Preconceptional counselling of women with previous third- and fourth-degree perineal tears
Reports show that approximately 85% of women undergo perineal trauma during the second stage of labour, with 1.5% of those reported as third- or fourth-degree perineal tears (109).
Perineal tears are classified as first, second, third, or fourth degree, depending on the anatomical depth of the tear. First- and second-degree tears involve the depth of the skin, and perineal muscles, respectively, with no involvement of the anal sphincter (110). When the anal sphincter is involved, this is considered a third-degree tear, with three levels of depth of involvement: 3a, less than 50% thickness of the external anal sphincter; 3b, more than 50% thickness of the external anal sphincter; and 3c, involvement extends to the internal anal sphincter (110). Fourth-degree tears penetrate to the depth of the anal mucosal layer, and are the most severe form of perineal tears (110). Classification of anal sphincter involvement, as in third- and fourth-degree tears, is classified as obstetrical anal sphincter injuries (OASIS), and can have significant morbidity for women, including perineal pain, dyspareunia, and anal incontinence (111, 112). The additional psychological impact should not be underestimated, as this can play a major role in preventing women from seeking medical attention for these symptoms (112).During preconceptional counselling of women with previous OASIS, the risk factors should be discussed, both for future management decisions and to identify any modifiable risk factors that may be present. Obstetrical risk factors for OASIS include macrosomia (>4500 g), operative vaginal delivery with forceps or vacuum assistance, and midline episiotomy, but not mediolateral episiotomy (113). Women with previous OASIS should be counselled regarding the modifiable risk factors if vaginal birth is planned, including location of episiotomy if indicated at the time.
There is evidence to show that the fetal head position can affect the relative risk of OASIS, with occiput posterior position causing a sevenfold increase in the incidence of OASIS in one study (114). Unfortunately there is no conclusive evidence to recommend specific birthing positions or delayed second-stage pushing to influence the rate of third- and fourth-degree perineal tears.Due to the physical and emotional trauma surrounding OASIS for many women, one of the pertinent questions to be addressed in the preconceptional period following previous third- and fourth-degree tears is the mode of delivery for a subsequent pregnancy. Evaluation of the risk of recurrence is an important factor to consider, as well as the emotional trauma surrounding the woman's previous experience. Studies have shown that there is an increased risk of subsequent sphincter laceration for woman with previous OASIS who deliver vaginally (115, 116). Specific risk factors for recurrent OASIS have been identified, including Asian ethnicity, forceps delivery, and birthweight more than 4 kg (110). For this reason, many women request an elective caesarean delivery, with evidence that shows even obstetricians themselves demonstrate a bias to choose elective caesarean with the primary reason being the potential risk of perineal trauma (117, 118).