mechanism of labor

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.