MECHANISM OF LABOUR (NORMAL & ABNORMAL)
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Transcript MECHANISM OF LABOUR (NORMAL & ABNORMAL)
MECHANISM OF LABOUR
(NORMAL & ABNORMAL)
DR. SALWA NEYAZI
CONSULTANT OBSTETRICIAN GYNECOLOGIST
PEDIATRIC & ADOLESCENT GYNECOLOGIST
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
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
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B
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(A) vertex
(B) sinciput
(C) brow
(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.
I
I
Longitudinal
presentation.
lie.
Frank
breech
Longitudinal lie. Complete breech
presentation.
Longitudinal lie. Incomplete, or footling,
breech presentation.
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
LONGITUDINAL LIE VERTEX PRESENTATION
LOA
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J
LOP
A. Right occiput posterior (ROP)
Right occiput transverse (ROT)
s
A
Longitudinal lie. Vertex presentation
S
f
a
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w
C
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p
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f
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Right occiput anterior (ROA).
FREQUENCY OF VARIOUS PRESENTATIONS &
POSITIONS AT TERM
Vertex 96%
2/3 Lt
1/3 Rt
Breech 3.5%
Face 0.3%
Shoulder 0.4%
Lt mento-ant
Rt mento-ant
Rt mento-post
Longitudinal lie. Face presentation. Left and right
anterior and ri posterior positions.
~
Longitudinal lie Breech presentation LSP
Transverse lie. Right acromiodorsoposterior position (RADP). The
shoulder of the fetus is to the mother's right, and the back is posterior.
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%
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
Anterior
asynclitism
Naegele's obliquity
Normal synclitism
Posterior asynclitism
Litzmann's obliquity Ear
presentation
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
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.
A
c
A
c
D
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.
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
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
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
Cardinal movements in the
mechanism of labor and
delivery,
left
occiput
anterior position.
3
0
2
2.Engagement;descent, flexion
6. Restitution (external rotation)
3. Further descent, internal rotation
4. Complete
extension
rotation,
beginning
3
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4
F
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v
b
a
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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).
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
,
.
,
0
Mechanism of labor for right
posterior position, anterior rotation.
occiput