In the large and interesting study by Bultez et al., including 235 women who underwent vacuum delivery, the relationship between measurement of the angle of progression (AoP, assessed by transperineal ultrasound just prior to instrument application) and the vacuum extraction failure rate was investigated. In the 30 (13%) women experiencing vacuum failure, compared with the 205 who had a successful procedure, the authors found a significantly smaller AoP (136.6° vs 145.9°), whereas, surprisingly, the median fetal head station established at clinical examination did not vary between the two groups (+2 cm in both). In this study, unlike previous ones, 46 fetuses with persistent occiput posterior or occiput transverse position prior to vacuum delivery (and confirmed by transabdominal ultrasound) were also included and, unexpectedly, the rate of vacuum extraction failure was not significantly different between these and the occiput anterior (OA) fetuses. However, while in the OA group the AoP was smaller among cases with failed procedures, in the non-OA fetuses the angle of progression did not vary in accordance with the outcome of instrumental delivery.