Oxytocin in high versus low doses for augmentation of delayed labour

Women have different lengths of labour, with first labours lasting on average eight hours (and unlikely to last more than 18 hours) and second and subsequent labours lasting an average of five hours and unlikely to last more than 12 hours. Assessment of progress in labour takes into account not just cervical dilatation, but also descent and rotation of the fetal head and the strength, duration and frequency of contractions. Some evidence suggests that up to one-third of women in their first labour experience delay. They are often given a synthetic version of the hormone oxytocin  to increase uterine contractions and shorten labour. Surprisingly for such a routine treatment, the ideal dose at which it should be given is not known, although some comparisons suggest that higher-dose regimens of oxytocin could shorten labour and reduce the chance of caesarean section with an increase in the numbers of women having a spontaneous vaginal birth compared with lower-dose regimens. However, there are potentially harmful side effects as oxytocin may cause the uterus to contract too quickly, and the baby to become distressed. Clinicians attempt to mitigate these side effects by adjusting the dose of oxytocin with the contractions to reduce the chances of the baby being distressed in labour.

From the four randomised controlled trials involving 644 pregnant women that we included in this review, results indicate that a higher dose of oxytocin (4-7 mU per minute, compared with 1-2 mU per minute) reduced the length of labour and the rate of caesarean sections with increased spontaneous vaginal births, but the studies did not provide enough evidence on possible differences between the high- and low-dose regimens on adverse events including hyperstimulation of the uterus, and outcomes for the newborn infant. Only one trial reported on the possible effect on women. The overall quality of the included trials was mixed, but this might reflect how clinical trials were reported in the past.  

While the current evidence is promising and suggests that the high-dose regimens reduce the length of labour and the rate of caesarean sections, this evidence is not strong enough to recommend that high-dose regimens are used routinely for women delayed in labour. We recommend that further research is carried out. 

Authors' conclusions: 

Higher-dose regimens of oxytocin (4 mU per minute or more) were associated with a reduction in the length of labour and in caesarean section, and an increase in spontaneous vaginal birth. However, there is insufficient evidence to recommend that high-dose regimens are advised routinely for women with delay in the first stage of labour. Further research should evaluate the effect of high-dose regimens of oxytocin for women delayed in labour and should include maternal and neonatal outcomes as well as the effects on women.

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Background: 

A major cause of failure to achieve spontaneous vaginal birth is delay in labour due to presumed inefficient uterine action. Oxytocin is given to increase contractions and high-dose regimens may potentially increase the number of spontaneous vaginal births, but as oxytocin can cause hyperstimulation of the uterus, there is a possibility of increased adverse events.

Objectives: 

To compare starting dose and increment dose of oxytocin for augmentation for women delayed in labour to determine whether augmentation by high-dose regimens of oxytocin improves labour outcomes and to examine the effect on both maternal/neonatal outcomes and women's birth experiences.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 May 2013) and reference lists of retrieved studies.

Selection criteria: 

We included all randomised and quasi-randomised controlled trials for women in delayed labour requiring augmentation by oxytocin comparing high-dose regimens (defined as starting dose and increment of equal to or more than 4 mU per minute) with low-dose regimens (defined as starting dose and an increment of less than 4 mU per minute). Increase interval: between 15 and 40 minutes. The separation of low- and high-dose regimens is based on an arbitrary decision.

Data collection and analysis: 

Four review authors undertook assessment of trial eligibility, risk of bias, and data extraction independently.

Main results: 

We included four studies involving 644 pregnant women. Three studies were randomised controlled trials and one trial was a quasi-randomised study. A higher dose of oxytocin was associated with a significant reduction in length of labour reported from one trial (mean difference (MD) -3.50 hours; 95% confidence interval (CI) -6.38 to -0.62; one trial, 40 women). There was a decrease in the rate of caesarean section (risk ratio (RR) 0.62; 95% CI 0.44 to 0.86 four trials, 644 women) and an increase in the rate of spontaneous vaginal birth in the high-dose group (RR 1.35; 95% CI 1.13 to 1.62, three trials, 444 women), although for both of these outcomes there were inconsistencies between studies in the size of effect. When we carried out sensitivity analysis (temporarily removing a study at high risk of bias) the differences between groups were no longer statistically significant

There were no significant differences between high- and low-dose regimens for instrumental vaginal birth, epidural analgesia, hyperstimulation, postpartum haemorrhage, chorioamnionitis or women's perceptions of experiences. For neonatal outcomes, there was no significant difference between groups for Apgar scores, umbilical cord pH, admission to special care baby unit, or neonatal mortality. The following outcomes were not evaluated in the included studies: perinatal mortality, uterine rupture, abnormal cardiotocography, women's pyrexia, dystocia and neonatal neurological morbidity.

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