benefited to UG and PG nursing aspirants

1. OCCIPITO-POSTERIOR POSITION
JASMI MANU
HEAD OF THE DEPARTMENT
OBS/GYN DEPARTMENT
RCN

2. DEFINITION
 In a vertex presentation where the occiput is placed
posteriorly over the sacro-iliac joint or directly over
the sacrum, it is called an occipito-posterior
position.
 When the occiput is placed over the right sacro-iliac
joint, the position is called right occipito-posterior
and when placed over the left sacro-iliac joint, is
called left occipito-posterior (L.O.P)
 and when it points towards the sacrum, is called
direct occipito-posterior.
 All the three positions may be primary (present
before the onset of labour) or secondary
(developing after labour starts).

4.  Occipito-posterior is an abnormal position of the
vertex rather than an abnormal presentation. In
the majority of cases (90%), anterior rotation of the
occiput occurs and follows the course like that of an
occipitoanterior and moreover, in certain type of
pelvis (anthropoid), it is a favorable position. But as
the posterior position occasionally gives rise to
dystocia, it is described along with
malpresentation.

5. INCIDENCE
 At the onset of labour, the incidence is about 10%
of all the vertex presentations.
 The incidence is expected to be more during late
pregnancy and is much less in late second stage of
labour.
 Right occipito-posterior is 5 times more common
than the left Foccipito-posterior.
 Dextro-rotation of the uterus and the presence of
the sigmoid colon on the left, disfavour L.O.P.
position.

6. CAUSE
 In the majority, the cause of the abnormal position
is not clear.
The following are the responsible factors:
 Shape of the pelvic inlet In more than 50%
occipito-posterior position is associated with either
an anthropoid or android pelvis.
 The wide occiput can comfortably be placed in the
wider posterior segment of the pelvis.

7.  Fetal factors: Marked deflection of the fetal head,
too often favours posterior position of the vertex.
The causes of deflexion are :
 High pelvic inclination.
 Attachment of the placenta on the anterior wall of the
uterus — This favours the well flexed fetal ovoid
looking towards the anterior wall of the uterus i.e.
remains in dorso-posterior position. Thus, the
convexities of the fetal and maternal spines are
apposed, leading to tendency of extension of the fetal
spines with persistent deflexed attitude of the head.
 Uterine factor: Abnormal uterine contraction
which may be the cause or effect, leads to
persistent deflexion and occipito-posterior
position.

8. DIAGNOSIS
 Abdominal examination
 Inspection : The abdomen looks flat, below the
umbilicus.
 Umbilical grip : The findings are :
 The fetal limbs are more easily felt near the midline on either
side.
 The fetal back is felt far away from the midline on the flank and
often difficult to outline clearly.
 The anterior shoulder lies far away from the midline.
 Pelvic grips : The findings are :
 The head is not engaged.
 The cephalic prominence (sinciput) is not felt so prominent as
found in well flexed occipito-anterior. In direct occipito-
posterior, the small sinciput is confused with breech.

9.  Auscultation : The maximum intensity of the fetal
heart sounds is heard on the flank and often
difficult to locate specially in L.O.P. However, in
direct occipito-posterior, the F.H.S. is distinctly felt
in the midline.
Abdominal contour in (a) posterior (b) anterior positions of
vertex presentation

10. VAGINAL EXAMINATION
 The findings in early labour are :
 Elongated bag of membranes which is likely to rupture during
examination.
 The sagittal suture occupies any of the oblique diameters of
the pelvis.
 Posterior fontanelle is felt near the sacro-iliac joint.
 The anterior fontanelle is felt more easily because of deflexion
of the head and at times, is felt at a lower level than the
posterior one
 In late labour, the diagnosis is often difficult because of
caput formation which obliterates the sutures and
fontanelles. In such cases, the ear is to be located and
the unfolded pinna points towards the occiput. Simul-
taneous assessment of the pelvis should be done.

11. IMAGING
 Ultrasonography is rarely done. It is helpful to know
the descent, attitude of the head and its relation to
the pelvic walls (position).

15. MECHANISM OF "FACE TO PUBIS" DELIVERY
 Further descent occurs until the root of the nose
hinges under the symphysis pubis.
 Flexion occurs — releasing successively the brow,
vertex and occiput out of the stretched perineum and
then the face is born by extension.
 Restitution : The head moves 1 / 8th of a circle in the
opposite direction of internal rotation thus turning the
face to look towards the mother's left thigh in R.O.P. and
right thigh in L.O.P.-
 External rotation : The occiput further rotates to the
same direction of restitution to l/8th of a circle placing
finally the face looking directly towards the left thigh in
R.O.P. and the right thigh in L.O.P.