Reducing Obstetric Anal Sphincter Injuries in Instrumental Vaginal Deliveries

Obstetric anal sphincter injuries (OASIS), encompassing third- and fourth-degree perineal lacerations, remain a significant concern in vaginal deliveries, particularly those involving instrumental assistance. These injuries are not only painful but are also associated with long-term complications, even after surgical repair. Studies indicate that 30-70% of women who suffer OASIS during vaginal delivery experience anal incontinence. Additionally, there also may be persistent dyspareunia, perineal pain, post-traumatic stress disorder, and overall reduced quality of life, highlighting the profound impact of these injuries on women's health.

The prevalence of OASIS is notably higher in forceps-assisted deliveries compared to vacuum-assisted ones, indicating the need for careful consideration when choosing the type of instrumental intervention. The experience in Norway offers valuable insights into mitigating this risk. Following the introduction of a national care bundle in 2005, which emphasized manual perineal protection, selective episiotomy based on clinical indication, and effective communication with the woman during delivery (including instructing her not to push during crowning), there has been a marked reduction in OASIS rates. 

Evidence also supports the protective role of mediolateral and lateral episiotomy techniques against OASIS in both vacuum and forceps deliveries. In contrast, median episiotomy has been shown to increase the risk of these injuries. 

Given these findings, it is reasonable to advocate for a preference for vacuum over forceps delivery, coupled with using mediolateral or lateral episiotomy in appropriate clinical settings. Such an approach could significantly lower the risk of OASIS, especially in nulliparous women. By learning with the latest evidence, we can continue to improve maternal outcomes and reduce the burden of preventable childbirth-related injuries.

Fodstad K, Laine K, Räisänen S. Obstetric anal sphincter injuries during instrumental vaginal delivery: An observational study based on 18-years of real-world data. BJOG: An International Journal of Obstetrics & Gynaecology. https://doi.org/10.1111/1471-0528.17914