OCCIPITO-POSTERIOR
POSITION
1-Definition
2-Aetiology
3-Diagnosis a-during
pregnancy
b-during labour
4-Mechanism of labour:a-normal
mechanism 90%
b-abnormal
mechanism 10%
1-Deep transverse arrest 1%
2-Persistent
O.P 3%
3-Dirct
O.P(face-pubis)6%
5-Management.
a-first stage
b-2nd
stage..1-face-pubis(generous episiotomy)
2-deep transverse arrest
3-persistent O.P..in 2,3 obstructed labour:
a-vacum b-manual
rotation and forceps extraction
c-rotation and
extraction by forceps: kielland,Barton
Scanzoni duble
application
d-CS
e-craniotomy
6-complication of O.
Definition
It is a vertex
presentation with foetal back directed posteriorly.
Incidence:
10% at onset of
labour.
Right occipito-posterior
(ROP) is more common than left occipito-posterior (LOP)
because:
1. The left
oblique diameter is reduced by the presence of sigmoid
colon.
2. The
right oblique diameter is slightly longer than the left
one.
3. Dextro-rotation
of the uterus favours occipito-posterior in right
occipito-anterior position.
Aetiology:
1. The
shape of the pelvis: anthropoid and android pelvis are
the most common cause of occipito-posterior due to
narrow fore-pelvis.
2. Maternal
kyphosis: The convexity of the foetal back fits with the
concavity of the lumbar kyphosis.
3. Anterior
insertion of the placenta: the foetus usually faces the
placenta (doubtful).
4. Other
causes of malpresentations: as a placenta praevia,
b- pelvic tumours,
c pendulous abdomen,
d-polyhydramnios,
e multiple pregnancy.
Diagnosis:
(A) During pregnancy:
(I) Inspection:
The abdomen looks
flattened below the umbilicus due to absence of round
contour of the foetal back.
A groove may be
seen below the umbilicus corresponding to the neck.
Foetal movement may
be detected near the middle line.
(II) Palpation:
1-Fundal grip:
The breech is felt
as a soft, bulky, irregular non-ballotable mass.
2-Umbilical grip:
- The back felt
with difficulty in the flank away from the middle line.
- The anterior
shoulder is at least 3 inches from the middle line.
- The limbs are
easily felt near, or on both sides, of the middle line.
3-First pelvic
grip:
- The head is
usually not engaged due to deflexion.
- The head is felt
smaller and escapes easily from the palpating fingers as
they catch the bitemporal diameter instead of the
biparietal diameter in occipito-anterior.
4-Second pelvic
grip:
The head is usually
deflexed.
(III) Auscultation:
- FHS are heard in
the flank away from the middle line.
- In major degree
of deflexion, the FHS may be heard in middle line.
(IV) Ultrasonography or
lateral view x-ray.
(B) During labour:
In addition to the
previous findings vaginal examination reveals:
The direction of
the occiput.
The degree of
deflexion.
Mechanism of Labour:
*A certain degree
of deflexion is present due to :
a-Opposition of the
two convexities of the foetal and maternal spines
prevents flexion and promotes deflexion.
b-The longer
biparietal diameter (9.5cm) enters the narrow
sacro-cotyloid diameter (9cm) while the shorter
bitemporal diameter (8cm) enters the longer oblique
diameter (12cm).
**As a result of
deflexion, the occipito-frontal diameter 11.5 cm enters
the pelvis leading to delayed engagement.
**Taking in
consideration the rule that the part of the foetus that
meets the pelvic floor first will rotate anteriorly, the
degree of deflexion determines the mechanism of labour
as follow:
(A) Normal
mechanism(90%):
Deflexion is
corrected and complete flexion occurs. The occiput meets
the pelvic floor first, long anterior rotation 3/8
circle occurs bringing the occiput anteriorly and the
foetus is delivered normally.
Factors favouring long
anterior rotation:
(1) Well flexed
head.
(2) Good uterine
contractions.
(3) Roomy pelvis.
(4) Good pelvic
floor.
(5) No premature
rupture of membranes.
Causes of failure of
long anterior rotation:
(1) Deflexed head.
(2) Uterine
inertia.
(3) Contracted
pelvis: rotation of the head cannot easily occur in
android pelvis due to projection of the ischial spines
and convergence of the side walls.
(4) Lax or rigid
pelvic floor.
(5) Premature
rupture of membranes or its rupture early in labour.
(B) Abnormal mechanism
(10%):
(1) Deep transverse
arrest (1%):
In mild deflexion,
the occiput rotates 1/8 circle anteriorly and the head
is arrested in the transverse diameter.
(2) Persistent occipito-posterior
(3%):
In moderate
deflexion, the occiput and sinciput meet the pelvic
floor simultaneously, no internal rotation and the head
persists in the oblique diameter.
(3) Direct occipito-posterior
(face to bubis) (6%):
In marked deflexion,
the sinciput meets the pelvic floor first, rotates 1/8
circle anteriorly and the occiput becomes direct
posterior.
*- In deep
transverse arrest and persistent occipito-posterior no
further progress occurs and labour is obstructed as the
head cannot be delivered spontaneously.
*- In direct
occipito-posterior, the head can be delivered by flexion
supposing that the uterine contractions are strong and
there is no contracted pelvis.However, perineal
lacerations are more liable to occur as :
the vulva is
distended by the large occipito-frontal diameter 11.5
cm,
the perineum is
overstretched by the large occiput.
Management of Labour:
A- First stage:
1-Exclude
contracted pelvis.
2-Exclude
presentation or prolapse of the cord.
3-Inertia and
prolonged labour are expected so oxytocin may be
indicated unless there is contraindication.
-Contractions are
sustained, irregular and accompanied by marked backache
which needs analgesia as pethidine or epidural
analgesia.
5-Avoid premature
rupture of membranes by:-
* rest in bed,
*no straining,
*avoid high enema,
*minimise vaginal
examinations.
6- The other
management and observations as in normal labour.
B- Second stage:
Wait for 60-90
minutes.
During this period:
- Observe the
mother and foetus carefully.
- Combat inertia by
oxytocin unless it is contraindicated.
N.BContraindications
of oxytocins:
1-Disproportion.
2-Incoordinate
uterine action.
3-Uterine scar e.g.
previous C.S, hysterotomy, myomectomy, metroplasty
4-previous
perforation.
5-Grand multipara.
6-Foetal distress.
One of the following
will occur:
(I) Long internal
rotation 3/8 circle:
occurs in about 90%
of cases and delivery is completed as in normal labour.
(II) Direct
occipito - posterior (face to pubis):
- occurs in about
6% of cases.
- the head can be
delivered spontaneously or by aid of outlet forceps.
- Episiotomy is
done to avoid perineal laceration.
(III) Deep
transverse arrest (1%) and persistent occipito-posterior
(3%):
The labour is
obstructed and one of the following should be done:
(A) Vacuum extraction (ventose):
- Proper
application as near as possible to the occiput will
promote flexion of the head.
- Traction will
guide the head into the pelvis till it meets the pelvic
floor where it will rotate.
(B) Manual rotation and
extraction by forceps:
Under general
anaesthesia the following steps are done:
1-Disimpaction: the
head is grasped bitemporally and pushed slightly
upwards.
2-Flexion of the
head.
3-Rotation of the
occiput anteriorly by the right hand vaginally aided by,
- Rotation of the
anterior shoulder abdominally towards the middle line by
the left hand or an assistant.
4-- Fix the head
abdominally by an assistant, apply forceps and extract
it.
(C) Rotation and
extraction by a forceps:
1- Kielland’s
forceps:
Single application
for rotation and extraction of the head as this forceps
has a minimal pelvic curve.
2- Barton’s
forceps:
- Originally was
designed for deep transverse arrest.
- It has a hinge in
one blade between the blade proper and shank to
facilitate application.
- The axis of the
handle to that of the blades is 55o i.e. the angle of
the pelvic inlet to the outlet.
- It is used for
rotation only then conventional forceps is applied for
extraction unless it has an axis traction piece so it
can be used for rotation and extraction.
3- Scanzoni
double application:
- The conventional
forceps is applied to rotate the occiput anteriorly then
the forceps is removed and reapplied so that the pelvic
curve of the forceps is directed anteriorly and extract
the head.
- This method is
out of modern obstetrics as it is hazardous to the
mother and foetus.
N.B. The head
should be engaged for manual or forceps rotation to be
done.
(D) Caesarean
section:
It is indicated in
:
Failure of the
above methods.
Other indications
for C.S as;
contracted
pelvis,
placenta praevia,
prolapsed
pulsating cord before full cervical dilatation, and
elderly
primigravida.
(E) Craniotomy:
if the foetus is
dead.
Actually speaking,
the methods used in modern obstetrics are:
- Vaccum extraction
and
- Caesarean
section.
Complications:
See complications
of malpresentations and malposition (mentioned before).
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