76 to 1.30). There were no cases of severe neonatal and maternal morbidity.

Mechanical methods versus vaginal PGE2 (17 studies;1894 woman): The proportion of women who did not achieve vaginal delivery within 24 hours was not significantly different (three studies; 586 women RR 1.72; 95% CI 0.90 to 3.27); however, for the subgroup of multiparous women the risk of not achieving delivery within 24 hours was higher (one study; 147 women RR 4.38, 95% CI 1.74 to 10.98), with no increase in caesarean sections (RR 1.19, 95% CI 0.62-2.29). Compared with intracervical PGE2 (14 studies;1784 women and misoprostol there was no significant difference in the proportion of women not achieving vaginal delivery within 24 hours.

Mechanical methods reduced the risk of hyperstimulation with fetal heart rate changes when compared with vaginal prostaglandins: vaginal PGE2 (eight studies; 1203 women, RR 0.16; 95% CI 0.06 to 0.39) and misoprostol (3% versus 9%) (nine studies; 1615 women, RR 0.37; 95% CI 0.25 to 0.54). Risk of caesarean section between mechanical methods and prostaglandins was comparable. Serious neonatal and maternal morbidity were infrequently reported and did not differ between the groups.

Mechanical methods compared with induction with oxytocin (reduced the risk of caesarean section (five studies; 398 women, RR 0.62; 95% CI 0.42 to 0.90). The likelihood of vaginal delivery within 24 hours was not reported. Hyperstimulation with fetal heart rate changes was reported in one study (200 participants), and did not differ. There were no reported cases of severe maternal or neonatal morbidity.