Vacuum extraction: a randomized controlled comparison of the New Generation cup with the original BIRD cup

Abstract

A new design of vacuum extractor cup - ''the New Generation cup'' - has recently been introduced into clinical practice. Its major modification is a traction cord which passes around the rim of the cup for 180.degree. and is free to slide within the rim. Claims that this design ''enables the operator to pull obliquely without causing the cup to tilt'' and thereby ''reduces failure rates, reduces the incidence of scalp trauma and increases operator confidence'' have been evaluated in a randomized controlled trial. 123 women with singleton pregnancies of 37 completed weeks or more, with a cephalic presentation and for whom a decision to deliver by vacuum extraction had been taken, were randomly allocated to the ''New Generation'' cup or Bird''s original vacuum extractor cup; 50 mm anterior and posterior cups were used in both groups as appropriate. The two groups were comparable at entry and delivered by obstetricians of similar status (table I). The two types of cup were similar in respect of number of failures to deliver with the vaccum extractor (table II), correct positioning of the cup, number of pulls required for delivery and time taken to expedite delivery. Cup detachments occurred in nine cases allocated to the ''New Generation'' cup compared with four allocated to the original Bird cup. The babies in the two groups were in similar condition at birth (table IV) and sustained similar amounts of scalp trauma (table III). Neonatal jaundice, both clinical (table IV) and biochemical, was more common in babies delivered with the ''New Generation cup'' and this was reflected in greater use of phototherapy in this group. Operators were equally divided in their preference of cup. This study provides little evidence that the use of the ''New Generation'' cup is associated with a reduction in cup detachment and scalp trauma and an increase in operator confidence. These estimates, although unbiased, are, however, imprecise because of the size of the trial and ideally further randomized controlled comparisons are required to reduce imprecision. Nevertheless, on the basis of this study, the relative advantages and disadvantages of the two types of vacuum extractor cup appear to be small.