OBJECTIVE:

To estimate the association between non-interventional delivery and the risk of obstetric anal sphincter injuries.

MATERIALS AND METHODS:

Case-control, observational, longitudinal, retrospective, and analytical study performed in patients attended between 2016 and 2019 at Hospital Ángeles Lomas, with term pregnancy who had non-interventional delivery. Dependent variables: third- and fourth-degree perineal tears, dilation at admission, labor hours and episiotomy. Independent variables: age, body mass index, pregnancies, deliveries, and newborn weight. Comparison of outcomes with a control group with interventional delivery. Tears were categorized using the Sultan classification. Patients with multiple pregnancy, preterm or instrumented delivery were excluded.

RESULTS:

A total of 253 non-intervened and 253 intervened deliveries were attended. Obstetric anal sphincter injury was present in 2.4% of patients with non-intervened delivery and in 4.0% without intervened delivery (RR: 1.66; 95%CI: 0.61-4.51). Labor was 3.50 hours in patients with non-intervened delivery and 4.41 hours in the control group. Episiotomy was performed in 22.9% of women with non-intervened delivery and in 44.3% of the control group (RR: 1.93; 95%CI: 1.48-2.51).

CONCLUSIONS:

Women with non-intervened delivery had no increased risk of third- or fourth-degree perineal tear. In those who had an interventional delivery, the risk of requiring episiotomy was higher.

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