mechanism of labour

1. MECHANISM OF LABOUR/ CARDINAL
MOVEMENT
Prepared By:
Sabita Khadka
Midwifery Officer
KAHS, Jumla

4. Fetal skull and diameter

6. MECHANISM OF LABOUR/ CARDINAL
MOVEMENT
• The series of movements that occur on the
head in the process of adaptation during its
journey through the pelvis is called
mechanism of labor.
• Is a series of passive movements of the fetus
in the passage through the birth canal.

7. Contd…
• The ability of the fetus to successfully
negotiate the pelvis during labor involves
changes in position of its head during its
passage in labor. The mechanisms of labor,
also known as the cardinal movements, are
described in relation to a vertex presentation,
as is the case in 95% of all pregnancies.

10. Criteria for normal mechanism of
labour
• Lie: Longitudinal
• Presentation: Cephalic
• Position: right or left occipitoanterior
• Attitude: well flexion
• Denominator: occiput
• Presentiong part: posterior part of the
anterior parietal bone

11. Steps of Mechanism of Labour
• Engagement
• Descent
• Flexion
• Internal rotation of the head
• Crowning
• Extension of the head
• Restitution
• Internal rotation of the shoulder
• External rotation of the head
• Lateral flexion of the body

13. 1. Engagement
• The widest diameter of the presenting part
(with a well-flexed head, where the largest
transverse diameter of the fetal occiput is the
biparietal diameter) enters the maternal pelvis
to a level below the plane of the pelvic inlet.
On the pelvic examination, the presenting part
is at 0 station, or at the level of the maternal
ischial spines.

17. 2. Descent
• Descent of the fetal head into the pelvis often
begins before the onset of labour. For a
primigravid women this usually occurs during
the latter weeks of pregnancy. In multigravid
women muscle tone is often more lax and
therefore descent and engagement of the
fetal head may not occur until labour actually
begins.

18. Contd…
• The downward passage of the presenting part
through the pelvis. This occurs intermittently
with contractions. The rate is greatest during
the second stage of labor.

19. Descent

20. Contd…
• Throughout the first stage of labour the
contraction and retraction of the uterine
muscles reduces the capacity in the uterus,
exerting pressure on the fetus to descend
further. Following rupture of the forewaters
and the exertion of maternal effort,progress
speeds up.

23. 3. Flexion
• As the fetal vertex descents, it encounters
resistance from the bony pelvis or the soft
tissues of the pelvic floor, resulting in passive
flexion of the fetal occiput. The chin is brought
into contact with the fetal thorax, and the
presenting diameter changes from
occipitofrontal (11.0 cm) to
suboccipitobregmatic (9.5 cm) for optimal
passage through the pelvis.

24. 3. Flexion

25. 4. Internal rotation of the head
• As the head descends, the presenting part,
usually in the transverse position, is rotated
about 45° to anteroposterior (AP) position under
the symphysis.
• In a well flexed vertex presentation the occiput
leads and rotate anteriorly through 1/8th of the
circle when it meets the pelvic floor.
• Internal rotation brings the AP diameter of the
head in line with the AP diameter of the pelvic
outlet.

26. Crowning
• The occiput slips beneath the subpubic arch
and crowning occurs when the head no longer
return back between the contractions and the
widest transverse diameter (biparietal) is
born.

27. 5. Extension
• With further descent and full flexion of the
head, the base of the occiput comes in contact
with the inferior margin of the pubic
symphysis. Upward resistance from the pelvic
floor and the downward forces from the
uterine contractions cause the occiput to
extend and rotate around the symphysis. This
is followed by the delivery of the fetus' head.

28. 7. Restitution
• When the fetus' head is free of resistance, it
untwists about 45° left or right, returning to
its original anatomic position in relation to the
body.

29. 8. Internal rotation of the shoulder
• The shoulder undergo a similar rotations to
that of the head to lie in the widest diameter
of the pelvic outlet, namely Anterioposterior.
• The anterior shoulder is the first to reach the
levator ani muscles and it therefore rotates
anteriorly to lie under the symphasis pubis.

30. Contd…
• This movement can be clearly seen as the
head turns at the same time, external rotation
of the head.
• Its occurs at the same direction as restitution.
And the occiput of the fetal head now lies
lateral.

31. 9. Lateral flexion
• The shoulder are usually born sequentially.
The anterior shoulder born first and the
posterior shoulder.
• Then body will be delivered.

36. • Dutta DC, 2011, Textbook of Obstetrics; 7th
edition; New Central Book Agency(P) Ltd; India;.
• Myles; 2015,Textbook for Midwives;5th edition;
Churchil Livingstone; Elsevier;
• Subedi D., Gautam S.;Midwifery Nursing Part 2,
1st edition, Medhavi Publication, Kathmandu.
• Jacob A.; Comprehensive Textbook of Midwifery
and Gynecological Nursing; 3rd edition; Ansari
Road, India; Jaypee Brothers Medical
Pubishers(P) Ltd.
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