[Is primiparity, the only risk factor for type 3 and 4 perineal injury, during delivery?]

Primiparity has been identified as the main risk factor of type 3 and 4 perineal injuries The purpose of our study, according to a population-based observational study, was to identify other clinical risk factors for lesions during vaginal delivery.

Two groups have been compared. Group A or study group (n=63) was defined as parturients with three or four-degree perineal tears. Group B or control group (n=67) included women who delivered vaginally without any perineal lesion during the same period. Characteristics of the population were compared: maternal age, race, maternal weight, BMI (Body Mass Index), parity, mode of anaesthesia, gestational age, post maturity, length of labor, fetal weight, mode of delivery (assisted or not). Specific characteristics were also compared, obesity, shoulder dystocia, type of presentation, episiotomy and dose of ocytocin.

Primiparity was significantly associated with higher frequency of sphincter lacerations (71 vs 43%, p=0.001). The patients of group A were with significantly higher weight than the patients of control group (67 vs 63 kg, p=0.036). Futhermore the BMI was different in the two groups (25,6 vs 23,4, p=0.003). There was a significant difference according to the length of the second part of labor (68 vs 48 min, p=0.037) and the posterior variety (32 vs 4%, p<0.001). The occurrence of shoulder dystocia was only just significant (6 vs 0%, p=0.052). Assisted-extraction is highly associated with perineal injuries (44 vs 1%, p<0.001). Futhermore the instrument has been concerned by the difference: Tarnier's forceps-assisted extraction (14 vs 1%, p=0.003), Suzor's forceps-assisted extraction (16 vs 0%, p=0.0005), Thierry's spatula-assisted extraction (14 vs 0%, p=0,0005). The association forceps and episiotomy has been found with higher frequency of perineal injury (43 vs 1%, p<0,0001). There were no difference between the 2 groups according fetal characteristics, type of analgesia, maternal age, gestational age, post-maturity or dose of ocytocin.

Primiparity is not the only risk factor of perineal injuries. Other risk factors have been found: assisted-extraction, occiput posterior fetal head position, and association episiotomy and assisted-extraction. Black origin seems to be protective.