Mechanical methods for induction of labour

We set out to determine from randomised controlled trials the effectiveness and safety of mechanical methods to bring on labour in the third trimester of pregnancy (> 24 weeks' gestation). Use of a balloon to stretch the cervix (the lower end of the uterus) was compared with prostaglandin E2 (PGE2), low-dose misoprostol or oxytocin.

What is the issue?

Induction is carried out generally when the risk of continuing pregnancy outweighs the benefits, or at the request of pregnant women.

Mechanical methods for induction promote cervical ripening and onset of labour by stretching the cervix. They are amongst the oldest methods used to initiate labour. During the last decades, medication such as PGE2, misoprostol and oxytocin have partly replaced mechanical methods.

Why is this important?

More and more women have labour induced and indications are often not urgent. This means that the safety aspects of induction methods become more important, although this could be at the expense of effectiveness. Mechanical methods could have advantages over pharmacological methods as they are widely available, low in cost and may have fewer side effects, such as excessive contractions of the uterus (uterine hyperstimulation). This could potentially be safer for the baby because if contractions are too long or very close together, the baby may not receive sufficient oxygen.

What evidence did we find?

For this review we included a total of 113 randomised controlled trials involving 22,373 women who were scheduled for induction of labour for different indications. The data contributed to 21 different comparisons and 20 subgroup comparisons. Overall, the evidence was graded from very low to moderate quality. For many comparisons there were too few women in the trials to determine any clear differences in serious illness for mothers and babies.

Twenty-eight trials (6619 women) showed mechanical induction with a balloon is as effective as vaginal PGE2 as there may be little or no difference in vaginal deliveries within 24 hours and there probably is little or no difference in caesarean sections between groups. However, a balloon appears to be safer for the neonate as it probably reduces the risk of uterine hyperstimulation with an abnormal heart rate of the baby, serious illness or death of the baby and may slightly reduce the risk for a neonatal intensive care unit admission. It was unclear if there was a difference in serious illness or death of the mother or in the five-minute Apgar score less than seven.

Thirteen trials (1818 women) compared induction of labour with a balloon with vaginal misoprostol and showed a balloon probably reduces the risk of uterine hyperstimulation with an abnormal heart rate of the baby, but may increase the risk of a caesarean section. It was unclear if there was a difference in vaginal deliveries within 24 hours, serious illness or death of the baby, serious illness or death of the mother, five-minute Apgar score less than seven or neonatal intensive care unit admissions.

Seven trials (3178 women) showed a balloon may be less effective than oral misoprostol as a balloon probably increases the risk of a vaginal delivery not achieved within 24 hours and probably slightly increases the risk of a caesarean section. Data on safety are still unclear as it is uncertain whether there is a difference in uterine hyperstimulation with an abnormal heart rate of the baby, serious illness or death of the baby, serious illness or death of the mother, five-minute Apgar score less than seven or neonatal intensive care unit admissions.

What does this mean?

Mechanical induction with a balloon is probably as effective as induction of labour with vaginal PGE2. However, a balloon seems to have a more favourable safety profile for the baby. More research on this comparison does not seem warranted.

A balloon catheter may be slightly less effective as oral misoprostol, but It remains unclear if there is a difference in safety outcomes for the baby. When compared to low-dose vaginal misoprostol, a balloon catheter may be less effective, but probably has a better safety profile for the baby.

Future research could focus more on safety aspects for the baby and maternal satisfaction.

Authors' conclusions: 

Low- to moderate-quality evidence shows mechanical induction with a balloon is probably as effective as induction of labour with vaginal PGE2. However, a balloon seems to have a more favourable safety profile. More research on this comparison does not seem warranted.

Moderate-quality evidence shows a balloon catheter may be slightly less effective as oral misoprostol, but it remains unclear if there is a difference in safety outcomes for the neonate. When compared to low-dose vaginal misoprostol, low-quality evidence shows a balloon may be less effective, but probably has a better safety profile.

Future research could be focused more on safety aspects for the neonate and maternal satisfaction.

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 reduction in side effects that could improve neonatal outcomes. This is an update of a review first published in 2001, last updated in 2012.

Objectives: 

To determine the effectiveness and safety of mechanical methods for third trimester (> 24 weeks' gestation) induction of labour in comparison with prostaglandin E2 (PGE2) (vaginal and intracervical), low-dose misoprostol (oral and vaginal), amniotomy or oxytocin.

Search strategy: 

For this update, we searched Cochrane Pregnancy and Childbirth’s Trials Register, ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP), and reference lists of retrieved studies (9 January 2018). We updated the search in March 2019 and added the search 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 pharmacological methods.

Mechanical methods include: (1) the introduction of a catheter through the cervix into the extra-amniotic space with balloon insufflation; (2) introduction of laminaria tents, or their synthetic equivalent (Dilapan), into the cervical canal; (3) use of a catheter to inject fluid into the extra-amniotic space (EASI).

This review includes the following comparisons: (1) specific mechanical methods (balloon catheter, laminaria tents or EASI) compared with prostaglandins (different types, different routes) or with oxytocin; (2) single balloon compared to a double balloon; (3) addition of prostaglandins or oxytocin to mechanical methods compared with prostaglandins or oxytocin alone.

Data collection and analysis: 

Two review authors independently assessed trials for inclusion and assessed risk of bias. Two review authors independently extracted data and assessed the quality of the evidence using the GRADE approach.

Main results: 

This review update includes a total of 113 trials (22,373 women) contributing data to 21 comparisons. Risk of bias of trials varied. Overall, the evidence was graded from very-low to moderate quality. All evidence was downgraded for lack of blinding and, for many comparisons, the effect estimates were too imprecise to make a valid judgement.

Balloon versus vaginal PGE2: there may be little or no difference in vaginal deliveries not achieved within 24 hours (average risk ratio (RR) 1.01, 95% confidence interval (CI) 0.82 to 1.26; 7 studies; 1685 women; I² = 79%; low-quality evidence) and there probably is little or no difference in caesarean sections (RR 1.00, 95% CI 0.92 to 1.09; 28 studies; 6619 women; moderate-quality evidence) between induction of labour with a balloon catheter and vaginal PGE2. A balloon catheter probably reduces the risk of uterine hyperstimulation with fetal heart rate (FHR) changes (RR 0.35, 95% CI 0.18 to 0.67; 6 studies; 1966 women; moderate-quality evidence), serious neonatal morbidity or perinatal death (RR 0.48, 95% CI 0.25 to 0.93; 8 studies; 2757 women; moderate-quality evidence) and may slightly reduce the risk of a neonatal intensive care unit (NICU) admission (RR 0.82, 95% CI 0.65 to 1.04; 3647 women; 12 studies; low-quality evidence). It is uncertain whether there is a difference in serious maternal morbidity or death (RR 0.20, 95% CI 0.01 to 4.12; 4 studies; 1481 women) or five-minute Apgar score < 7 (RR 0.74, 95% CI 0.49 to 1.14; 4271 women; 14 studies) because the quality of the evidence was found to be very low and low, respectively.

Balloon versus low-dose vaginal misoprostol: it is uncertain whether there is a difference in vaginal deliveries not achieved within 24 hours between induction of labour with a balloon catheter and vaginal misoprostol (RR 1.09, 95% CI 0.85 to 1.39; 340 women; 2 studies; low-quality evidence). A balloon catheter probably reduces the risk of uterine hyperstimulation with FHR changes (RR 0.39, 95% CI 0.18 to 0.85; 1322 women; 8 studies; moderate-quality evidence) but may increase the risk of a caesarean section (average RR 1.28, 95% CI 1.02 to 1.60; 1756 women; 12 studies; I² = 45%; low-quality evidence). It is uncertain whether there is a difference in serious neonatal morbidity or perinatal death (RR 0.58, 95% CI 0.12 to 2.66; 381 women; 3 studies), serious maternal morbidity or death (no events; 4 studies, 464 women), both very low-quality evidence, and five-minute Apgar score < 7 (RR 1.00, 95% CI 0.50 to 1.97; 941 women; 7 studies) and NICU admissions (RR 1.00, 95% CI 0.61 to 1.63; 1302 women; 9 studies) both low-quality evidence.

Balloon versus low-dose oral misoprostol: a balloon catheter probably increases the risk of a vaginal delivery not achieved within 24 hours (RR 1.28, 95% CI 1.13 to 1.46; 782 women, 2 studies, and probably slightly increases the risk of a caesarean section (RR 1.17, 95% CI 1.04 to 1.32; 3178 women; 7 studies; both moderate-quality evidence) when compared to oral misoprostol. It is uncertain whether there is a difference in uterine hyperstimulation with FHR changes (RR 0.81, 95% CI 0.48 to 1.38; 2033 women; 2 studies), serious neonatal morbidity or perinatal death (RR 1.11, 95% CI 0.60 to 2.06; 2627 women; 3 studies), both low-quality evidence, serious maternal morbidity or death (RR 0.50, 95% CI 0.05 to 5.52; 2627 women; 3 studies), very low-quality evidence, five-minute Apgar scores < 7 (RR 0.71, 95% CI 0.38 to 1.32; 2693 women; 4 studies) and NICU admissions (RR 0.82, 95% CI 0.58 to 1.17; 2873 women; 5 studies) both low-quality evidence.

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