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

Abstract

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/cm² every 2 minutes to obtain a final negative pressure of 0.8 kg/cm². In the rapid method the negative pressure of 0.8 kg/cm² 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.