Commonest cause of non - engagement at term, in primi is:

Engagement is said to occur when the greatest transverse diameter of the presenting part, has passed through the pelvic inlet. In all cephalic presentations, the greatest transverse diameter is always the biparietal. Engagement occurs in multipara with commencement of labour in the late Ist stage after rupture of membranes and in Nullipara during the last few weeks of pregnancy, i.e. ≈ 38 weeks In primi’s the most common cause of non engagement at term is deflexed head or occipitoposterior position followed by cephalopelvic disproportion (CPD). Since deflexed head or occipitoposterior is not given in option, we will go for CPD as the answer.