Mechanism of labour
A series of changes in position and attitude the fetus undergo during its passage through the birth canal.
Vertex presentation fetus in gynecoid pelvis
Terminology
1. Lie
Longitudinal lie
Transverse lie
Oblique lie
2. Attitude
Posture of fetus
Head flexed over chest
Arms/Hands flexed over chest
Thigh/ legs flexed over abdomen
3. Presentation
Portion of the body of fetus.
Vertex, breech, face, eyebrow, shoulder
4. Position
Fetal presenting part right to left side of maternal birth canal.
5. Denominator
Bony landmark of presenting part, used to describe postion of presentation.
In vertex; occiput
In face; mentum(chin)
In breech; sacrum
In shoulder; scapula
Cardinal movements of labour
Mechanism of labour (9 movements)
1. Engagement
2. Descent
3. Flexion
4. Internal rotation of head
5. Crowning
6. Extension
7. Restitution
8. External rotation of head/ internal rotation of shoulder
9. Lateral flexion of body and shoulder through birth canal
1. Engagement
Biparietal diameter of fetal head passed through pelvic inlet.
In primigrivida; usually occurs 12 hours
In multigravidae; occurs within 6 hours
2. Descent
Contraction, maternal pushing effort with contraction of her abdominal muscles.
Baby descents through pelvic inlet towards the pelvic floor.
3. Flexion
Increase flexion of head.
Fetal head come contact with pelvic floor. Allow presenting part of fetus to be sub- occipital bregmatic.
In this position, fetal skull has smallest diameter which assists passage through pelvis.
4. Internal rotation of head
Internal rotation of occiput anteriorly.
5. Crowning
After internal rotation of head descent occur, maximum diameter of head (biparietal diameter) stretches the vulval outlet.
6. Extension
Fetal head (sinciput, face and chin) sweep over perineum.
Delivery of fetal head by extension.
7. Restitution
Head externally rotates to face of right or left medial thigh of mother.
8. External rotation of head/ internal rotation of shoulder
Head rotates and anterior shoulder reaches pelvic floor and rotate anteriorly. Shoulder lie in anterio- posterio diameter of pelvic outlet.
9. Lateral flexion of body and shoulder through birth canal
After by hook method delivered the anterior shoulder and posterior and delivery of shoulder and trunk by lateral flexion.
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