Data collection
Data were collected prospectively. For each woman included, we collected data on the following: the final mode of delivery (success or failure of the vacuum attempt), the values of the fifteen potential risk factors previously described, the type of room where the VAD was attempted, the neonatal outcomes (five-minute Apgar score, arterial umbilical cord blood pH, immediate neonatal resuscitation, neonatal transfer location), the maternal outcomes (perineal trauma, quantity of blood loss) and whether the preparation of the C-section equipment had been anticipated. In cases of C-section, we also collected data on whether the extension of epidural anaesthesia had been anticipated, whether general anaesthesia had been required, and the durations between the C-section decision, skin incision and birth.
Fundal height was measured by the midwife at admission to the labour room (regardless of a potential rupture of membranes). Cervical dilation was evaluated by the midwife by digital vaginal examination every hour during labour. The fetal head position at the beginning of the VAD was evaluated by digital vaginal examination and transabdominal ultrasound. The fetal head station at the beginning of the VAD was evaluated by the head-perineum distance measured by trans-perineal ultrasound, according to the method described by D. Maticot-Baptista et al. and the IUSOG: outside of uterine contraction and without compression of the soft tissue against the pubic bone 20,21. The presence of a caput succedaneum was subjectively evaluated by the obstetrician by digital vaginal examination and trans-perineal ultrasound, with three possible outcomes: absent or insignificant/medium sized/bulky. The perineal trauma was evaluated by the obstetrician according to the RCOG classification of perineal tears. Immediate neonatal resuscitation corresponded to new-borns for whom one or more of the following actions were required: non-invasive or invasive ventilation (with face mask, nasal cannula, or endotracheal intubation), chest compressions, umbilical cord vein catheter insertion, or intravenous administration of epinephrine.