Flashcards in Partuition Deck (137):
What is parturition?
The scientific term used to describe the transition from the pregnant state to the non-pregnant state at the end of gestation
How can parturition occur?
Labour or c-section
What is considered to be parturition?
Expulsion of the products of conceptus after 24 weeks
Why must it be after 24 weeks to be considered parturition?
Because 24 weeks is the legal limit of viability
Why is 24 weeks considered the legal limit of viability?
Because after this, the baby can survive outside of the uterus and has legal rights
What is it called when the expulsion of the products of conceptus occurs before 24 weeks?
What is it called when parturition occurs before 36 weeks?
What is pre-term delivery associated with?
Problems with gut and liver
What neurogenic defects can occur with pre-term delivery?
What is considered to be a term delivery?
What is it called when parturition occurs after 42 weeks?
When does death of the fetus occur post-term?
When does death of the mother occur post-term?
42 weeks and 6 days
When are women inducted in the UK?
41 weeks and 3 days
How is labour induction done?
What is labour?
The non-scientific term used to describe parturition when both the cervix and the uterus have been remodelled
Why is the term labour often used instead of parturition?
Because lay people use it
What is actually the case regarding labour and parturition?
It is just one part
What are the stages of labour?
First stage- creation of birth canal
Second stage- expulsion of fetus
Third stage- expulsion of placenta and contraction of uterus
What is the birth canal made up of?
Pelvis and pelvic organs
What happens to the baby and placenta after birth?
They are both weighed to ensure they are roughly the same size
When will paediatrician attention be required following weighing of baby and placenta?
If placenta too large, small, or calcified
What happens to the size of the fetus and uterus during pregnancy?
Increases dramatically (obviously)
When is the uterus palpable in pregnancy?
By about 12 weeks
What is the uterus palpable as at 12 weeks of pregnancy?
Small bump just above pubic symphysis
When does the fetus and uterus reach the umbilicus?
By about 20 weeks
When does the fetus and uterus reach the xiphisternum?
About 36 weeks
What is happening to the position of the fetus at about 36 weeks?
It is starting to turn head downwards
What is fundal height measured as?
Cm from pubic symphysis to uppermost portion of uterus
What is the measurement of fundal height useful for?
To monitor progression of pregnancy
What needs to be assessed towards the end of the pregnancy?
What aspects of fetal position need to be assessed towards the end of pregnancy?
What is meant by fetal lie?
The relationship of the vertebral column to the long axis of the uterus
What should the fetal lie be?
Parallel, with the fetus flexed
What is meant by fetal presentation?
The part that is adjacent to the pelvic inlet
What is the normal fetal presentation?
Crown of the head - termed cephalic
What are the abnormal fetal presentations?
Buttocks - termed podalic, or breech
What is the problem with shoulder presentation?
Dangerous because can cause shoulder dystocia, and can loose baby easily
What is meant by fetal vertex?
The relationship of the fetus along its axis; the orientation of the presenting part in relation to the spinal cord
What is the normal fetal vertex?
About 45 degrees
What is normally true of the vertex to the pelvic inlet?
At minimum diameter
What is the maximum size of the birth canal determined by?
What is the average size of the pelvic inlet?
What is the biggest part in a normal presentation?
What is the diameter of the presentation of the head?
What happens if the babys head is bigger than the canal?
It won't come out, and requires a C-section
What may increase the size of the pelvic inlet?
Softening of the ligaments by collagenases
How is the birth canal created?
By expansion of soft tissues
How much does the perineum expand in the creation of the birth canal?
How are the cervix and vagina stretched to create the birth canal?
What does the creation of the birth canal by expansion of the tissue require?
A lot of force
What is effacement?
The process by which the internal os and external os of the cervix are close together
What is considered early effacement?
30% of the way to fully effaced
What is early effacement caused by?
Little contractions in the ithsmus of the uterus
What is considered to be complete effacement?
When the internal and external os touch
Why does the cervix have to remain closed during pregnancy?
So the products of conception don't fall out
What increases the risk of the products of conception falling out from the cervix during pregnancy?
Previous cervical surgery or cancer
What can be done when there is an increased risk of the products of conception falling out of the cervix during pregnancy?
Put a stitch in
What needs to be true of the cervix to retain the fetus?
Needs to be tough and thick, with lots of collagen
What needs to happen to the cervix in labour?
Needs to undergo softening
What is the softening process of the cervix during labour termed?
What happens in cervical ripening?
Changes in the cervix collagen in proteoglycan matrix
How is the cervix collagen changed in cervical ripening?
Reduction in collagen
Increase in glycosaminoglycans
Increase in hyaluronic acid
What produces a reduction in collagen in cervical ripening?
MMP2 and MMP9 enter the cervix and perform enzymatic degradation
What is the reduction in collagen by MM2 and MMP9 in labour under the influence of?
What is the effect of an increase in glycosaminoglycans in cervical ripening?
Seperates the strands of collagen, and so allow MMP2 and 9 to get into the collagen and break it down further
What is the effect of an increase in hyaluronic acid in the cervix in labour?
Very hydrophilic, so brings water into the tissue, causing it to expand and reducing the aggregation of collagen fibres
What causes an increase in hyaluronic acid in the cervix in labour?
Rubbing of 2 tissues - the cervix against the babies head - causing blistering
What is cervical ripening triggered by?
What prostaglandins trigger cervical ripening?
PGE2 and PGF2-alpha
What generates the force in labour?
What happens to the myometrium in pregnancy?
The smooth muscle becomes much thickened, from 0.5cm to 2.5cm
When are action potentials generated in the myometrium?
When intracellular [Ca] rises due to spontaneous triggering by pacemaker cells in fundus
When do uterine contractions occur in pregnancy?
Describe the uterine contractions in early pregnancy
Low amplitude - some reach threshold and cause a twinge
Every 30 minutes
Describe the uterine contractions in middle pregnancy
Less frequent, higher amplitude, known as 'Braxton-Hicks' contractions
What is happening with Braxton-Hicks contractions?
Uterus is getting ready for labour, and the fibres are coming together to eventually all act as one cell
What is the importance of Braxton-Hicks contractions?
In first pregnancy, might think they are going into labour
Describe the contractions in early labour?
Variable, but high amplitude
What do the contractions in early labour cause?
Increasing pain and backache
Describe the contractions in late labour?
More frequent and higher amplitude
What is clinical labour considered to be?
59 second or more contractions, 3x in 10 minutes
What makes uterine contractions more forceful and frequent?
What effect to prostaglandins have on uterine contractions?
More Ca per action potential
What effect to oxytocin have on uterine contraction?
More action potentials because lower threshold
What are prostaglandins?
Biologically active lipids that act as local hormones
Where are prostaglandins produced?
Mainly in myometrium and decidua
What controls the production of prostaglandins?
What does a low oestrogen:progesterone ratio cause?
What does a high oestrogen:progsterone ratio cause?
When does oestrogen begin to predominate in pregnancy?
When human chorionic gonadotrophin production reduces
What is the result of the relative fall in progesterone when hCG production falls?
It increases prostaglandins, which;
- Ripens cervix
- Promotes uterine contractions
What is oxytocin secreted by?
What is secretion of oxytocin controlled by?
What increases the secretion of oxytocin?
Afferent impulses from the cervix and vagina - the Ferguson reflex
Show the Ferguson reflex
What does oxytocin act on?
Smooth muscle receptors
When are there more oxytocin receptors?
If oestrogen:progesterone ratio is high
What happens to the level of prostaglandins at the onset of labour?
What is the result of the increased prostaglandins at the onset of labour?
Uterine contractions more forceful
What happens in cervical ripening at the onset of labour?
Cervix thins and flattens in process called effacement
Ferguson reflex stimulates oxytocin release
Cervix begins to dilate
Rupture of amnion
How dilated is the cervix by the end of the first stage?
How is cervix dilation measured with fingers?
1 finger = 2.5cm
4 fingers = 10cm
How long does it take for the cervix to be fully dilated?
Can take many hours;
96 hours in first pregnancy
24 hours in previous pregnancies
What happens in brachystasis?
The uterus relaxes less than it contracts
What is the result of the uterus relaxing less than it contracts?
Pulls fibres along their longitudinal axis, driving the presenting part to the cervix
What is created by brachystasis?
A ratcheting system
How is labour initiated in animals?
Rise in oestrogen:progesterone ratio
How is a rise in oestrogen:progesterone ratio bought about in the initiation of labour in animals?
Placenta makes less progesterone, so increased prostaglandins and increased myometrial sensitivity to oxytocin (because more receptors)
How is labour initiated in sheep?
Due to rise in fetal cortisol, which goes to placenta and decreases production of progesterone
Why is looking at sheep labour a good model for what happens in humans?
Because sheep have 1, 2, or 3 lambs
What promotes labour in humans?
Why is the the relationship between progesterone and the initiation of labour in humans unclear?
Humans with no adrenals get born
No consistent evidence of progesterone:oestrogen changes
Evidence that surfactant protein A produced by fetal lungs causes prostaglandin production in myometrium
Why is there no consistent evidence that progesterone:oestrogen changes initiate labour?
Some women have increased progesterone towards the end of pregnancy
How does surfactant protein A stimulate the production of prostaglandins?
It crosses the fetal membranes and stimulates macrophages to produce prostaglandins
How long is the second stage of labour?
Relatively rapid - up to 1 hour, but can be very fast
What does the duration of the second stage of labour depend on?
What is initiated in the second stage of labour?
The urge to 'bear down' and 'push'
Why is the urge to push initiated in the second stage of labour?
Need abdominal muscles to help push out
What appears in the birth canal at the second stage of labour?
The presenting part
What is it called if the presenting part appearing in the birth canal is the top of the head?
What is done once a baby is crowning?
Mother told to push
What is meant by 'breech'?
When the presenting part is buttocks, shoulder, or knee
What must happen if the fetus is breech?
Fetus has to be turned - converted
What is it called when the presenting part is the foot?
What happens to the head of the fetus during the second stage of labour?
It flexes and rotates internally
What does the head of the fetus do to the vagina and perineum?
Stretch it, with a risk of tearing
What can be done if there is a risk of tearing of the perineum?
What complications can arise from epistiotomies?
Fistulae along gut and vagina
What happens once the head has been delivered?
The head rotates and extends, shoulders rotate and deliver, followed rapidly by the rest
What happens to the effect of uterine contractions in the third stage of labour?
It is dramatically increased by expulsion of fetus
What is the result of uterine contractions in the third stage of labour?
The uterus contracts down hard and shears off the placenta to expel it
How long does the third stage of labour normally take?
What is done once the placenta has been expelled?
Wait 3 minutes before clamping it
Why should you wait 3 minutes before clamping the placenta after delivery?
Allows blood to pump to the baby, preventing neonatal jaundice
What is the importance of uterine contractions in the third stage of labour?
Compresses spiral arteries, reducing post-partum haemorrhage