(664) The association of maternal obesity and fourth-degree perineal laceration at time of vaginal delivery

Objective: The risk of fourth-degree laceration in obesity is relatively understudied and has mixed findings in existing literature. This study examined the association of obesity and fourth-degree laceration following vaginal delivery.

Study Design:
The National Inpatient Sample was retrospectively queried to examine 7,385,341 vaginal deliveries from 1/2017-12/2019. Exposure assignment was obesity status (n=657,590). Main outcomes included third and fourth-degree lacerations. A confounder-mediator analysis was fitted to examine the exposure-outcome association: (i) inverse probability of treatment weighting (IPTW) with log-Poisson regression generalized linear model to account for pre-pregnant and pregnant confounders for the exposure (25 factors); and (ii) multinomial regression model to account for mediators at delivery in the IPTW cohort (10 factors). Secondary outcome included the trend of fourth-degree laceration.


Results: In the IPTW cohort, obese patients were less likely to have fourth-degree lacerations (0.2% vs 0.4%, adjusted-odds ratio [aOR] 0.64, 95% confidence interval [CI] 0.58-0.71) and third-degree lacerations (1.6% vs 2.0%, aOR 0.81, 95%CI 0.78-0.84) compared to non-obese patients. Forceps delivery (5.5% vs 0.3%, aOR 17.92, 95%CI 16.34-19.64), vacuum delivery (2.0% vs 0.3%, aOR 5.20, 95%CI 4.87-5.56), episiotomy (1.9% vs 0.3%, aOR 3.95, 95%CI 3.72-4.20), and shoulder dystocia (1.8% vs 0.3%, aOR 2.64, 95%CI 2.33-2.98) were associated with significantly increased risk of fourth-degree laceration. The incidence of fourth-degree laceration decreased by 10.1% during the study period, while forceps delivery, vacuum delivery, and episiotomy decreased by 4.7%, 2.3%, and 23.6% respectively (all, P< 0.001).

Conclusion:
This contemporaneous national-level analysis suggests that obese patients are less likely to have a fourth-degree laceration while confirming the risk factors associated with fourth-degree laceration. It also showed an overall decreasing trend in fourth-degree lacerations which may be due to the decreasing trends of risk factors.