Inpatient versus outpatient induction of labour: a systematic review and meta-analysis

Labour induction, the artificial initiation of labour when the benefits of delivery are deemed greater than those of expectant management, is a common obstetric procedure that precedes labour in as many as one in four pregnancies [1‐3]. However, labour induction, especially in nulliparous women, and when an unfavourable cervix requires priming or ripening, could take a considerable amount of time, ranging from several hours to a couple of days [1, 2]. Outpatient cervical ripening can be an attractive option to theoretically reduce length of antenatal stay in hospital, reduce strain on healthcare resources, increase maternal satisfaction and comfort, and potentially reduce financial costs. Thus, the practice of outpatient cervical ripening using mechanical or pharmacological agents is gaining popularity around the world. However, its uptake remains highly variable [4, 5], presumably due to a number of cultural and resource-related factors, as well as concerns with regard to its safety and efficacy. We sought to systematically review the literature, reporting all randomized controlled trials that compared outpatient to inpatient labour induction, to evaluate its safety and efficacy.

The study was conducted and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [6].

This systematic review comparing outpatient vs. inpatient labour induction identified 12 publications representing nine trials that included 2615 pregnancies. Overall, there were no differences between the groups in any of the outcomes except for a higher incidence of suspicious fetal heart rate tracings, a shorter mean length of hospital stay in the outpatient induction arm. The higher incidence of suspicious fetal heart rate tracings did not translate to higher caesarean deliveries or neonatal adverse outcomes. In the subgroup analysis, which was only possible for studies comparing labour induction with balloon catheters in both arms, those induced as outpatients had fewer caesarean deliveries, a shorter admission-to-delivery interval, and a shorter induction-to-delivery interval.

Although outpatient labour induction is gaining acceptance, some centres still refrain from performing these procedures, based on the lack of strong evidence with regard to its safety. This systematic review of randomized controlled trials shows that outpatient induction is at least as safe and effective as inpatient induction in terms of maternal, neonatal and resource-related outcomes. While all patient-reported outcomes only had a sample size of one study, differences of these independent proportions showed patients undergoing outpatient ripening experienced significantly less discomfort and would more likely choose the method of ripening again. Although suspicious fetal heart rate tracings were higher in the outpatient group, it must be noted that these were not measured in a similar manner, in the two arms. For example, one study reported on fetal heart rate tracing at 12 h in the inpatient arm and at 24 h in the outpatient arm. The role of an outcome assessor in determining a subjective outcome such as a suspicious heart rate tracing should also be taken into consideration while interpreting this finding. Finally, it must be noted that the difference was only noted for ‘suspicious’ tracings and not pathological tracings, and also that this did not result in higher caesarean deliveries or adverse neonatal outcomes.

The findings of the subgroup analysis are particularly interesting, as there were four studies that included the same method (balloon catheters) in both arms, thereby allowing meaningful comparison. Here it was noted that although those being induced as outpatients had a higher mean duration of oxytocin use, they had significantly fewer caesarean deliveries as compared with those being induced as inpatients, and a shorter admission-to-delivery interval of approximately nine hours (527 min), with no increase in adverse maternal or neonatal outcomes. Resource-use and costs are highly dependent on the efficiency of the setup for outpatient inductions. Although this systematic review did not show cost differences, this could be related to the absence of less resource-intense protocols for outpatient induction, including the involvement of nurse practitioners, physician-assistants, nurses and midwives, rather than obstetricians to perform the outpatient cervical ripening in an office setting, instead of over-saturating existing infrastructures in triage or on the delivery floor.

Our study is the most up-to-date review comparing inpatient vs. outpatient labour induction. The included studies were all randomized controlled trials with low-to-moderate risk-of-bias, and included various methods of induction used in contemporary practice. We employed a rigorous methodology and a comprehensive search strategy, and included a pragmatic subgroup analysis. Despite these strengths, there are some limitations to our study. First, there is significant clinical heterogeneity in our main analysis, which pooled all of the five induction methods together. Furthermore, some included studies used different induction methods in the inpatient and outpatient arms, making it difficult to compare results from these studies, as it is unclear whether the between-group differences were the result of the setting or the induction methods used. Naturally, each of the different mechanical or pharmacological induction method has a different mechanism of action, as well as safety and adverse-effect profile. In order to try to tease out the nuances in safety and efficacy outcomes, we performed a subgroup analysis based on studies that compared the same induction methods in both the inpatient and outpatient arms. Second, despite induction of labour being employed in approximately 25% of all pregnancies, globally [4, 22, 23], there were only a limited number of trials that compared inpatient vs. outpatient induction, representing less than 3000 participants. However, the included studies were all well-conducted randomized controlled trials, adding credibility to the findings. Third, the variation in choice of the method of induction precluded subgroup analysis for most methods, as these were only represented by a single trial. The multitude of induction techniques and low sample size preventing meaningful comparisons between trials is a common dilemma when looking at labour induction [24]. Fourth, the theoretical advantages of outpatient induction are the potential in resource-savings and patient comfort. Only two trials reported on cost outcomes, but they used different outcomes metrics, so a pooled comparison was not possible. In addition, three trials investigated patient reported outcomes such as satisfaction and comfort. Fifth, the included studies, used a one-size-fits-all approach to labour induction, comparing a pre-determined method in each arm, regardless of the cervical status, uterine activity, parity and other patient characteristics that are could influence the effectiveness and safety of labour induction [25‐27]. Ideally, the method of choice for cervical ripening or labour induction should consider these parameters, and individualize care, to ensure the highest possible chance of a vaginal birth, with the lowest risk of adverse events. Finally, all trials took place in North America, Europe, or Australia, which are all resource-rich settings. In addition, all trials had strict inclusion criteria, and only included “low-risk” women in high-resource settings. These findings may therefore not be applicable to low-resource settings or different pregnancy populations.

In conclusion, this systematic review of randomized controlled trials comparing inpatient vs. outpatient labour induction reveals that outpatient labour induction in resource-rich settings is at least as effective and safe, if not more, in carefully-selected patient populations, when compared with inpatient inductions. While the results of this systematic review showed a shorter mean length of hospital admission for the outpatient group, the cost implications of this were only reported in one study, which showed no differences in costs. While the reason for this could be multifactorial, at this point there are insufficient data to make definitive conclusions regarding the cost-effectiveness of inducing labour in an outpatient setting. While there may be a need for larger multi-centered randomized controlled trials in diverse settings to determine the cost-effectiveness of outpatient labour induction, and a more pragmatic approach to the conduct of these trials [24], the findings of this systematic review suggest that outpatient induction for low-risk women is a safe, viable and effective alternative to inpatient induction, especially in resource-rich settings, and should be considered more universally, in contemporary obstetrics, where labour, in an increasing proportion of pregnancies are being induced.