MECHANISM OF NORMAL LABOUR

• The lie is longitudinal( longitudinal means relating the length of the fetus)
• The presentation is cephalic(cephalic means associating to the head of the fetus)
• The fetal position left or right occiput anterior position
• The attitude is good flexion(attitude means the position of the part of the baby, normally the fetal head is tucked down and attach to the chest and the arm and legs are drawn towards the centre of the chest that is called flexion.
• The denominator is presenting part and bony landmark to denote position.
• The presenting part is the posterior part of the anterior parietal bone.

Definition

It is the series of movements that occur on the head and the fetal trunk in the process of adaptation, during it’s journey through the pelvis.

Means it is the series of fetal head and trunk movement through the pelvis during labour such as Engagement of head, flexion of head, internal rotation of the head, crowning, extension and birth of head, Restitution, internal rotation of shoulders and external rotation of the head, the birth of. Shoulders and trunk by lateral flexion

STEPS OF MECHANISM OF LABOUR

MAIN MOVEMENTS

Step 1 —Descent

Descent is continue process, due to uterine contraction and retraction ,maternal bearing down effect the fetus descent into mother pelvis.

Step -2 FLEXION

When the fetus presenting part reaches against the pelvic floor increase flexion. Due to flexion there will be smaller presenting diameter subocciput-bregmatic 9.5cm which will negotiate the pelvis easily. But if

slight deflexion occur of the head of the fetus then the presenting diameter is suboccipital frontal 10 cm, it is also normal presenting diameter for delivery.

Step- 3 INTERNAL ROTATION

Due to uterine contraction the fetus descent continue and the leading part pushed downwards on the pelvic floor, when contraction subsides the pelvic floor rebounds causing the occipito to glide forwards. The occiput rotates through 1/8th of the circle(45degree) under the pubic arch

Step-4 CROWNING

crowning occurs when the head visible at vulva and after contraction subsides also the head visible and never go back.

Step-5 EXTENSION

After crowning of the fetal head extends, pivoting around the pubic bone and this releases the sinciput, face, chin, which sweep the perineum and baby head burn by a movement that of extension.

Step-6 RESTITUTION

After the birth of the baby there is noticeable passive movement of the fetal head to correct the twist in the neck due to the internal rotation of the head .and the fetus head turns one eighth of the circle towards the side from which it is started.

Step -7 INTERNAL ROTATION OF SHOULDERS

The anterior shoulder first reach the elevator and muscle and rotates to lie under symphysis pubis, and in same time external rotation of the head occur.

Step-8 BIRTH OF SHOULDERS AND TRUNK

Due descent anterior shoulder releases below the symphasis pubis and due to movement of lateral flexion by the spine posterior shoulder sweeps over the perineum.rest of the trunk is delivered by the lateral flexion

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