Lecture 15: Normal Birth Flashcards
Parturition. What is labour?
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
At what stages can some challenges in Human Parturition manifest?
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
What are the physiological processes in the uterus during pregnancy-birth?
1) Quiescence
2) Activation
3) Stimulation
4) Involution
What are the “anatomical” changes leading to birth?
1) Uterus
(must remain quiet until the end of the pregnancy)- Quiescence
2) Cervix
- Cervical changes
- has to softening, shortening effacement
3) Membrane
- Rupture
How do we maintain quiescence?
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
The hormone responsibble for quiescence is _______
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)
If we wanted to prevent labour what could we do?
Give the patient Progesterone or some form of Ca2+ antagonst.
What is an example of a progesterone antagonist?
e. g. Milfepritone
- Anti-progesterone. blocks progesterone receptor A and B.
- Used to induce labour and is used in medicla abortions
Describe where the Progesterone acts
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
What leads to the initiation of labour in humans>
We don’t know
What factors determine gestation length>
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?
Roughly when do women go into labour?
280 days from Last menstrual period (37-42 weeks)
268 days from conception
Activation of pregnancy involves…..
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
Describe what happens during activation of pregnancy at a cellular level (before you go into labour)
- 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
Name the contraction associated proteins and explain how they work
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
What drugs can be used to counteract Contractility Associated Proteins
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
the final stage of labour is an ______ event drive by ______
the final stage of labour is an inflammatory event drive by prostaglandins
How does PG lead to labour? (3)
1) Increase myometrial contractility
2) Lead to cervix changes
3) Associated with membrane rupture
Is oxytoxin essential for initiation of labour?
No
Roughly describe the processes leading to cervical remodelling
Reaching term (or infection) results in release of lots of cytokines
Also increased collagenolysis
Results in ECM degradation
Results in cervical remodelling (dilatation)
The fetus is wrapped up in what membranes?
Amnion and Chorion
Describe the membranes
- 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
Draw the Summary model of changes during paturition
What happens during birth?
- 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
What are the 3 stages of labour?
1) until full dilatation (10cm)
2) full dilatation until birth of baby
3) from birth of baby until delivery of the placenta
What is a partogram?
We describe labour graphically according to partogram.
Graphic description of labour
Describe the differences in timing of cervical dilatation between different parous
Different cervical dilation at start of active phase
Once the woman is in active phase…….
No medicine will stop the labour.
Describe the first stage of labour
- 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
After birth we must establish……
continous breathing
What happens to the fetus at birth (cardiovascular adaptation)
- 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
What changes occur at birth>
1) Cardiovascular changes (closing of foramen ovale and ductus arteriosus)
2) Establish continous breathing
3) Birth thermogenesis
4) Intermittent nutrition
Describe birth thermogenesis
Non shivering-vascular brown fat
Sympathetic nervous control
Term neonates can maintain body temp to ambient 23 degrees
Describe the Involution phase
- Placental separation
- Cleavage through decidua basalis
- Contractions to p_revent postpartum haemorrhage_
- Increase uterine sensitivity to oxytocin
Summary
Describe the Normal labour mechanisms
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.
