L4: Labor (Mechanism) Flashcards
Def of Mechanism of Normal Labor
Mechanism of Normal Labor
- Steps
- Head
- Shoulders
- Trunk
Steps of Delivery of Head
- Descent
- Engagment
- Increased Flexion
- Internal rotation
- Extension
- Restitution
- External Rotation
Steps of Delivery of Head
- Descent
Descent in Delivery of Head
- Nature of This Process
Continous through the whole process
Descent in Delivery of Head
- Causes
a Uterine contraction.
b) Fetal axis pressure.
c) Auxiliary forces of bearing down.
Engagement in Delivery of Head
Increased Flexion in Delivery of Head
Increased Flexion in Delivery of Head
- Causes
- As soon as head meets resistance of pelvic floor, flexion is Incresed, so that chin lies in contact è chest wall.
Increased Flexion in Delivery of Head
- Benefits
Increased Flexion in Delivery of Head
- Theories
- Lever Theory
- Cylinder Theory
- Pelvic Theory
Theories of Increased Flexion in Delivery of Head
- Lever Theory
Theories of Increased Flexion in Delivery of Head
- Cylinder Theory
Theories of Increased Flexion in Delivery of Head
- Pelvic Theory
Internal Rotation in Delivery of Head
Internal Rotation in Delivery of Head
- Def
- Rotation of head on its vertical axis around wall of pelvis so that longitudinal diameter of head is gradually carried to occupy A-P diameter of pelvic outlet.
Internal Rotation in Delivery of Head
- Direction & Degree
- In OA, head rotates forwards 1/8 circle (sagittal suture rotates from oblique diameter to A-P diameter while shoulders remain in opposite oblique diameter so, neck undergoes twist of 45°)
Internal Rotation in Delivery of Head
- Time
- It takes place usually during 2nd stage (it starts to occur when head occupies plane of greatest pelvic dimension & meets resistance of sloping pelvic floor).
Internal Rotation in Delivery of Head
- Theories
- Sloping character of pelvic floor
- Pelvic shape theory (rifling action of pelvis)
- Sellheim’s Theory
Theories of Internal Rotation in Delivery of Head
- Sloping Pelvic Floor
Theories of Internal Rotation in Delivery of Head
- Pelvic Shape Theory (Rifling)
Theories of Internal Rotation in Delivery of Head
- Sellheim’s Theory
Extension in Delivery of Head
Extension in Delivery of Head
- Causes
Extension in Delivery of Head
- Diameters Extending Vulva
- Diameters extending vulva are: SOB, SOF & finally OF diameters (i.e. gradual extension which prevents perineal tears).
Restitution in Delivery of Head
Restitution in Delivery of Head
- Def
- Movement to undo twist of head on trunk caused by internal rotation (as head rotates anteriorly while shoulders remain in oblique diameter).
Restitution in Delivery of Head
- Direction & Degree
- In opposite direction of internal rotation to bring head at right angle to shoulders again.
External Rotation in Delivery of Head
External Rotation in Delivery of Head
- Def
- Movement that represents external manifestation of internal rotation of shoulders from oblique diameter of pelvic brim to A-P diameter of outlet.
External Rotation in Delivery of Head
- Direction & Degree
- It is continuation of restitution & it is in the same direction (head rotates another 1/8 circle in the same direction of restitution → occiput becomes direct lateral in position facing maternal thigh).
Steps in Delivery of Shoulder
Steps in Delivery of Shoulder
- Descent
Due to the same causes.
Steps in Delivery of Shoulder
- Engagemnet
While head is emerging in A-P diameter of outlet, shoulders engage in oblique diameter of inlet opposite to that traversed by head.
Steps in Delivery of Shoulder
- Internal Rotation
- Anterior shoulder reaches pelvic floor 1st → rotates anteriorly 1/8 circle (in opposite direction of that of head).
Steps in Delivery of Shoulder
- Lateral Flexion
- Anterior shoulder impinges under pubic arch & by lateral flexion of fetal spines, posterior shoulder is born 1st followed by anterior shoulder.
Steps in Delivery of Trunk & Extremities
Once shoulder is born, the rest of fetus is delivered easily è no special mechanism of labor.
