Physiology of labour

Question 1

What process causes the cervix to ripen before labour?

Answer 1

Type 1 collagen is degraded by collagenase, collagenase activity is promoted by oestrogen

Question 2

What is the curve of carus?

Answer 2

Angulation of the birth canal

Question 3

What is dystocia?

Answer 3

Difficulty in labour

Question 4

What are the three types of labour dystocia?

Answer 4

Prolonged latent phase (failure of the cervix to ripen)
Primary dysfunctional labour (slow progression of the active phase of labour >!cm/hour
Secondary arrest (failure to progress past 7cm usually due to malpresentation)

Question 5

What are the different types of breech presentation?

Answer 5

Extended or frank (feet by face)- 60-70%
Complete (feet by bottom, knees bent)
footling (feet presenting)

Question 6

Incidence of shoulder dystocia

Answer 6

0.6%

Question 7

Complications of shoulder dystocia

Answer 7

brachial plexus injury 10% -permanent neurological damage 10%
clavicle fracture 15%
Humeral fracture 1%
Asphyxia

Question 8

Recurrence rate of shoulder dystocia

Answer 8

15%

Question 9

What is the normal placental blood flow at term?

Answer 9

500ml/litre

Question 10

When is umbilical cord circulation affected in labour?

Answer 10

During second stage when pushing

Question 11

When do fetal glycogen stores increase?

Answer 11

third trimester in the liver and heart, in preparation for anaerobic respiration during labour

Question 12

What is spalding’s sign?

Answer 12

Overlapping fetal skull bones indicating fetal death - advanced maceration of fetal tissues

Question 13

What happens to progesterone levels prior to parturition?

Answer 13

Falls (approx week 37) - progesterone controls relaxation of the myometrium

Question 14

What happens to oestrogen levels prior to parturition?

Answer 14

oestrogen stays the same but is high relative to progesterone making the uterus more susceptible to oxytocin

Question 15

What does the placenta secrete in preparation for parturition?

Answer 15

relaxin

Question 16

Function of prostaglandin release in labour

Answer 16

Uterus produces prostaglandins in response to contraction - causes softening of the cervix and strengthening contractions

Question 17

What is the vertex?

Answer 17

Presentation of the fetal head in cephalic presentation where the occiput is the leading part