mechanism of labour

Mechanism of labor

Mechanism of labor, or the cardinal movements of labor, refer to the changes in position of the fetal head during passage through the birth canal in the vertex presentation
1- Engagement
This usually occurs late in pregnancy in the primigravida, commonly in the last 2 weeks. In the multiparous patient, engagement usually occurs with the onset of labor. Engagement is descent of the biparietal diameter of the fetal head below the plane of the pelvic inlet.

2- Descent
uterine activity causes the fetal head to descend through the pelvic brim to the midcavity.

3- Flexion
Uterine activity is fundally dominant; the line of force is down the fetal spine and causes flexion of the fetal head. flexion is a passive movement that permits the smallest diameter of the fetal head (suboccipitobregmatic diameter) to be presented to the maternal pelvis.
4- Internal rotation
The head rotates from the right occipitotransverse position at engagement to become direct occipitoanterior
5- Extension
As the head continues its descent, gradual extension of the fetal head occurs distending the perineum. With more extension, the widest diameter passes through the vulval introitus (crowning) and the head is born by extension at the fetal neck.

6- Restitution and external rotation of the head


7- Delivery of the body
Delivery of the anterior shoulder is aided by gentle downward traction on head. The posterior shoulder is then delivered by gentle upward traction on the head. Following these maneuvers, the body, legs, and feet are delivered with gentle traction on the shoulders.