Occiput-Posterior Position (OP)
INTRODUCTION:
- An abnormal position of the vertex rather than an abnormal presentation.
- In a vertex presentation when occiput is placed posteriorly over the sacro -illiac joint or directly over sacrum, it is called occipito -posterior position
- When the occiput is placed over right sacro-illiac joint , Right occipito-posterior(ROP)/3 RD position of vertex.
- When the occiput is placed over left sacroilliac joint, Left occipito -posterior(LOP)also called 4 th position of vertex.
- when it points towards sacrum, is called Direct occipito-posterior
CAUSES :
MATERNAL
- Shape of inlet- Anthropoid/android pelvis more than 50% cases because the wide occiput can be comfortably placed in wider posterior segment of pelvis
FETAL
- Marked deflection of head favours posterior position. It occurs due to
- High pelvic inclination.
- placenta previa
- pelvic tumours
- Primary brachycephaly
- UTERINE –Abnormal uterine contraction
DIAGNOSIS:
Inspection:
- Abdomen looks flat below the umbilicus.
Palpation:
- Fundal height :- corresponds with period of amenorrhoea.
- Fundal grip :- breech.
- Lateral grip :-Foetal back is felt on rt. Flank of mother in ROP & in left flank, in LOP.
- Fetal limbs are felt easily as knob like structure anteriorly.
- Pelvic grip :-Head is not engaged.
- Cephalic prominance (sinciput) is not felt so prominent as found in well flexed occipito –anterior.
- In direct occipito – posterior the small sinciput is confused with breech.
- Auscultation : FHS is best heard in flank in direct occipito – posterior / R.O.P. -but difficult in L.O.P.
Vaginal examination :-
- Finding depends upon degree of flexion of head.
- Confirmation made during 2nd stage of labour:-
- Sagittal suture:- occupies any of the oblique diameter of pelvis.
- Posterior fontanelle :-felt near the sacro-iliac joint.
- Anterior fontanelle :- felt near the ilio-pectineal eminence.
- The diagnosis by vaginal examination may be difficult due to the formation of caput succedaneum over the presenting part.
MECHANISM OF LABOUR:
FAVOURABLE CASES(90%):
- Good uterine contraction results in good flexion of head.
- Normal descent occur up to pelvic floor.
- Occiput rotates 3/8th of a circle(135degree) anteriorly to lie behind symphysis pubis.
- Shoulders rotate about 2/8th of circle to occupy oblique diameter.
- Rest of the mechanism is like that of right occipitoanterior in ROP & left occipitotanterior in LOP.
- In persistent occipitoposterior position, spontaneous delivery occurs as face to pubis.
- Delivery of brow, vertex, occiput lastly face is born by extension .
- Restitution ,external rotation &delivery of trunk occurs normally
UNFAVOURABLE CASES(10%):
- Non rotation or malrotation
- Certain cases occiput fails to rotate-
- Deflexion of the head
- Weak uterine contraction
- Flat sacrum
- Prominent ischial spine
- Convergent side walls
- Weak pelvic floor muscles
- Big baby
- Early drainage of liquor
TYPES:
Incomplete forward rotation
- Occiput rotates 1/8 th of circle sagital suture comes to lie in bispinous diameter results in Deep transverse arrest.
- It occurs in mild deflexion of head.
Nonrotation :
- Both sinciput & occiput reaches pelvic floor at same time & sagital suture lies in oblique diameter results in Oblique posterior arrest.
- It occurs inmoderate deflexion of head.
Malrotation :
- Sinciput touches pelvic floor first resulting in anterior rotation of sinciput 1/8th of circle putting occiput to sacral hollow called Persistent Occiput-posterior Position of vertex.
- It occurs in extreme deflexion. Also called occipito -sacral position.
Exam Important
- Persistent occipitoposterior is common in the Anthropoid type of pelvis
- The commonest cause of occipitoposterior position of fetal head during labor is android pelvis
- Most unfavourable presentation for vaginal delivery is / delivery not possible per vaginum is Mento posterior
Don’t Forget to Solve all the previous Year Question asked on Occiput-Posterior Position (OP)
Click Here to Start Quiz
Click Here to Start Quiz
