Force and pressure measurement during vacuum extractions in obstetrics

The article describes the design and calibration of the measurement device and gives examples of measurement results found on a phantom and during actual delivery.

In vacuum extractions in obstetrics a tractive force is applied to the cranium of the baby using a suction device known as a suction cup. The maximum tractive force that can be applied is determined by the adhesive force due to the vacuum in the cup and by the matching fit between the instrument and the head deformation cause by the vacuum. Since breakaway of the cup from the scalp can lead to injury to the baby, the criteria for premature breakaway have been investigated. Two measuring disks fitted with strain-gage diaphragm rosettes were mounted in a suction cup for measuring the subpressure and the tractive force applied to the baby's head.