Occipito- Posterior Position

OCCIPITO-POSTERIOR POSITION

INTRODUCTION

Occipitoposterior positions are the most common type of malposition of the occiput and occur in approximately 10% of labours. A persistent occipitoposterior position results from a failure of internal rotation prior to delivery. This occurs in 5% of deliveries. The vertex is presenting, but the occiput lies in the posterior rather than the anterior part of the pelvis. As a consequence, the fetal head is deflexed and larger diameters of the fetal skull is present.

DEFINITION

It is a vertex presentation where the occiput is placed posteriorly over the sacro-iliac joint or directly over the sacrum is called an occipito-posterior position.

INCIDENCE

-10% at onset of labour.

-Right occipito-posterior (ROP) is more common than left occipito-posterior (LOP) because:

·       The left oblique diameter is reduced by the presence of sigmoid colon.

·       The right oblique diameter is slightly longer than the left one.

·       Dextro-rotation of the uterus favours occipito-posterior in right occipito-anterior position.

ETIOLOGY

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- multiple pregnancy,

    d- polyhydramnios, e- pendulous abdomen

   

DIAGNOSIS

(A) During pregnancy:

• 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.
• Palpation:
• Fundal grip:
• The breech is felt as a soft, bulky, irregular non-ballotable mass.
• 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.
• 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.
• Second pelvic grip:
• The head is usually deflexed.
• 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.
• 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  RIGHT OCCIPITOPOSTERIOR POSITION (LONG ROTATION)

·       The lie is longitudinal.

·       The attitude of the head is deflexed.

·       The presentation is vertex.

·       The position is right occipitoposterior.

·       The denominator is the occiput.

·       The presenting part is the middle or anterior area of the left parietal bone.

·       The occiputofrontal diameter, 11.5cm, lies in the right oblique diameter of the pelvic brim. The occiput points to the right sacroiliac joint and the sinciput to the left iliopectineal eminence.

Flexion: Descent takes place with increasing flexion. The occiput becomes the leading part.

Internal rotation of the head: The occiput reaches the pelvic floor first and rotates forwards 3/8 of the circle along the right side of the pelvis to lie undre the symphosis pubis. The shoulders follow, turning 2/8 of a circle from the left to the right oblique diameter.

Crowning: The occiput escapes under the symphysis pubis and the head is crowned.

Extension: The sinciput, face and chion sweep the perineum and the head is born by a movement of extension.

Restitution: In restitution the occiput turns 1/8 of a circle to the right and the head realigns itself with the shoulders.

Internal rotation of the shoulders: The shoulders enter the pelvis in the right oblique diameter; the anterior shoulder reaches the pelvic floor first and rotates forwards 1/8 of a circle to lie under the symphysis pubis.

External rotation of the head: At the same time the occiput turns a futher 1/8 of a circle to the right.

Lateral flexion: The anterior shoulder escapes under the symphysis pubis, the posterior shoulder sweeps the perineum and the body is born by a moovement of lateral flexion.

(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%):

The head descends with some increase in flexion. The occiput reaches the pelvic floor and begins to rotate forwards. In mild deflexion, the occiput rotates 1/8 circle anteriorly and the head is arrested in the transverse diameter. Flexion is not maintained and the occipito-frontal diameter becomes caught at the narrow bispinous diameter of the outlet. Arrest may be due to weak contractions, a straight sacrum or a narrowed outlet.

(2) Short internal rotation -Persistent occipito-posterior (3%):

The term ‘persistent occipitoposterior position’ indicates that the occiput fails to rotate forwards. 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 pubis) (6%):

In marked deflexion, the sinciput meets the pelvic floor first, rotates 1/8 circle anteriorly and the occiput goes into the hallow of the sacrum. The baby is born facing the pubic bone.

*- 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.
4. 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.
• Contraindications of oxytocins:
• Disproportion.
• Incoordinate uterine action.
• Uterine scar e.g. previous C.S, hysterotomy, myomectomy, metroplasty or previous perforation.
• Grand multipara.
• Foetal distress.
• One of the following will occur:
• Long internal rotation 3/8 circle:
• occurs in about 90% of cases and delivery is completed as in normal labour.
• 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.
• Deep transverse arrest (1%) and persistent occipito-posterior (3%):
• The labour is obstructed and one of the following should be done:
• Vacuum extraction (ventouse):
• 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.
• Manual rotation and extraction by forceps:
• Under general anaesthesia the following steps are done:
• Disimpaction: the head is grasped bitemporally and pushed slightly upwards.
• Flexion of the head.
• 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.
• Fix the head abdominally by an assistant, apply forceps and extract it.
• Rotation and extraction by a forceps:
• Kielland’s forceps:
• Single application for rotation and extraction of the head as this forceps has a minimal pelvic curve.
• 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.
• 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.
• 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.
• Craniotomy:
• if the foetus is dead.

Actually speaking, the methods used in modern obstetrics are vacuum extraction and Caesarean section.

COMPLICATIONS

Apart from prolonged labour with its attendant risks to mother and fetus and the increased likelihood of instrumental delivery, the following complications may occur.

(1)  Obstructed labour

This may occur when the head is deflexed or partially extended and becomes impacted in the pelvis.

(2)  Maternal trauma

Forceps delivery may results in perineal bruising and trauma. Delivery of the fetus in the persistent occipitoposterior position, particularly if previously undiagnosed, may cause a third degree tear.

(3)  Neonatal trauma

Neonatal trauma occurring following delivery from an occipitoposterior position has been associated with forceps or ventose delivery. The outcome for a neonate delivered from an occipitoposterior position is comparable to that expected for an infant delivered from an occipitoanterior position.

(4)  Cord prolapsed

A high head predisposes to early spontaneous rupture of the membranes, which together with an ill-fitting presenting part, may result in cord prolapsed.

(5)  Cerebral haemorrahage

The unfavourable upward moulding of the fetal skull, found in an occipitoposterior position, can cause intracranial haemorrhage, as aresult of the falx cerebri being pulled away from the tentorium cerebella. The larger presenting diameters also predispose to a greater degree of compression. Cerebral haemorrhage may also result from chronic hypoxia, which may accompany prolonged labour.

CONCLUSION

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

BIBLIOGRAPHY

Books

1.     Annamma Jacob, “A COMPREHENSIVE TEXT BOOK OF MIDWIFERY”, 1^st edition, Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, 2005, Page No: 422-431.

2.     Dutta D.C., “TEXT BOOK OF OBSTETRICS”, 4^th edition, New central book agency, Calcutta, 1998, Page No: 365-374.

3.     Norman F. Gant, “WILLIAMS OBSTETRICS”, 21st edition, Library of Congress Cataloging in Publication, 2001, Page No. 335-342.

4.     Diane M. Fraser, “MYLES TEXTBOOK FOR MIDWIVES”, 14^th edition, Library of Congress Cataloging in Publication,2003,Page No. 551-564.

Website

5.     http://www.gfmer.ch/Obstetrics_simplified/malpresentations_and_malposition.html

6.     http://www.google.co.in/imgres?imgurl=http://www.arabicobgyn.net/doc/

7.     http://www.gpnotebook.co.uk/simplepage.cfm?ID