This is where the head is extended such that the face presents. The presenting diameter is submento-bregmatic, averaging 9.5 cm.
It occurs in 1 in 500 deliveries, and is less favourable than OP (occipitoposterior). Progress depends on the relative sizes of foetus and pelvis.
Mento-anterior is the more favourable presentation.
The delivery may convert to OA in much the same way as OP, this can be assisted by manually flexing the head. Turning the head to mento-anterior has advantages.
Last reviewed 01/2018