1. MECHANISM OF LABOUR (NORMAL & ABNORMAL)
Presented By
Dr. ZEINAB ABOTALIB MRCOG, DGO,
Associate Professor &
Consultant Obs/Gyna Infertility & IVF

2. Lie, presentation, attitude, &position
FETAL LIE
The relation of the long axis of the fetus to that of the mother
Longitudinal lie is found in 99% of labours at term
Predisposing factors for transverse lie/oblique lie  multiparity, placenta previa, hydramnious, & uterine anomalies
FETAL PRESENTATION
The presenting part is the portion of the body of the fetus that is foremost in the birth canal
The presenting part can be felt through the Cx on vaginal examination
Longitudinal lie  cephalic presentation
breech presentation
Transvrse lie  shoulder presentation

3. Lie, presentation, attitude, &position
CEPHALIC PRESENTATION
Head is flexed sharply  vertex / occiput presentation
Head is extended sharply  face presentation
Partially flexed  bregma presenting (sinciput presentation)
Partially extended  brow presentation
BREECH PRESENTATION
Frank breech
Complete breech
Footling breech
ATTITUDE
Posture of the fetus folded on itself to accommodate the shape of the uterus
Flexed head, thighs, knees &feet
The arms crossed over the chest
Face presentation extended concave contour of the vertebral column

4. (A) vertex (B) sinciput (C) brow (D) face c I D A B
.'" ' I
! 1\ 11 A B ii F c
(A) vertex
(B) sinciput
(C) brow D
(D) face
Longitudinal lie. Ce­phalic presentation. Differences in attitude of fetal body,
Note changes in fetal attitude in relation to fetal vertex as the fetal head becomes less flexed.

5. Longitudinal lie. Frank breech presentation.
I I
Longitudinal lie. Frank breech presentation.
Longitudinal lie. Complete breech presentation.

6. Longitudinal lie. Incomplete, or footling, breech presentation.

7. POSITION
The relation of an arbitrary chosen point of the fetal presenting part to the Rt or Lt side of the maternal birth canal
The chosen point
Vertex presentation  occiput
Face presentation  mentum
Breech presentation Sacrum
Each presentation has two positions Rt or Lt
Each position has 3 varieties : Ant, transverse, post OA
ROA
LOA
ROT
LOT
ROP
LOP OP

8. LONGITUDINAL LIE VERTEX PRESENTATION
LOP
LOA ~
'tJ

9. A. Right occiput posterior (ROP) Right occiput transverse (ROT)
Longitudinal lie. Vertex presentation

10. c Right occiput anterior (ROA). Sf a! w Cc ht p( fit tb fe w
al ta tb oj

11. FREQUENCY OF VARIOUS PRESENTATIONS & POSITIONS AT TERM
Vertex  96%
2/3 Lt
1/3 Rt
Breech  3.5%
Face 0.3%
Shoulder 0.4%

12. Lt mento-ant Rt mento-ant Rt mento-post
Longitudinal lie. Face presentation. Left and right anterior and posterior positions.

13. Longitudinal lie Breech presentation LSP~
Longitudinal lie Breech presentation LSP

14. Transverse lie. Right acromiodorsoposterior position (RADP)
Transverse lie. Right acromiodorsoposterior position (RADP). The shoulder of the fetus is to the mother's right, and the back is posterior.

15. MECHANISM OF LABOUR WITH OCCIPUT PRESENTATIONS THE CARDINAL MOVEMENTS OF LABOUR
1-ENGAGEMENT
The greatest transverse diameter BPD passes through the pelvic inlet
It may occur in the last few weeks of pregnancy or only in labour especially in multipara
The fetus enters the pelvis in transverse or oblique diameter
LOT  40%
ROT 20%
OP 20% ROP >LOP
ROA / LOA 20%

16. THE CARDINAL MOVEMENTS OF LABOUR
Asynclitism
The sagittal sutures of the head deflects ant towards the symphysis pubis or post towards the sacrum
2-DESCENT
In nullipara engagement takes place before the onset of labour & further descent may not occur till the 2nd stage
In multipara descent begins with engagement
It is gradually progressive till the fetus is delivered
It is affected by the uterine contractions & thinning of the lower segment

17. Anterior asynclitism Naegele's obliquity
Normal synclitism
Posterior asynclitism Litzmann's obliquity Ear presentation

18. 3-FLEXION
The descending head meets resistance of pelvic floor, Cx & walls of the pelvis   flexion
The shorter suboccipito-begmatic is substituted for the longer occipito-frontal

19. Lever action producing ftexion of the head; conversion from occipitofrontal to suboccipitobregmatic diameter typically reduces the anteroposterior diameter from nearly 12- to 9.5 cm.

20. A. Flexion poor. B. Flexion moderate. C. Flexion advanced.
Four degrees of head flexion. Indicated by the solid line the occipitomental diameter; the broken line connects the center of the anterior fontanel with posterior fontanel:
A. Flexion poor.
B. Flexion moderate.
C. Flexion advanced.
D. Flexion complete.
Note that with flexion com­plete the chin is on the chest, and the suboccipitobregmatic diameter, the shortest anteroposterior diameter of the fetal head, is passing through the pelvic inlet. A c A c D

21. 4-INTERNAL ROTATION
Turning of the head from the OT position  anteriorly towards the symphysis pubis ie. Occiput moves from transverse to ant 45º
Less commonly OT  posteriorly towards the sacrum 135º
It is not accomplished till the head has reached the spines
The levator ani muscles form a V shaped sling that tend to rotate the vertex anteriorly
It is completed by the time the head reaches the pelvic floor 2/3 or shortly after ¼

22. EXTENSION
When the flexed head reaches the vulva it undergoes extension  the base of the occiput will be in direct contact with the inferior margin of the symphysis pubis
Crowning  the largest diameter of the fetal head is encircled by the vulvar ring
The head is born by further extension as the occiput, bregma, forehead, nose, mouth & chin pass successively over the perineum

23. EXTERNAL ROTATION RESTITUTION
After delivery of the head it returns to the position it occupied at engagement , the natural position relative to the shoulders (oblique position)Restitution
Then the fetal body will rotate to bring one shoulder anterior behind the symphysis pubis ( biacromial diameter into the APD of the pelvic outlet)
Restitution is followed by complete external rotation to transverse position (occiput lies to next to Lt maternal thigh)
The ant shoulder slips under the pubis
By lateral flexion of the fetal body the post shoulder will be delivered & the rest of the body will follow

24. 2.Engagement;descent, flexion 6. Restitution (external rotation)
Cardinal movements in the mechanism of labor and delivery, left occiput anterior position.
302
2.Engagement;descent, flexion
6. Restitution (external rotation)
3. Further descent, internal rotation
4. Complete rotation, beginning extension

25. 304
F tl v b
a f s
Mechanism of labor for the left occiput transverse position, lateral view. Posterior asynclitism (A) at the pelvic brim followed by lateral flexion, resulting in anterior asynclitism (B) after engagement, further descent (C), rotation, and exten­sion (D).

26. OCCIPUT POSTERIOR POSITION
Mechanism of labour is identical to OT & anterior varieties
The occiput rotate to the symphysis pubis through 135º instead of 90º or 45º
If rotation does not occur direct occiput post or
Partial rotation transverse arrest

27. ,. ,0
Mechanism of labor for right occiput posterior position, anterior rotation.