(1099) Anal sphincter injury after vacuum-assisted delivery- is avoiding episiotomy still safe?

To assess whether avoiding episiotomy during vacuum-assisted deliveries (VAD) affects the incidence of anal sphincter injury (OASI) in primiparous women.

Study Design: A retrospective cohort study of all primiparous patients who had a VAD at a university-affiliated tertiary center (2011-2022). In our institution, during VAD, a mediolateral episiotomy is performed at the attending physician's discretion. We compared outcomes between VADs with and without episiotomy. Baseline characteristics were evaluated along with various VAD parameters. The primary outcome was OASI, with secondary outcomes including other maternal adverse events.

Results:

Out of 157,282 deliveries, 10,400 (6.6%) were VADs, and 7,951 met the inclusion criteria. Among these, 7,201 (90.6%) had episiotomies, and 750 (9.4%) did not. Baseline maternal characteristics were similar between the groups. Those who had episiotomy had a higher rate of prolonged second stage of labor (PSS) (32% vs. 25.9%, p=0.001), higher rates of occipitoposterior position (OP) (18.6% vs. 14.3%, p=0.016) and more advanced head station (+3 under ischial spine in 5.3% vs. 9.3%, p< 0.001), as compared to no episiotomy. Newborns weighing >3500 grams were more common in the episiotomy group (25.4% vs. 21.7%, p=0.027).

Despite these known risk factors for OASI, the incidence of OASI was higher in the no-episiotomy group (2.8% vs. 1.4%, p=0.004). Multivariable analysis confirmed that episiotomy had a protective effect against OASI [aOR 0.433 (0.258-0.728), p=0.002]. Prolonged second stage [aOR 1.98 (1.32-2.94), p< 0.001] and higher birthweight [aOR 1.86 (1.09-3.17), p=0.022] also correlated with a higher risk of OASI. The number needed to treat (NNT) to prevent one OASI with episiotomy was 71, reduced to 42 for PSS, 33 for OP, and 22 for newborns >3500 g. Other maternal adverse outcomes were similar, except for a higher postpartum blood transfusion rate in the episiotomy group (3.9% vs. 1.5%, p=0.008).

Conclusion:

Avoiding routine episiotomy during VAD in primiparous women is associated with a higher OASI rate, particularly in those with PSS, OP, or larger newborns.