MECHANISM OF LABOUR;
1.
Mechanism of labour is a journey of foetus via
the bony pelvis
2.
With three normal factors like average size baby with good uterine contraction, foetus head
will engage in to the gynecoid pelvis
to the left oblique diameter of the pelvic brim (12cm) engaging diameter of the
foetal head anterio posteriorly is suboccipito frontal (10cm) and transversely
is biperital (9.5cm), were as shoulder will lie right oblique diameter to the pelvic
brim.
3.
Fetus occiput will face the left pectineal line
and face will face the right sacroiliac joint.
4.
Decent
is the continuous process. Increased descend of the foetus due to uterine
contract ion and counter force given by pelvic floor makes fetal head to flex completely. So chin touches the chest of the foetus, that
makes conversion of sub-occipito frontal
diameter into suboccipitobregmatic(9.5cm).
5.
Further descend, counter force of pelvic floor
and completely flexed foetal head makes occiput
to rotate 1/8 to the pelvic
brim internally, so that occiput
will come and lie under the symphysis
pubis , that makes angagement of head occipito anteriorly to the pelvis with
1/8 torsion of neck.
6.
Further descent makes widest biperital diameter
to stretch the pelvic outlet causes crowing.
7.
Further descend makes occiput to slip under the
symphysis pubis and face to sweep the perineam and head will be delivered by
the process of extension.
8.
Foetus head can’t withstand the torsion of the
neck which happened during internal rotation so that the foetus will correct the torsion by making 1/8
rotation of head opposite to internal rotation. So that that torsion will be
relived is called restitution.
9.
Further descend cause shoulder to engage right
oblique diameter to pelvic brim. And head will rotate externally and shoulder will rotate 1/8 internally
that makes anterior shoulder to lie under symphysis pubis. Externally occiput
will face the mothers left thigh and face will see the mother’s right thigh.
10. Further
descend makes anterior shoulder to
expel out by downward and backward flexion and posterior shoulder by upward flexion and forward flexion.
11. Further
descend makes body to deliver by left
and right lateral flexion.
