L4: Labor (Mechanism)

Question 1

Def of Mechanism of Normal Labor

Answer 1

Question 2

Mechanism of Normal Labor

• Steps

Answer 2

• Head
• Shoulders
• Trunk

Question 3

Steps of Delivery of Head

Answer 3

• Descent
• Engagment
• Increased Flexion
• Internal rotation
• Extension
• Restitution
• External Rotation

Question 4

Steps of Delivery of Head

• Descent

Answer 4

Question 5

Descent in Delivery of Head

• Nature of This Process

Answer 5

Continous through the whole process

Question 6

Descent in Delivery of Head

• Causes

Answer 6

a Uterine contraction.
b) Fetal axis pressure.
c) Auxiliary forces of bearing down.

Question 7

Engagement in Delivery of Head

Answer 7

Question 8

Increased Flexion in Delivery of Head

Answer 8

Question 9

Increased Flexion in Delivery of Head

• Causes

Answer 9

• As soon as head meets resistance of pelvic floor, flexion is Incresed, so that chin lies in contact è chest wall.

Question 10

Increased Flexion in Delivery of Head

• Benefits

Answer 10

Question 11

Increased Flexion in Delivery of Head

• Theories

Answer 11

• Lever Theory
• Cylinder Theory
• Pelvic Theory

Question 12

Theories of Increased Flexion in Delivery of Head

• Lever Theory

Answer 12

Question 13

Theories of Increased Flexion in Delivery of Head

• Cylinder Theory

Question 14

Theories of Increased Flexion in Delivery of Head

• Pelvic Theory

Question 15

Internal Rotation in Delivery of Head

Answer 15

Question 16

Internal Rotation in Delivery of Head

• Def

Answer 16

• 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.

Question 17

Internal Rotation in Delivery of Head

• Direction & Degree

Answer 17

• 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°)

Question 18

Internal Rotation in Delivery of Head

• Time

Answer 18

• 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).

Question 19

Internal Rotation in Delivery of Head

• Theories

Answer 19

• Sloping character of pelvic floor
• Pelvic shape theory (rifling action of pelvis)
• Sellheim’s Theory

Question 20

Theories of Internal Rotation in Delivery of Head

• Sloping Pelvic Floor

Answer 20

Question 21

Theories of Internal Rotation in Delivery of Head

• Pelvic Shape Theory (Rifling)

Answer 21

Question 22

Theories of Internal Rotation in Delivery of Head

• Sellheim’s Theory

Question 23

Extension in Delivery of Head

Answer 23

Question 24

Extension in Delivery of Head

• Causes

Answer 24

Question 25

Extension in **Delivery of Head** - Diameters Extending Vulva

Answer 25

- Diameters extending vulva are: SOB, SOF & finally OF diameters (i.e. gradual extension which prevents perineal tears).

Question 26

Restitution in **Delivery of Head**

Answer 26

Question 27

Restitution in **Delivery of Head** - Def

Answer 27

- Movement to undo twist of head on trunk caused by internal rotation (as head rotates anteriorly while shoulders remain in oblique diameter).

Question 28

Restitution in **Delivery of Head** - Direction & Degree

Answer 28

- In opposite direction of internal rotation to bring head at right angle to shoulders again.

Question 29

External Rotation in **Delivery of Head**

Answer 29

Question 30

External Rotation in **Delivery of Head** - Def

Answer 30

- Movement that represents external manifestation of internal rotation of shoulders from oblique diameter of pelvic brim to A-P diameter of outlet.

Question 31

External Rotation in **Delivery of Head** - Direction & Degree

Answer 31

- 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).

Question 32

Steps in **Delivery of Shoulder**

Answer 32

Question 33

Steps in **Delivery of Shoulder** - Descent

Answer 33

Due to the same causes.

Question 34

Steps in **Delivery of Shoulder** - Engagemnet

Answer 34

While head is emerging in A-P diameter of outlet, shoulders engage in oblique diameter of inlet opposite to that traversed by head.

Question 35

Steps in **Delivery of Shoulder** - Internal Rotation

Answer 35

- Anterior shoulder reaches pelvic floor 1st → rotates anteriorly 1/8 circle (in opposite direction of that of head).

Question 36

Steps in **Delivery of Shoulder** - Lateral Flexion

Answer 36

- Anterior shoulder impinges under pubic arch & by lateral flexion of fetal spines, posterior shoulder is born 1st followed by anterior shoulder.

Question 37

Steps in **Delivery of Trunk & Extremities**

Answer 37

Once shoulder is born, the rest of fetus is delivered easily è no special mechanism of labor.