First and Second Stage Risk Factors Associated with Perineal Lacerations.

Objective: To determine intrapartum factors associated with perineal laceration at delivery.

Methods: This was a planned secondary analysis of a multicenter randomized clinical trial of delayed versus immediate pushing among term nulliparous women in labor with neuraxial analgesia conducted in the United States. Intrapartum characteristics were extracted from the medical charts. The primary outcome was perineal laceration, defined as second degree or above, characterized at delivery in women participating in longer term pelvic floor assessments post-delivery. Multivariable logistic regression was used to refine risk estimates while adjusting for randomization group, birth weight, and maternal age.

Results: Among the 941 women participating in the pelvic floor follow-up, 40.6% experienced a perineal laceration. No first stage labor characteristics were associated with perineal laceration, including type of labor or length of first stage. Receiving an amnioinfusion appeared protective of perineal laceration (adjusted odds ratio, 0.48; 95% confidence interval 0.26-0.91; P = 0.01). Second stage labor characteristics associated with injury were length of stage (2.01 h vs. 1.50 h; adjusted odds ratio, 1.36; 95% confidence interval 1.18-1.57; P < 0.01) and a prolonged second stage (adjusted odds ratio, 1.64; 95% confidence interval 1.06-2.56; P < 0.01). Operative vaginal delivery was strongly associated with perineal laceration (adjusted odds ratio, 3.57; 95% confidence interval 1.85-6.90; P < 0.01).

Conclusion: Operative vaginal delivery is a modifiable risk factor associated with an increased risk of perineal laceration. Amnioinfusion appeared protective against injury, which could reflect a spurious finding, but may also represent true risk reduction similar to the mechanism of warm perineal compress.