1. MECHANISM OF LABOUR Lateefa Al Dakhyel FRCSC, FACOG
Assistant professor & consultant
Obstetric & gynecology department
Collage of medicine
King Saud University

2. Lie, presentation, attitude, &position
FETAL LIE
The relation of the long axis of the fetus to that of the mother
1-Longitudinal lie -99% of labors at term
2-transverse lie  multiparty, placenta previa, hydramnious, & uterine anomalies
3-oblique lie -maternal & fetal axes 45 angle
-most unstable & become longitudinal Or transverse at labor.

3. ATTITUDE or posture.
In later months 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)
Change from this flexed attitude can cause abnormal presentations

4. .'" ' I
! 1\ 11 A B ii F c
(A) vertex
(B) sinciput
(C) brow D
(D) face

5. Vertex presentation  occiput Face presentation  mentum
Fetal position
The relation of a 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

7. 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 (incomplete breech) .

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

10. 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%

12. THE CARDINAL MOVEMENTS OF LABOUR
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

13. 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

14. 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.

15. 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

16. 5-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 (ant.fontanelle), forehead, nose, mouth & chin pass successively over the perineum

17. 6-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

18. 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

19. OCCIPUT POSTERIOR POSITION
Mechanism of labour is identical to OT & anterior varieties
Usually more longer.
The occiput rotate to the symphysis pubis through 135º instead of 90º or 45º
If rotation does not occur direct occiput post (5-10%)or
Partial rotation transverse arrest

20. ,. ,0
Mechanism of labor for right occiput posterior position, anterior rotation.

21. Q.1-Commonest presentation during labor is
1-left occiput anterior position (LOA)
2-right occiput anterior (ROA)
3-occiput transverse (OT)
4-left occiput posterior (LOP)
Q.2- about breach presentation which is correct
1-beech presentation is the more common in primeparous
2-incomlete breach can’t be delivered vaginally
3-breach presentation can’t be diagnosed clinically
4-all breach presentation should be delivered by C/S
Q.3-during labor
1-engagment occur when BPD reach the pelvic outlet
2-engagment always occur before onset of labor in prime.
3-if internal rotation to SP is 135 degree it will be OP
4-if the head is flexed it will be face presentation

22. Thank you