Lecture 15: Normal Birth

Question 1

Parturition. What is labour?

Answer 1

Getting the fetus from the uterus to the outside world

i.e. uterine activity and cervical change which leads to the expulsion of the fetus and placenta

And prevention of haemorrhage so that mother survives, establishing lactation and nurtures the newborn

Question 2

At what stages can some challenges in Human Parturition manifest?

Answer 2

Quiescence: of uterus with growth, distension pressure

Timing: for safe birth

Activation: Stimnulation of uterine masculature changes in genital tract

Birth: Fetal-nonatal adaptations

Involution: Haemostasis, establishing lactation

Question 3

What are the physiological processes in the uterus during pregnancy-birth?

Answer 3

1) Quiescence
2) Activation
3) Stimulation
4) Involution

Question 4

What are the “anatomical” changes leading to birth?

Answer 4

1) Uterus

(must remain quiet until the end of the pregnancy)- Quiescence

2) Cervix
- Cervical changes
- has to softening, shortening effacement
3) Membrane
- Rupture

Question 5

How do we maintain quiescence?

Answer 5

For most of gestation, the uterus contractions exist, but are not synchronised.

Low amplitude and low frequence (“braxton-hicks”). These are painless

The cervix remains firm and closed

The hormone responsibble for quiescence is progesterone

Question 6

The hormone responsibble for quiescence is _______

Answer 6

The hormone responsibble for quiescence is progesterone (also NO)

Progesterone comes from the c_orpus luteum,_

It decreases Ca2+

Withdrawal of 1 or more of the subsances may occur at term. (lead to the uterus not being quiescent)

Question 7

If we wanted to prevent labour what could we do?

Answer 7

Give the patient Progesterone or some form of Ca2+ antagonst.

Question 8

What is an example of a progesterone antagonist?

Answer 8

e. g. Milfepritone
- Anti-progesterone. blocks progesterone receptor A and B.
- Used to induce labour and is used in medicla abortions

Question 9

Describe where the Progesterone acts

Answer 9

Reduce progestoglandin F synthesis

1) FP is responsible for oxytoxin which causes the uterus to contract
2) Also responsible for Calcium transport
3) Also increase Beta adrenergic receptors

Progesterone prevents labour- largely responsible for quiescence

Question 10

What leads to the initiation of labour in humans>

Answer 10

We don’t know

Question 11

What factors determine gestation length>

Answer 11

We don’t know what leads to the intiation of labour.

But Gestation length is determined by…

1) Parity (how many children the mother had previously)

2 Age

3) Genetics-maternal and paternal
4) Race-ethnicity
5) Overall stress?

Question 12

Roughly when do women go into labour?

Answer 12

280 days from Last menstrual period (37-42 weeks)

268 days from conception

Question 13

Activation of pregnancy involves…..

Answer 13

1) Uterine stretch
2) Fetal HPA axis (if the pituitary is undergrown, pregnancy will last longer)
3) Fetal genome
4) Upregulation of myometrium
5) Abnormally if membrane ruptures

Question 14

Describe what happens during activation of pregnancy at a cellular level (before you go into labour)

Answer 14

• Increase in CAPs (contraction associated proteins)- gap junctions
• Prostaglandin receptors increase
• Oxytocin receptors increase

This results in the smooth muscles cells becoming joined together.

So instead of inco-ordinated contractions, and braxton-hix contractions, you get co-ordinated contractions

Question 15

Name the contraction associated proteins and explain how they work

Answer 15

1) These proteins increase the contractility of the myometrium,

Actin myosin

2) Make the muscle more excitable.

Ca2+ voltage regulated

3) Increase intercellular connectivity gap junctions

Multimers of cx43

Question 16

What drugs can be used to counteract Contractility Associated Proteins

Answer 16

1) Clinically antagnoise with Ca channel blockers
- stop increase in myometrial contractility
2) Clinically block B2 sympathomimetics
- stop increase in myocyte excitatbility ion channels
3) Antagonise with PG synthase inhibitors (COX 1 and COX2)
- stop increase in intercellular connectivity gap junctions

Question 17

the final stage of labour is an ______ event drive by ______

Answer 17

the final stage of labour is an inflammatory event drive by prostaglandins

Question 18

How does PG lead to labour? (3)

Answer 18

1) Increase myometrial contractility
2) Lead to cervix changes
3) Associated with membrane rupture

Question 19

Is oxytoxin essential for initiation of labour?

Answer 19

No

Question 20

Roughly describe the processes leading to cervical remodelling

Answer 20

Reaching term (or infection) results in release of lots of cytokines

Also increased collagenolysis

Results in ECM degradation

Results in cervical remodelling (dilatation)

Question 21

The fetus is wrapped up in what membranes?

Answer 21

Amnion and Chorion

Question 22

Describe the membranes

Answer 22

• Amnion and chorion
• Site of PG production
• Rupture not essential for labour
• Rupture at Zone of altered morphology
• Amniotomy in normal labour small effects on progress
• A method of inducing labour

Question 23

Draw the Summary model of changes during paturition

Answer 23

Question 24

What happens during birth?

Answer 24

• Timing right, mature fetus
• Pelvic ligaments softened
• Uterus excitable and contractions are coordinated
• Cervix is soft and easily dilated
• Membranes may rupture- more PGs and possile mechanical benefits

Question 25

What are the 3 stages of labour?

Answer 25

1) until full dilatation (10cm)
2) full dilatation until birth of baby
3) from birth of baby until delivery of the placenta

Question 26

What is a partogram?

Answer 26

We describe labour graphically according to partogram.

Graphic description of labour

Question 27

Describe the differences in timing of cervical dilatation between different parous

Answer 27

Different cervical dilation at start of active phase

Question 28

Once the woman is in active phase…….

Answer 28

No medicine will stop the labour.

Question 29

Describe the first stage of labour

Answer 29

• Contractions
  
  • With each contraction, the pressure increases
  • At a certain stage, the woman will feel pain not pressure
• Cervical effacement and dilatation
• decent of the presenting part
  
  • Spontanoue rupture of membranes
  • Rupture of membranes
  • Premature ROM

Question 30

After birth we must establish……

Answer 30

continous breathing

Question 31

What happens to the fetus at birth (cardiovascular adaptation)

Answer 31

• Closure of foramen ovale
• 100% of Rt ventricle output goes through lungs + Reduction of the pulmonary vascular resistance
• Reduction in presusre results in closure of the ductus arteriosus

Question 32

What changes occur at birth>

Answer 32

1) Cardiovascular changes (closing of foramen ovale and ductus arteriosus)
2) Establish continous breathing
3) Birth thermogenesis
4) Intermittent nutrition

Question 33

Describe birth thermogenesis

Answer 33

Non shivering-vascular brown fat

Sympathetic nervous control

Term neonates can maintain body temp to ambient 23 degrees

Question 34

Describe the Involution phase

Answer 34

• Placental separation
• Cleavage through decidua basalis
• Contractions to p_revent postpartum haemorrhage_
• Increase uterine sensitivity to oxytocin

Question 35

Summary
Describe the Normal labour mechanisms

Answer 35

1) Pregnancy hormones put the b_rake on myometrium_
2) Placental clock in humans (needs intact fetus)
3) An i_nflammatory process_
4) Multiple steps in a cascade - complexity is possibly protective
5) Require interplay between fetus and mother
6) Timing and initiation processes is unknown in humans.