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The risk of obstetric anal sphincter injury (OASIS) is increased in vacuum-assisted delivery. However, it remains unclear whether episiotomy may protect against OASIS in this type of delivery. The objective of this study was to assess whether mediolateral or lateral episiotomy affects the risk of OASIS in vacuum assisted delivery among primiparous women.

Data were found searching The PubMed, Cochrane library and Embase databases electronically. Studies investigating the risk of OASIS in vacuum-assisted delivery with and without the use of mediolateral or lateral episiotomy were considered for inclusion. Of the 452 studies found, 15 observational studies were included in this meta-analysis. All authors assessed risk of bias of the included studies using the Scottish Intercollegiate Guideline Network (SIGN) quality score.

According to this meta-analysis, mediolateral or lateral episiotomy significantly reduced the risk of OASIS in vacuum-assisted deliveries in primiparous women (OR 0.53 (95% CI 0.37-0.77)). Numbers needed to treat (NNT) was 18.3 (95% CI 17.7-18.9). The protective effect of episiotomy seemed most pronounced when performed in more than 75% of vacuum-assisted deliveries (OR 0.37 (95% CI 0.150.92)).

In conclusion, this meta-analysis showed that mediolateral or lateral episiotomy was protective against OASIS and may be considered in vacuum-assisted delivery in primiparous women. Randomized controlled trials to further investigate this finding are warranted. (C) 2016 Elsevier Ireland Ltd. All rights reserved.