Behavior of perineum during delivery before fetal head expulsion

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.

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.

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.

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.