Mechanism of labour All stages of labour

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 cross @ 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
1
1
A
B
i
i
F
c
D (A) vertex (B) sinciput (C) brow (D) face

5. 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
OP
LOT
ROT
LOA
ROA
LOP
ROP

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. 3
0
2
2.Engagement;descent, flexion 6. Restitution (external rotation)
3. Further descent, internal rotation
4. Complete rotation, beginning
extension
Cardinal movements in the
mechanism of labor and
delivery, left occiput
anterior position.

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

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