MECHANISM OF NORMAL LABOR IS THE FORMOST IMPORTANT TOPIC OF ALL CATORIES HEALTH CARE PERSONELL IN MIDWIFERY SUBJECT.

1. MECHANISM OF NORMAL
LABOR
BY
MADHUMITA SARKAR
SISTER TUTOR
NTS, ASANSOL
WEST BENGAL

2. DEFINITION
• 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.

3. TERMINALOGY
• LIE: the relation of long axis of the fetus to the long
axis of the centralized uterus or maternal spine
• ATTITUDE: the relation of the different parts of the
fetus to one another. So posture of the fetus is called
attitude.
 Head flexed over the chest
 Arms/hands flexed over the chest
 Thighs/ legs flexed over the abdomen
• PRESENTATION: the part of the fetus which occupies
the lower pole of the uterus. so the presenting part is
the portion of the body of the fetus

4. CONT…
• POSITION: The relation of the denominator
to the different quadrant of the pelvis/the
relation of an arbitrary chosen point of the
fetal presenting part to the right or left side
of the maternal birth canal
• DENOMINATOR: It is an arbitrary bony fixed
point on the presenting part which comes in
relation with the various quadrants of the
maternal pelvis

5. MECHANISM
• In normal labor, the head enters the brim
more commonly through the available
transverse diameter(70%) and to lesser extent
through one of oblique diameter.

6. CONT….
• The engaging transverse diameter is biparital 9.5cm.
• The principal movements are:
1. Engagement
2. Descent
3. Flexion
4. Internal rotation
5. Crowning
6. Extension
7. Restitution
8. External rotation and
9. Expulsion of the trunk

7. Cont….
• Engagement
Engagement takes place when the biparital
diameter of the fetal head has passed
through the pelvic inlet.
In primigravida, it is usually occurs within 12
hrs and multi gravid mother within 6 hours

8. CONT…
• DECENT
It is continuous movement throughout the
process of delivery. Descent result in number
of forces including contractions, and maternal
pushing effort with contraction of her
abdominal muscles.

9. Cont…
• FLEXION
• As the head descends, it means resistance
from the pelvic walls and floor and this leads
to increased flexion of the head.
• As the head flexed it brings shortest
longitudinal diameter of the head( sub
occipito bragmatic 9.5 cm) to pass through the
birth canal.

10. Cont…
• INTERNAL ROTATION OF THE HEAD
The occiput leads and meets the pelvic floor
first and rotates anteriorly 1/8 of circle

11. Cont…
• CROWNING
After internal rotation of head, further descent
occurs until the occiput lies underneath the
pelvic arch. At this stage, the maximum
diameter of head ( biparital diameter)
stretches the vulval outlet.

12. Cont……
• EXTENSION
Once crowning has occurred, the fetal head is
pivot under the symphysis pubis and the
sinciput, face and chin sweep over the
perineum

13. Cont….
• RESTITUTION
• With restitution, the occiput mover 1/8 of a
circle towards the side from which is started.

14. Cont……..
• INTERNAL ROTATION OF SHOULDER
The anterior shoulder reaches the pelvic floor
and rotates anteriorly 1/8th of circle. The
shoulder come to lie in the anterior posterior
diameter of pelvic outlet.

15. Cont………
• EXTERNAL ROTATION OF HEAD
• the head rotates 1/8th of the circle towards
the symphysis pubis from the oblique
diameter.

16. Cont…….
• LATERAL FLEXION OF BODY AND HEAD
• After the shoulder are delivered, the body is
born by lateral flexion

17. Thank you