Mechanism of Labour in Face Presentation

Here in this article, we will discuss one of the rare varieties of cephalic presentation is the face. It is more common in multiparae.

Lie – Longitudinal
Presentation – Cephalic
Presenting part – Face
Attitude – Complete flexion of the limbs or complete extension of the head
Denominator – Mentum
Position – 4 Positions of the face in relation to the left and right sacroiliac joints or the right and left iliopectineal eminences.

1st Face- Right mento-posterior (RMP)
2nd Face- Left mento-posterior (LMP)
3rd Face- Left mento-anterior (LMA), Commonest position
4th Face- Right mento-anterior (RMA)

Some of the reasons are-

-Multi parity with a pendulous abdomen
-Contracted pelvis / Flat pelvis
–Pelvic tumors
-Congenital malformations
-Twist of the cord around the neck

MECHANISM OF LABOUR ( Mento-anterior, LMA / RMA) –

1. Engagement – The engaging diameter is the right oblique in LMA, left in RMA, and the mentum lies at the iliopectineal eminence and the glabella to the opposite sacroiliac joint. The engaging diameter of the head is submento-bregmatic 9.5 cm in a fully extended head and the engagement becomes delayed.

2. Descent and extension – With the increasing extension, the chin touch the pelvic floor.

3. Internal rotation of chin – It occurs through 1/8th of a circle anteriorly, and the mentum comes behind the symphysis pubis and this continues until the submentum hinges under the pubic arch.

4. Delivery of the head – Now the head is born by flexion, the chin, face, brow, vertex, and the occiput is released. Submento- vertical 11.5 cm distend the vulval outlet.

5. Restitution – It occurs through 1/8th of a circle opposite to the direction of internal rotation.

6. External rotation – Occurs 1/8th of a circle to the same side of restitution so the face looks toward the left thigh in LMA and right thigh in RMA.

7. Lateral flexion – The anterior shoulder followed by the posterior shoulder and then the trunk is released by lateral flexion.

Mento-posterior position (20-25%) (RMP / LMP) –

-Anterior rotation of the mentum occurs in only 20% of cases.

– In 80%, incomplete anterior rotation, non-rotation or short posterior rotation of the mentum occurs. ( All in these positions arrest occurs with average size pelvis and fetal head and no spontaneous delivery in persistent mento-posterior position.)

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