Page 239 - Critical Maternity & Newborn Health Nursing

D) Vaginal examination during labor:

When the cervix is sufficiently dilated especially after rupture of

membranes, the bony landmarks are felt: the orbital margin, nose,

mouth, and the chin.

Mechanism of Labor:

1- Mento-Anterior:

The head descends with the submento-bregmatic diameter (9.5 cm).

There is descent, increased extension of the head so the chin meet

the pelvic floor first and rotates forward 1/8 of a circle. With further

descent the submental region appears below the symphysis pubis

and the head is delivered by flexion. This is followed by restitution

and external rotation of chin as in vertex presentation.

2- Mento-posterior

a- In 2/3 of cases the chin rotates forwards 3/8 of a circle and is

delivered as mento anterior.

b- In 1/3 of cases the chin rotates forwards 1/8 of a circle and this

is known as deep transverse arrest of the face.

Or it does not rotate at all and remains as persistent mento-posterior,

or the chin backward 1/8 of a circle towards the concavity of the
sacrum, this is direct mento-posterior. In all these cases labor

becomes obstructed.

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