mechanism of labour

mechanism of labour
Mechanisms 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
Engagement is descent of the biparietal diameter of the fetal head below the plane of the pelvic inlet.
The head enters the pelvis in the occiput transverse position in women with a gynecoid pelvis.
2nd step
descent
flexion
internal rotation
extension
external rotation
expulsion
during descent of fetal head it will rotate from the left occipitotransverse position at engagement to become direct occipitoanterior.
Further descent through the pelvis causes the chin to be forced tightly up against the fetal chest. The fetal occiput comes to lie behind the maternal symphysis pubis.
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.