Occiput-Posterior Position (OP)

In more than 50% of cases, the occipito-posterior position is associated with either an anthropoid or android pelvis.

Persistent occipitoposterior is an abnormal mechanism of the occipito-posterior position where there is malrotation of the occiput posteriorly towards the sacral hollow (occipito-sacral position). Delivery may occur spontaneously as face-to-pubis but arrest may occur in this position and is called occipito-sacral arrest.

Ans. is d i.e. Android pelvis

Ocipito-posterior position 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 normal course like that of an occipito-anterior position. In certain types of pelvis like android and anthropoid, it is a favourable position.

Causes of occipito-posterior position

• Shape of pelvic inlet : in more than 50% cases the occipito-posterior position is associated with either an android or an anthropoid pelvis. The wide occiput can comfortably be placed in the wider posterior segment of the pelvis.
• Fetal factors : marked deflexion of the fetal head too often favours posterior position of vertex. Causes of deflexion of head : a. High pelvic inclination

1. Attachment of the placenta on the anterior wall of uterus.
2. Primary brachy-cephaly

• Uterine factors : Abnormal uterine contraction which may be the cause or effect, leads to persistent deflexion and occipito-posterior position.