For a study, researchers sought to investigate the hypothesis that digital balloon catheter installation does not result in a higher risk of maternal infection than the speculum approach. Pregnant women undergoing induction of labor with an unfavorable cervix (less than 3 cm dilated and less than 60% effaced) were randomly allocated to a balloon catheter implanted digitally or using a sterile speculum in the open-label noninferiority randomized study. The primary outcome was a composite of maternal infection, as defined by the presence of fever (38°C or above), chorioamnionitis, or endometritis (diagnoses were made by the managing obstetric physician or midwife). Secondary endpoints that had been predetermined were primary composite outcomes, cesarean delivery rates, and maternal and neonatal outcomes. A study of patient satisfaction was also conducted. A sample size of 372 women was required based on a 10% noninferiority margin and a 10% primary outcome frequency (90% power to confirm noninferiority with 90% protocol adherence).
Three hundred seventy-two women were randomly assigned from February 2018 to February 2019. (185 digital placement, 187 sterile specula). The features of the groups at the start were comparable. The composite maternal infection rate was not different between groups (digital placement arm: 15.7% vs speculum arm: 12.8%), with an absolute difference of 2.8% (95% CI -4.3 to 9.9%) with respect to the sterile speculum arm, indicating noninferiority for the pre-specified margin. Except for a greater requirement for a second balloon catheter in the sterile speculum arm, secondary outcomes did not differ across groups. There were no differences in unfavorable maternal and neonatal events across groups. Women were similarly happy with the description of the approach before placement, concerned about the process, and discomfort during placement, regardless of the method of placement. The digital placement approach would be preferred by more women in the sterile speculum group (37.6% vs 25.7%; P=.02).
In terms of maternal infection, digital insertion of a balloon catheter for preinduction cervical ripening was non-inferior to the sterile speculum approach. Women in the sterile speculum group required a second round of the mechanical dilator more frequently. For balloon implantation for cervical ripening, the blind digital technique was a viable choice.