Rapid versus stepwise application of negative pressure in vacuum extraction-assisted vaginal delivery: a multicentre randomised controlled non-inferiority trial

Objective To evaluate whether the application of rapid negative pressure for vacuum-assisted delivery is as effective and safe as the stepwise method. Design Randomised controlled trial. Setting Six centres, including university, secondary and tertiary hospitals, in Thailand. Sample In total, 662 women were randomised to rapid and stepwise groups, with 331 women in each group. Methods Vacuum extraction was performed by applying a metal cup (Malmstrom) connected to an electric pump to the fetal head. The stepwise method consisted of four incremental steps of 0.2 kg/cm(2) every 2 minutes to obtain a final negative pressure of 0.8 kg/cm(2). In the rapid method the negative pressure of 0.8 kg/cm(2) was applied in one step in <2 minutes. Main outcome measures Success rate of vacuum extraction, vacuum cup detachment rate, duration of vacuum extraction, and maternal and neonatal complications. Results There were no significant differences in detachment rates (RD 0.3%, 95% CI -3.1 to 2.4). The overall success rates were identical, at 98.2%. There were significant reductions in the time between applying the vacuum cup and attaining maximum negative pressure (MD -4.6 minutes; 95% CI -4.4 to -4.8 minutes), and in the time between applying the cup and delivery (MD -4.4 minutes; 95% CI -4.8 to -4.0 minutes). There was a significantly higher rate of perineal suture in the rapid method group (RD 4.5%; 95% CI 1.1-8.2). There were no significant differences in maternal and fetal morbidities. Conclusions Rapid negative pressure vacuum extraction could be performed as effectively and safely as the stepwise method, in a shorter period of time.