Mechanism Of Labour & Birth

Question 1

What is labour?

Answer 1

Labour is the process by which the fetus, placenta and membranes are expelled through the birth canal

Question 2

What are the four stages of labour?

Answer 2

1. Latent phase
2. First stage
3. Second stage
4. Third stage

Question 3

Define the latent stage of labour

Answer 3

A period of time, not necessarily continuous in which there are contractions and some cervical change, including cervical position, consistency, effacement and dilation up to 4cm

Question 4

Define the first stage of labour

Answer 4

Regular contractions occur, and there is progressive cervical dilation from 4cm

Question 5

Define the second stage of labour

Answer 5

Full dilation of the cervix (10cm) – often determined by vaginal examination

Question 6

Define the third stage of labour

Answer 6

The time from the birth of the baby to the expulsion of the placenta and membranes

Question 7

What are the 4P’s?

Answer 7

POWER - contractions
PASSAGE - cervix
PASSENGER fetus
PSYCHE - hormones

Question 8

What is the mechanism of birth and labour?

Answer 8

1. Descent
2. Flexion
3. Internal rotation (head)
4. Crowning
5. Extension
6. Internal rotation (shoulders)
7. Lateral flexion (shoulders)
8. Birth

Question 9

Define descent

Answer 9

Fetal head moves into pelvis, engagement occurs when widest diameter of PP enters pelvis inlet, more likely to occur before onset of labour in primps, rather than multips

Question 10

Define flexion

Answer 10

At onset of labour, fetal head usually in attitude of natural flexion, flexion increases as the head meets resistance of the pelvic floor, fetal axis pressure transmits through occiput & forehead pushed down further

Question 11

Define internal rotation of the head

Answer 11

When occiput meets resistance of pelvic floor, head rotates forward (approx. 45 degrees), slope of pelvic floor aids internal rotation forwards

Question 12

Define crowning

Answer 12

Occiput escapes under pubic arch & begins to crown, crowning complete when head emerges under pubic arch & no longer recedes between contractions, widest diameter of head is born

Question 13

Define extension

Answer 13

Once crowning is complete, extension completes birth of the head, bregma, forehead, face & chin pass over the perineum

Question 14

Define restitution

Answer 14

Once head is born, the fetus brings it back in line with the shoulders, the baby’s neck is untwisted and there are visible head movements on perineum

Question 15

Define internal rotation of the shoulders

Answer 15

Shoulders undergo rotation (approx. 45 degrees), then lie in AP diameter of pelvic outlet, head rotates externally at the same time – following same direction as restitution

Question 16

Define lateral flexion of the shoulders

Answer 16

Curve of birth canal (curve of carus) causes fetus to flex sideways as it is born, anterior shoulder (under pubic arch) births first, posterior shoulder sweeps over perineum & is birthed

Question 17

Define birth

Answer 17

With gentle traction, remainder of body is born

Question 18

What 3 other systems are affected during birth?

Answer 18

• Cardiovascular system
• Renal system
• Digestive system