The vacuum extractor was the first instrument to be used in 79% and 87% of the instrumental deliveries in groups A and B, respectively, with corresponding failure rates of 20% and 21%. Although an occipito-posterior position was diagnosed in 11% of cases of group A and 14% of cases of group B, the specifically designed occipito-posterior cup was not used at all. The vacuum cup was considered to have been applied suboptimally in 40% of the cases where attempted vacuum delivery failed.