Behavior of perineum during delivery before fetal head expulsion

Abstract

Introduction and hypothesis

The aim of this study was to describe perineum deformation during the final part of delivery and suggest a modification of the episiotomy cut to increase accuracy for obtaining a suitable angle (45°) for surgical wound suture.

Methods

This prospective study enrolled 45 primiparous women. The perineum at rest was marked with five lines (0°, 30°, 45°, 60°, 90°), and each line was marked with two dots (point A–B: to 2–3 cm from initial point in fourchette, respectively). Two digital pictures were taken: one with the women at rest and the second during fetal head crowning; displacements were calculated for each point and angle.

Results

When the perineum is distending, the initial point of every line in the posterior fourchette moves laterally in introitus (only the 0° line remains at midline). The angle and the distance to points A and B of each line drawn do not change significantly from at rest to crowning. However, comparing original line configuration with an imaginary line from the fourchette to points A and B before expulsion, the angle and the distance is increased statistically significantly.

Conclusions

Perineal distension at the moment of fetal head crowning causes a linear displacement of the perineum, which causes the difference in angle between the incision and episiotomy suture. Therefore, to obtain an episiotomy suture from fourchette with an angle of 45°, theoretically, we would have several angle incision options (between 45° and 60°), with a less acute angle when the introitus cut is closer to the fourchette (45° to 6 mm and ∼60° in the fourchette) and a sharper angle with a longer episiotomy.