OBJETIVE:

to determinate the risk factors of intrapartum anal sphincter tear.

MATERIAL AND METHOD:

a retrospective case-control study which included a total of 97 patientes: 48 with anal sphincter tear and 49 without tear.

RESULTS:

There was an incidence of 1.6% of anal sphincter injury (1.3% in primiparous and 0.3% in multiparous). In bivariate analysis statistical significant differences was found in primiparity (p=0.003), labour induction (p<0.001), instrumental delivery (p=0.006), dilatation duration (p=0.023), duration of expulsive stage (p=0.007), episiotomy (p<0.001), fetal weight (p=0.006) and urinary incontinence (p=0.002). Univariate analysis showed a statistical difference in primiparous (OR 3.833, p=0.004), instrumental delivery (OR 3.214, p=0.007), episiotomy (OR 6.101, p<0.001), fetal weight (OR 1.001 for each grams, p=0.009), dilatation duration (OR 1.004 for each minute, p=0.012), duration of expulsive stage (OR 1.007 for each minute, p=0.016). In the multivariate analysis significant difference was found in episiotomy with an OR=6.76 and CI 95% of 2.436-18.805, and fetal weight with an OR=1.001 and CI 95% of 1.000-1.002; the discrimination index area under the curve (AUC) showed a value of 0.762, CI=0.667-0.856.

CONCLUSIONS:

the anal sphincter injury is multifactorial and difficult to predict. Intervention on modifiable risk factors should allow a reduction in its incidence.

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