Birth progression and traction forces developed under vacuum extraction after slow or rapid application of suction.

A vacuum extraction recorder was used to provide an objective measure of the traction forces developed on the fetal head during 120 vacuum extractions. In half of the deliveries the vacuum was gradually and stepwise increased to -0.8 kg/cm2 before traction. In the others, a rapid application of vacuum to the same level was chosen. No significant difference could be recorded in the traction forces developed by the different methods. In fact, once an adequate level of vacuum had been achieved, high degrees of traction could be applied to the suction cup, regardless of the rate at which the vacuum was developed. Furthermore, the number and nature of neonatal complications were not influenced by the method chosen.