Interpretation
Our findings are similar to Du et al. [12] who also showed a 10 times lower risk of hyperstimulation in the double-balloon catheter group to the prostaglandin group. However, the time to first use of pain relief and the percentage not requiring pain relief in the first 12 hours was still similar in both groups, likely an inherent development in labour induction.
A recent systematic review [13] on the safety of the balloon catheter used a random effects model. It included 26 studies (8292 women) which estimated the prevalence of adverse events to be 0 to 0.26%, “pain and discomfort’ being most common. In this study, none of the included studies used a double balloon catheter. Our study provides more data to support the good safety profile of the double balloon catheter. Solt et al. [14] compared the Bishop score increment between a DBC and a single balloon catheter, he concluded that the DBC was more effective that the single balloon catheter with decreased time to delivery and decreased caesarean section rates. The usage of a single balloon catheter in induction of labour is off-licensed, and also requires traction.
Outpatient cervical ripening can be an attractive option because of the potential for lower costs and patient satisfaction. This is only possible if the method does not have an adverse effect on the fetus and does not require medical interventions. Less fetal monitoring may be required when DBC is used. In this regard, it may still be difficult for the double catheter balloon to fulfil this role fully, even without hyperstimulation, given the requirement for analgesia in the first 12 hours in 28.1% of the patients.
Wilkinson et al [9] ran a pilot randomised trial comparing inpatient and outpatient balloon induction, they found that patients in the outpatient arm felt less isolated and emotionally alone while medical staff including midwives and doctors were more comfortable with the use of a catheter as an option for outpatient ripening with 90% supporting outpatient ripening with the catheter. A local study[5] also showed that the use of DBC showed similar satisfaction and acceptability in the Singapore population, with 71% of patients recommending the DBC as the mode for IOL.
Du et al’s systemic review [12] of 9 randomized controlled studies concluded similar efficacy profiles between the double balloon catheter and the prostaglandin E2. Our study also showed similar labour outcomes in both groups with regards to recourse to caesarean deliveries, but identified the difference in reasons however. Caesarean delivery for failed induction was more common in the prostaglandin group and failure to progress in the first stage of labour more common in the DBC group. Average time to eventual delivery in both groups was similar. Our study, in particular, demonstrated a more predictable course of induction and significantly shorter time required with the DBC from the initiation of IOL to achieving a cervical dilation of more than 4 cm (91.3% vs 67.6%, p=<0.0001), although artificial rupture of membranes and augmentation are more frequently required. We believe this could offer significant advantage to obstetricians in planning inductions for their patients, as well as better patient satisfaction. A cost-efficacy study may be useful in evaluating a best method of induction.
Currently, there are 9 randomized controlled trials[6,15,16,17,18,19,20] involving a double balloon catheter. The balloon-filling regime is not standardized. In this trial, we used a standardized non-incremental balloon-filling regime prescribed according to the manufacturer’s advice. This decreased delays in achieving full inflation and decreased the time requiring intensive monitoring of the fetus; hence, we would recommend this as the standard balloon-filling regime for the double balloon catheter.