Episiotomy to prevent obstetric anal sphincter injuries during instrumental delivery in nulliparous women: a national prospective comparative cohort study

Abstract

Background: We are lacking data with a high level of evidence on the use of episiotomy during instrumental delivery to prevent anal sphincter injury, which nonetheless presents the highest risk.

Objective: Our main objective was to assess the protective effect of episiotomy against obstetric anal sphincter injury in nulliparous women during instrumental delivery according to type of instrument. We also investigated its impact on immediate maternal and neonatal morbidity.

Study design: We conducted a prospective comparative cohort study for clinical trial emulation by means of propensity score weighting. The study was especially designed for consideration of possible confounders. This was a nationwide observational multicenter study including 111 French public and private maternity units between April 2021 and March 2022. We included nulliparous women, with singleton cephalic fetus, at more than 34 weeks of gestation. We considered vacuum, forceps, and spatula deliveries. We proceeded to a comparative analysis between women with and without episiotomy. The main outcome was obstetric anal sphincter injury occurrence. We used composite criteria for both maternal and neonatal immediate morbidity.

Results: The analyses pertained to 11,013 women. Overall prevalence of episiotomy was 23%: 17% for vacuum (N=7007), 37% for forceps (N=2378), and 29% in case of spatula-assisted (N=1628) delivery. Episiotomy was not associated with significantly decreased obstetric anal sphincter injury occurrence in vacuum delivery (from 5.2% without episiotomy to 3.8%, odds ratio=0.73 [0.48-1.03]) or forceps delivery (from 10.9% without episiotomy to 8.8%, odds ratio=0.81 [0.56-1.14]). In contrast, we observed significantly decreased obstetric anal sphincter injury occurrence (from 9.4% without episiotomy to 5.6%) in spatula delivery (odds ratio=0.60 [0.37-0.87]). Episiotomy was associated with increased maternal morbidity using forceps (from 13.6%-18.3%, odds ratio=1.35 [1.01-1.73]) and spatulas (from 9.0%-13.4%, odds ratio=1.51 [1.11-2.00]). We also observed increased neonatal morbidity in vacuum delivery associated with episiotomy (from 9.1%-13.6%, odds ratio=1.49 [1.21-1.79]), but a decrease in case of forceps delivery with episiotomy (from 12.6%-9.2%, odds ratio=0.74 [0.55-0.95]).

Conclusion: Episiotomy was not associated with a decreased risk of obstetric anal sphincter injury in vacuum or forceps delivery, and a marginal reduction was achieved using spatulas. Our results do not favor extensive episiotomy during instrumental delivery.

Trial registration: ClinicalTrial NCT04446780.

Keywords: cohort; episiotomy; instrumental delivery; obstetric anal sphincter injury; propensity score.