The importance of flexion in vacuum extractor delivery.

Two modifications of Malmstrom's cup were used in a study of the position of the cup in 500 vacuum extractor deliveries. The incidence of completely flexing applications varied from 0 to 92 per cent according to the level of the head and the position of the occiput when the cup was applied and, in occipito-posterior positions, the type of cup that was used. With mid-cavity occipito-posterior positions it was 30 per cent with one modification (suction tube attached eccentrically to the dome of the cup--the "modified" cup) and 92 per cent with the other (tube attached to the lateral wall of the cup--the "occipito-posterior cup" or "OP cup"). The high incidence of face-to-pubis or occipitio-lateral delivery when cups with a dome-attached suction tube were used in mid-cavity occipito-posterior positions was found to be largely the result of deflexing applications. It was concluded that cups of this type are unsuitable for use in these cases. A study of two large series of vacuum extractor operations suggested that failed vacuum extractor rates can be reduced by using cups that are manoeuvreable and which accept stronger oblique traction than Malmstrom's cup.