Labour Curve Findings Associated With Fourth Degree Sphincter Disruption: The Impact of Labour Progression on Perineal Trauma

Objectives: To compare the labour curves of primigravid women with fourth degree perineal laceration with those of control subjects, and to identify characteristics of the labour curve that are associated with anal sphincter disruption. Methods: In this retrospective case-control study we constructed labour curves describing the mean cervical dilation and head descent for 72 primigravidas with fourth degree laceration and compared these with the labour curves of 72 consecutive primigravidas having a vaginal delivery without sphincter laceration. Results: The control cervical dilatation curve resembled the Friedman labour curve, consisting of an acceleration phase, a phase of maximal slope, and a deceleration phase. In contrast, the dilatation curve of the laceration group was longer and had an increasing rate of dilatation without a deceleration phase. While the rate of head descent progressively decreased in the control group, it accelerated in the laceration group. Conclusion: Labour curves for the sphincter laceration and control groups were different. Increasing rates of cervical dilatation and head descent were associated with fourth degree perineal laceration.