Amniotomy for shortening spontaneous labour

This review produced no evidence in support of a policy of routine amniotomy for reducing the duration labour in either primigravid or multiparous women. Rather, the review suggests that amniotomy may increase the need for additional interventions such as caesarean section.

RHL Commentary by Wolomby JJ and Tozin RR

1. INTRODUCTION

Amniotomy (also known as artificial rupture of membranes) has long been believed to reduce the duration of labour, as suggested by available literature (1–6). Many health-care providers believe that shortening the duration of labour is beneficial and use amniotomy to reduce the risk of maternal morbidity in cases of complicated and prolonged labour. Amniotomy is also used when it is judged important to conduct internal monitoring of the fetus or to obtain amniotic fluid for visual inspection. The mechanism of action behind amniotomy is thought to be the release of prostaglandin E2 (PGE2) and rise in oxytocin level.

Opponents of amniotomy argue that the amniotic sac and fluid play an important role in protecting the fetus against uterine contractions, helping with cervical modifications (ripening, effacement and dilatation) and pre-stretching the perineum. It is believed that the pressure exerted by the membranes on the uterus stimulates oxytocin surges (7). At term, the amnion and cervix produce PGE2, which causes the cervix to soften and shorten. Meanwhile, the chorion produces the enzyme prostaglandin dehydrogenase, which breaks down PGE2, thus preventing premature delivery. Also at term, the part of the chorion that is in direct contact with the opening of the cervix releases less prostaglandin dehydrogenase, which allows the PGE2 from amnion to reach the cervix, resulting in ripening and effacement. If amniotomy is performed too early, it can slow the process of labour and increase the hourly rate of severe variable fetal heart deceleration.

The aim of this Cochrane Review was to determine the effectiveness and safety of routine use of amniotomy for reducing the duration of labour (prolonged or not) that starts spontaneously.

2. METHODS

For this review (8), the authors sought to include only randomized controlled trials that had compared amniotomy alone with intention to preserve the membranes. Trial participants included pregnant women of any parity and gestational age (at the time of entry into the trial) who had a singleton pregnancy and who had entered labour spontaneously.

The authors identified relevant studies from the Cochrane Pregnancy and Childbirth Group’s Trial Register by contacting the Trials Search Co-ordinator. Two reviewers assessed independently the validity of each study considered for inclusion. They extracted data about four primary outcomes (duration of first stage of labour, caesarean section, maternal satisfaction with childbirth experience, and Apgar score less than seven at five minutes or less than four at one minute) and 25 secondary outcomes. None of the outcomes were consistently reported in all the trials considered. Thus, it was not possible to perform subgroup analyses for all the outcomes.

3. RESULTS

A total of 14 randomized controlled trials involving 4893 women were included in the review. With regard to the four primary outcomes, the review found no statistically significant reduction [weighted mean difference (WMD) -20.43 minutes; 95% confidence interval (CI) -95.93−55.06] in the length of the first stage of labour, even when subgroups of multiparous and primigravid women were assessed independently. There was an increase in the risk of delivery by caesarean section in the amniotomy group, but the difference was not statistically significant and subgroup analyses of primigravid women only and multiparous women only gave the same result. There was also no statistically significant difference between the two groups (amniotomy and no amniotomy) in terms of maternal satisfaction with the childbirth experience. Overall, the analysis showed that babies of women in the amniotomy group were less likely to have an Apgar score of less than seven at five minutes, but the difference was not statistically significant. However, in the subgroup of primigravid women, those in the amniotomy group had a statistically significantly reduced risk of having a baby with an Apgar score of less than seven at five minutes [relative risk (RR) 0.42; 95% CI 0.20−0.88].

With regard to secondary outcomes, the review found no statistically significant difference in the duration of the second stage of labour between the amniotomy and the no amniotomy groups (WMD -2.38, 95% CI -5.27−0.50). In the subgroup of only primiparous women, there was a statistically significant reduction (WMD -6.59; 95% CI -12.34 to -0.84) in the length of second stage of labour in the amniotomy group. Two trials also found that the amniotomy group had a significantly (RR 0.75, 95% CI 0.64–0.88) reduced risk of dysfunctional labour (defined by the authors as "no progress in cervical dilatation in two hours or ineffective uterine contractions"). The review did not find any other statistically significant differences for the remaining maternal and perinatal outcomes.

4. DISCUSSION

4.1. Applicability of the results

Although most of the trials included in this review were conducted in Canada, the United Kingdom and USA there is no biological reason to expect that similar trials in under-resourced settings would produce different results. Therefore, the results of the review are relevant to under-resourced settings.

4.2. Implementation of the intervention

As such, amniotomy can be performed easily in all settings by a skilled attendant: its use involves neither extra cost nor special skills. If amniotomy is performed in primiparous women to reduce the risk of dysfunctional labour, it should be done in a facility where caesarean section can be performed, if required. In settings where the practice is to leave the membranes intact for as long as possible, that policy can be continued.

4.3. Implications for research

The authors of the review encountered many difficulties in gathering data on this topic due to the difference between research protocols. Further large well-designed multicentre randomized controlled trials with clear allocation concealment are needed.

Source of support: None

Acknowledgements: None

References

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This document should be cited as: Wolomby JJ and Tozin RR. Amniotomy for shortening spontaneous labour: RHL commentary (last revised: 5 January 2009). The WHO Reproductive Health Library; Geneva: World Health Organization.

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