Risk factors for severe perineal injury during childbirth: a case-control study of 60 consecutive cases

AIM: The study aimed to evaluate the current risk factors for severe perineal tears in a single university-affiliated maternity hospital. METHOD: An obstetric database of 31 784 consecutive women who delivered from January 2007 to December 2009 was screened for cases of third-degree or fourth-degree perineal tears. Four controls, matched by time of delivery, were selected for each case of third- or fourth-degree perineal tear. Maternal and obstetric parameters were analyzed and compared between the study and control groups. RESULTS: Sixty women (0.25% of all vaginal deliveries) had a third-degree (53 women) or a fourth-degree (seven women) perineal tear. The control group comprised 240 matched vaginal deliveries without severe tears. Primiparity, younger maternal age, Asian ethnicity, longer duration of second stage of labour, vacuum-assisted delivery and heavier newborn birth weight were significantly more common among women who had third- or fourth-degree perineal tears. Of the variables that were found to be statistically significant in the univariate analysis, only primiparity (OR = 2.809, 95% CI: 1.336-5.905), vacuum delivery (OR = 10.104, 95% CI: 3.542-28.827) and heavier newborn birth weight (OR = 1.002, 95% CI: 1.001-1.003) were found to be statistically significant independent risk factors for severe perineal trauma. CONCLUSION: Identification of women at risk may facilitate the use, or avoidance, of certain obstetric interventions to minimize the occurrence of childbirth-associated perineal trauma.