Perineal stress as a predictor of performing episiotomy in primiparous women: a prospective observational study

BACKGROUND: Episiotomy is a surgical solution to relieve perineal stress, resulting in an easily repairable incision, in comparison to the risks of serious vaginal trauma during delivery. The midwife typically adopts such a clinical decision, on experience and subjective judgment. However, the association between perineal stress and episiotomy is poorly characterized. Our aim was to identify a threshold value for perineal stress leading to episiotomy, which eventually may be employed as a clinical tool for assessing whether an episiotomy is required or not. METHODS: In total, 245 nulliparous women were investigated for perineal stress during non-instrumental vaginal delivery in Ningbo Women & Children’s Hospital. During the second stage of labor, a flexible membrane stress sensor was placed between the fetal head and perineal wall above the anal fissure. Once the entire fetal head pressed against the sensor, real-time perineal stress was measured, and the peak value was recorded. Cases were divided into non-episiotomy group (n = 173) and episiotomy group (n = 72). The correlations between perineal stress and episiotomy was assessed through logistic regression with adjustment for maternal age, estimated birthweight, duration of second stage of labor, maternal body mass index, and presence of analgesia. Midwives were blinded to all stress measurement values. The predictive value of perineal stress on performing episiotomy was evaluated, together with the ideal cut-off perineal stress value for performing episiotomy. A ROC analysis was also performed. RESULTS: The episiotomy group had significantly higher levels of perineal stress in comparison to the non-episiotomy group (140.50 ± 16.03 N versus 118.37 ± 19.21 N, p < 0.01). The episiotomy group was linked to significantly higher perineal stress in comparison to the non-episiotomy group (140.50 ± 16.03 VS 118.37 ± 19.21 N, p < 0.01). ROC analysis between perineal stress and episiotomy revealed a high area under the curve (AUC 0.81, 95% CI 0.75–0.86) and a cut-off value for perineal stress of 124.49 N was identified for episiotomy decision. CONCLUSION: The level of perineal stress was an independent predictor of performing episiotomy in nulliparous women during non-instrumental vaginal delivery. Perineal stress exceeding 124.49 N was identified as the cut-off prompting midwives to perform episiotomy.