E. Baghestan et al. reported that the risk of anal sphincter injury was increased in women whose mother or sister had suffered from a sphincter injury during delivery.
However, this study missed several important factors involved in anal sphincter tears, e.g. mode of delivery and the anatomy of the ano-vulvar region of women. Indeed, instrumental delivery, especially with forceps, increases significantly the rate of anal sphincter injury.[2, 3] Unfortunately, we do not have information on the types of instrument (forceps, vacuum extractor) used during the deliveries in this study.
A short ano-vulvar distance in women also increases the risk of anal injury during delivery. The ano-vulvar distance was not reported in this study.
Moreover, the technique of episiotomy was not described, even though midline episiotomies are more often complicated by anal sphincter tears than are mediolateral episiotomies.
In addition, no information was provided on the percentage of anal sphincter lacerations in the maternity units in which the patient and her mother or sister were delivered. Indeed, the incidence of anal sphincter tears is widely dependent on the obstetric practice.
All of these missed factors introduce bias and make the conclusions of the authors less convincing. Although a familial risk of anal injury should be considered, the mode of delivery and the anatomy of the ano-vulvar region are of primary importance in the avoidance of anal sphincter tears.