Labour And Delivery

Question 1

What is parturition?

Answer 1

Transition from pregnant to non-pregnant state (birth)

Question 2

What is labour?

Answer 2

Physiological process by which a foetus is expelled from the uterus to the outside world

Question 3

What is delivery?

Answer 3

The method of expulsion of the foetus, transforming foetus to neonate

Question 4

What changes (vaguely) are involved in labour?

Answer 4

Involves sequential integrated changes in uterine decidua (internal lining) and myometrium

Changes in the cervix tend to precede uterine contractions.

Question 5

What two things do the contractions during labour need to achieve?

Answer 5

Dilation of the cervix

Pushing the foetus through the birth canal.

Question 6

What happens in the first stage of labour?

Answer 6

Creation of the birth canal and descent of the foetal head into it.
It is the time period between the onset of labour and full dilation of the cervix.

There are two phases:

• Latent: onset of labour with slow cervical dilation but softening. This lasts a variable amount of time.
• Active:Faster rate of change and regular contractions.

Question 7

What happens in the second stage of labour?

Answer 7

Changes in uterine contractions to expulsive, descent of foetus through the birth canal and delivery.

Clinically this is the time between full (10cm) dilation of the cervix and delivery.

There are both passive (descent and rotation of the head) and active (maternal effort to expel the foetus and achieve birth) parts to this.

Question 8

What happens in the third stage of labour?

Answer 8

expulsion of the placenta and contraction of the uterus.

The third stage starts with the completed birth of the baby and ends with the complete expulsion of placenta and membranes.

Usually lasted between 5-15 mins, Up to 30-60 mins may be normal depending on circumstances.

Question 9

How does labour start?

Answer 9

Uterine musculature becomes progressively more excitable

Question 10

Why does labour start?

Answer 10

Prostaglandins promote labour but we don’t know if it is associated with a rise in cortisol like labour is in animals.

Question 11

What are prostaglandins?

Answer 11

Biologically active lipids

Local hormones

Produced mainly in myometrium and decidua

Production controlled by oestrogen:progesterone ration

Question 12

What role do prostaglandins have in labour?

Answer 12

Powerful contractor of smooth muscle and are also involved in cervical softening.

Increase in oestrogen:progesteone ratio and mechanical damage stimulates prostaglandin synthesis.

Placenta, decidua, myometrium and membranes cal all synthesis prostaglandins.

Increased synthesis of prostaglandins by amnion in third trimester.

Levels of prostaglandins in amniotic fund rise very early in labour.

Cervical ripening is due to oestrogen, relaxin and prostaglandins breaking down the connective tissue.

Question 13

What role does progesterone have in labour?

Answer 13

Inhibits contractions - so a fall in progesterone levels facilitates myometrial excitability.

Question 14

What effect does oestrogen have in labour?

Answer 14

Oestrogen increases gap junctional communication between smooth muscle cells - increases contractility.

Question 15

What effect does oxytocin have in labour?

Answer 15

Initiates uterine contractions.

Action inhibited in pregnancy by progesterone, relaxin and low number of oxytocin receptors.

Pregnancy = increased number of gap junctions to aid communication between muscle cells and coordinate uterine activity.

At 36 weeks there is an increased number of oxytocin receptors in the myometrium - therefore the uterus can respond to pulsatile release of oxytocin from the posterior pituitary gland.

Question 16

How oxytocin controlled?

Answer 16

It is secreted by the posterior pituitary and controlled but the hypothalamus.

Question 17

What other factors can help to trigger labour?

Answer 17

Cervical stretching releases prostaglandins.

Foetal effects?

Infection, bleeding - feed into the central mechanisms triggering contractions.

Question 18

How does the cervix change during labour (broadly)?

Answer 18

Cervix retains foetus for most of pregnancy - tough, thick ad made of collagen.

Needs to soften - ‘cervical ripening’ - This will make it soft and open

Question 19

How and why does the cervix rip?

Answer 19

The cervix is made from collagen in a proteoglycan matrix.

Ripening is triggered by prostaglandins (PGE2 and PGF2a) and involves:
-Reduction in collagen 
-Increase in GAGs
Increase in hyaluronic acid 
Reduced aggregation of collagen fibres

Question 20

What cervical changes occur during labour (more detailed)?

Answer 20

The cervix undergoes effacement (thinning) and dilation

Relaxin increases which causes changes in the cervix - collagen ground substance ratio, enzymes degrade collagen.

This occurs over a period of weeks - it is evident from week 36

It means that the labour service offers less resistance to the presenting part.

Question 21

How does the size of the birth canal change?

Answer 21

In a normal presentation the head is the biggest part and the diameter of presentation is 9.5cm.

Maximum size of birth canal is determined by the pelvis - pelvic inlet is typically 11cm but, softening of the ligaments may increase it.

Question 22

How does the pelvic floor, vagina and peineum change?

Answer 22

The stretching of the fibres of the lavator ani and the thinning of the central portion of the perineum transforms to almost transparent membranous structure.

Question 23

How does myometrium help labour?

Answer 23

Contraction and retraction

Myometrial fibres contract but only partially relax. This means that the myometrial muscle does not return to its original size and causes permanent partial shortening of the muscle fibres.

This means that the uterine capacity is progressively reduced so the pressure inside the uterus become stronger and stronger.

Question 24

How is the force generated to push baby out?

Answer 24

The myometrium is much thickened in pregnancy.
Force is generated as the intracellular [Ca2+] rises due to action potentials. It is triggered spontaneously ‘pacemakers’.

Question 25

How do you control contractility?

Answer 25

Contractions are made more forceful and frequent by prostaglandins and oxytocin.

Prostaglandins - more Ca2+ per action potential

Oxytocin - more action potentials as there is a lower threshold.

Question 26

What are some common foetal presentations?

Answer 26

Lie - longitidinal or transverse

Attitude - flexion or extension

Presentation - Breach or not

Question 27

How do you induce labour?

Answer 27

Stimulate release of prostaglandins - membrane rupture

Artificial prostaglandins

Synthetic oxytocin

Anti-progesterone agents

Question 28

How can the physiology of the foetus be monitored during labour?

Answer 28

Monitoring the foetus - compare with obs on any patient - but indirect

Consider the whole picture - the maternal placental-foetal unit

Heart rate patterns

Maternal temperature

Colour and amount of amniotic fluid

Scalp capillary pH

Question 29

What are the three stages of labour?

Answer 29

1 - Creation of birth canal, release of structures which normally retain the foetus in utero, enlargement and realignment of the cervix and vagina.
2- Expulsion of the foetus
3 - Expulsion of the placentaa and changes to minimise blood loss

Question 30

How can delivery be facilitated by intervention?

Answer 30

Cesarian section

Operative delivery (assisted vaginal delivery) - forceps or vacuum extraction

Question 31

What is the normal process used to limit maternal blood loss after delivery?

Answer 31

There is a marked reduction in the size of the uterus due to powerful contractions and ongoing retraction. This put pressure on the site, contraction of the blood vessels and blood clotting mechanism to limit blood loss.

Question 32

What happens after baby is born?

Answer 32

Separation and descent of the placenta

The baby is born and the uterus reduces in size. This therefore means that the placental site is reduced (up to 1/2 before separation begins). The inelastic placenta is then squeezed by contraction.

Question 33

Why is it important to control bleeding?

Answer 33

Normal blood bow is 500-800ml / min. This is 10-15% of cardiac output so, it wouldn’t take very long to loose the entire blood volume.

Question 34

What are the immediate changes in physiology enabling the foetus / neonate to adapt to independent life?

Answer 34

Neonate takes first breath
-Stimuli: Trauma (rub with towel), cold, light, noise

Reduced pulmonary vascular resistance and increased arterial pO2.

Question 35

How does circulation change upon first breath?

Answer 35

1. Clamping of the umbilical cord results in closure of the ductus venosus.
2. On taking the first breath, tissue resistance decreases and blood flows to lungs.
3. Vascular resistance decreases and blood flows to lungs.
4. It becomes oxygenated and pulmonary pO2 rises.
5. Net drop in pressure on the right side of the heart, higher pressure in left atrium closes the foramen ovale.
6. This pressure imbalance results in a temporary reversal of flow through the ductus arteriosus and its muscle wall contracts in response to increased pO2 closing it.

Question 36

How does respiration change after the first breath?

Answer 36

First breath causes lungs to expand
Alveoli inflate
Inflation maintained by surfactant
Regular breathing enabled by neonatal brain pathways triggered at birth

Question 37

What is the Ferguson reflex?

Answer 37

Upon application of pressure to the internal end of the cervix, oxytocin is released which stimulates uterine contractions, which in turn increases pressure on the cervix (thereby increasing oxytocin release, etc.), until the baby is delivered.

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