The paper by de Leeuw et al. determines risk factors for injury to the anal sphincter at delivery1. This paper can throw further light on two common clinical questions: is vacuum extraction preferable to a forceps delivery and is an episotomy always indicated?
Guidelines published by the Royal College of Obstetricians and Gynaecologists suggest vacuum extraction as the instrument of choice due to a decrease in maternal injuries2 and this would appear to be confirmed by this paper. Data in de Leeuw et al.'s paper show an unadjusted relative risk of 1.87 for those deliveries started with vacuum extraction (i.e. all those delivered with vacuum and those where vacuum failed and forceps were used in addition). In this group, the use of forceps in addition to vacuum extraction was necessary in 8%, in keeping with other studies.
Unlike the findings of a Cochrane review3, this paper suggests that episotomy is an independent protective factor for third degree tears. If this is true, then assisted deliveries should include an episotomy. This will cancel to some degree one advantage of vacuum extraction, that episotomy may be avoided.
Two factors may however throw doubt on these findings. Firstly, rotational deliveries are not described separately and so it is impossibly to compare non-rotational forceps vs vacuum deliveries. Secondly, all gestational ages over 16 weeks are included and no data are given regarding the gestational age at delivery, which is a possible confounding factor. Was gestational age at delivery a risk factor for assisted vaginal delivery or third degree tears?