Abstract: We included 32 studies (6597 women) in this review. Forceps were less likely than the ventouse to fail to achieve a vaginal birth with the allocated instrument (risk ratio (RR) 0.65, 95% confidence interval (CI) 0.45 to 0.94). However, with forceps there was a trend to more caesarean sections, and significantly more third- or fourth-degree tears (with or without episiotomy), vaginal trauma, use of general anaesthesia, and flatus incontinence or altered continence. Facial injury was more likely with forceps (RR 5.10, 95% CI 1.12 to 23.25). Using a random-effects model because of heterogeneity between studies, there was a trend towards fewer cases of cephalhaematoma with forceps (average RR 0.64, 95% CI 0.37 to 1.11). Among different types of ventouse, the metal cup was more likely to result in a successful vaginal birth than the soft cup, with more cases of scalp injury and cephalhaematoma. The hand-held ventouse was associated with more failures than the metal ventouse, and a trend to fewer than the soft ventouse. Overall forceps or the metal cup appear to be most effective at achieving a vaginal birth, but with increased risk of maternal trauma with forceps and neonatal trauma with the metal cup. There is a recognised place for forceps and all types of ventouse in clinical practice. The role of operator training with any choice of instrument must be emphasised. The increasing risks of failed delivery with the chosen instrument from forceps to metal cup to hand-held to soft cup vacuum, and trade-offs between risks of maternal and neonatal trauma identified in this review need to be considered when choosing an instrument.

Plain-language summary: This review of 32 studies (6597 women) looks at assisted or instrumental vaginal deliveries in women in the second stage of labour. The importance of this review is due to the fact that Instrumental delivery is a frequent intervention in childbirth and in some cases may result in harmful outcomes for either mother or baby or both. The main comparisons are between the forceps or the ventouse. There are also comparisons between different types of ventouse. The outcomes which are analysed are the success of the particular instrument in achieving the delivery and the rate of complications for both mother and baby. Not all studies considered all outcomes, and in particular, there were differences in the types of complications encountered by mothers and babies. In addition, we identified no studies for some comparisons. The results showed that the forceps was the better instrument in terms of achieving a successful delivery. However, it was also associated with higher rates of complications for the mother. These were perineal trauma, tears, requirements for pain relief and incontinence. There were risks of injury to the baby with both types of instrument. Comparisons between different types of ventouse revealed that the metal cup was better at achieving successful delivery than the soft cup,.but with more risk of injury to the baby. There were no significant differences between the handheld and the standard vacuum. Decisions as to which instrument is best will, therefore, depend upon individual situations where the urgency with which the baby needs to be delivered will be balanced against potential risks to the mother and baby.