Labour

Question 1

Define term

Answer 1

37-41 weeks of gestation

Question 2

Define pre-term, very pre-term, and extremely pre-term

Answer 2

pre-term: 23-37 weeks of gestation
Very pre-term: 28-32 weeks gestation
Extremely pre-term: <28 weeks

Question 3

What is the definition of labour and what is it range of length

Answer 3

Fundally dominant contraction of the myometrium, coupled with cervical ripening and effacement

12-48 hours

Question 4

Describe the process of labour

Answer 4

1. Cervical ripening and effacement (increasing)
2. Co-ordinated myometrial contractions (increasing)
3. Rupture of fetal membranes
4. Delivery of infant
5. Delivery of placenta
6. Contraction of uterus

Question 5

What are the 3 phases of labour

Answer 5

Phase 1: Uterine contractions and cervical changes

Phase 2: Delivery of the of the foetus

Phase 3 (30 min) : Delivery of the placenta

Question 6

What are the key tissues involved in labour

Answer 6

Cervix, myometrium (uterus) and foetal membranes

The foetal membranes are the fused chorion and amnion

Question 7

What is effacement

Answer 7

The cervix undergoes changes to turn it from rigid to flexible
Effacement is shortening and thinning of cervical walls

Question 8

What are the 3 mechanisms by which effacement occurs

Answer 8

Remodelling of the ECM
Leukocyte recruitment
Inflammation (PGE2 and IL8)

Question 9

Describe uterine contraction during labour

Answer 9

co-ordinated myometrial contraction with fundal dominance
(uterus squeezed from top down)
Increased co-ordination and power

Question 10

What are the key mediators of uterine contraction

Answer 10

Prostaglandin F2 alpha from foetal membranes
Oxytocin receptor activation
CAPs (contraction associated proteins)

Question 11

What is ‘water breaking’ and why does it occur

Answer 11

Rupture of the foetal membranes

Rupture of these membranes happens due to inflammatory changes and membrane remodelling

Question 12

What are the changes that occur during water breaking

Answer 12

Loss of strength due to changes to:
The amnion basement component
Leukocyte recruitment
Increase in inflammatory processes
Increased levels and activity of MMPs

Question 13

What occurs in the third stage of labour

Answer 13

Placental delivery, there are some haemostatic changes that occur here to prevent maternal haemorrhage.

Question 14

What are the haemostatic changes that occur in the third stage of labour

Answer 14

Increased clotting through pregnancy and powerful uterine contraction which will squeeze the maternal blood supply

Question 15

What are the main biochemical factors involved in labour

Answer 15

NFkB
Progesterone and progesterone receptor
Corticotrophin releasing hormone (CRH) and platelet activation factor (PAF)

Question 16

What is the role of NFkB in labour

Answer 16

The is a pro inflammatory transcription factor

Most pro labour genes bind NFkB domains to transcribe mediators involved in labour

Question 17

What is the role of CRH and PAF in labour

Answer 17

PAF is a sign of fetal maturity made by the mature lungs which are the last to develop. It is part of lung surfactant.
CRH and PAF rise before labour and upregulate inflammatory pathways

Question 18

What is the significance of progesterone in pregnancy

Answer 18

Progesterone is needed to sustain pregnancy - Progesterone receptor blockade leads to pregnancy loss
Progesterone levels remain very high until after delivery of the placenta
Effect of progesterone lost in normal term labour

Question 19

What is the difference between the 2 types of progesterone receptor

Answer 19

PR B will mediate progesterone’s effects in pregnancy
PR A reduces its effects

At term PR A: B ratio increases, so you get progesterone withdrawal -> labour

Question 20

What are the causes of pre-term labour

Answer 20

release of CRH, myometrial contraction and inflammation so anything that triggers these 3 factors will cause labour

Stress, twins = increase in CRH
Twins = increase in myometrial contraction
Intra-uterine infection, bleeding = inflammation