Repro: Parturition Flashcards
What is the difference between parturition and labour?
Parturition refers to birth
Labour is the part of parturition when both the cervix and uterus have been remodelled.
Parturition can occur without labour eg elective caesarian
What classes as a ‘pre-term’ and ‘term’ fetus?
Pre-term is before 36 completed weeks. Term is 37-42 weeks.
Before 24 weeks is considered a spontaneous abortion as the fetus is not viable and has no legal rights.
What is the risk of a post-term pregnancy?
(post-term is more than 42 weeks)
Increased risk of fetal death due to ureto-placental insufficiency, aspiration of meconium, macrosomia
At 42 weeks and 6 days the mother is at risk of death due to haemorrhage, infection, obstructed labour.
In UK the labour is induced at 41 weeks 3 days via a drug or rupture of the membranes.
Broadly outline the 3 stages of labour
Stage 1: creation of the birth canal (cervix dilatation to 10cm and effacement)
Stage 2: expulsion of the fetus
Stage 3: expulsion of the placenta
How does the rate of growth of the fetus relate to growth of the placenta?
The fetus and placenta should grow at the same rate. The placenta is weighed after birth and should be the same as the baby, if it is too small, too large or calcified the baby will need extra care.
What assessments of fetal position need to be made towards the end of the pregnancy?
Lie: the relationship of the vertebral column of the fetus compared to the uterus. Usually longitudinal with the fetus in the flexed position.
Presentation: the part of the fetus that is adjacent to the pelvic inlet. Should be the crown, but can be the face, brow, feet (podalic / breech) or shoulder.
Vertex: relationship of fetus along its own axis, head should be 45 degrees from the vertebral column
Why is a shoulder presentation particularly dangerous?
- risk of shoulder distocia, where the shoulders fail to deliver promptly after the head. Risk of brachial plexus injury
- risk of prolapse of the umbilical cord
- risk of impaction, the head will be at one iliac fossa and the bum at the other. With every contraction the fetus gets suffocated. Also risk of uterine rupture
What is the typical diameter of the presentation and the birth canal?
Head is usually 9.5cm and pelvic inlet is 11cm - there is softening of the ligaments esp pubic symphysis which can give some increase.
If presentation is larger than pelvic inlet then emergency C section is needed
What intervention can be used if the cervix is weakened and therefore there is risk of miscarriage of preterm labour?
Cervical cerclage - a tight suture put in and around the cervix to offer additional support
What changes does the cervix undergo in the first stage of labour?
Effacement - the external os lines up with the internal os
Dilatation - from 1mm to 10cm
What substances cause cervical ripening?
- Collagenases reduce collagen content
- Glycosaminoglycans separate the collagen strands to allow the ezymes in
- Increase in hyaluronic acid, expressed when 2 tissues rub together (head and cervix) which causes water influx to expand the tissue
- prostaglandins and oestrogen control the process
What is the definition of clinical labour?
IMPORTANT
3 contractions in every 10 minutes lasting for at least 1 minute each
Outline the uterine contractions throughout pregnancy
Early pregnancy: low amplitude contractions every 30 mins. Not detected
Mid pregnancy: less frequent but higher amplitude. May be detected - “Braxton-Hicks’ contractions. The uterus is preparing for labour to pull the fibres together
Early labour: variable and higher amplitude
Late labour: more frequent and higher amplitude
How do oxytocin and prostaglandins affect contractions?
Oxytocin creates more action potentials by lowering the threshold
Prostaglandins cause more Ca2+ binding per action potential therefore the contractions are stronger
How is the production of prostaglandins controlled?
The oestrogen: progesterone ratio
Oestrogen> progesterone causes increased prostaglandins which is why progesterone rapidly falls in the last month of pregnancy
Outline the ferguson reflex
Stretch receptors in the cervix detect increased pressure which causes more oxytocin to be released which:
- stimulates the uterus to contract
- stimulates the placenta to make prostaglandins, which causes more contractions of the uterus which positively feedbacks to the placenta and the posterior pituitary.
The ovaries secrete oestrogen to increase the oestrogen:progesterone ratio which increases the number of smooth muscle receptors.
What is brachystasis?
The uterus relaxes less than it contracts so the fibres shorten the body of the uterus. Creates a racketing system
At what dilatation does the amnion usually rupture?
Around 2.5cm
How long does the first, second and third stages of labour last?
First stage can last up to 96 hours
Second stage is up to an hour, any longer and the mother is exhausted
Third stage is normally 10 minutes (3 contractions)
What is the term when 1 and 2 feet appear in the birth canal?
1 foot - footling breech
2 feet - double footling breech
Describe the movement of the fetal head during the passage through the birth canal
Initially the head should be flexed (chin on chest)
The head the rotates 45 degrees so the chin is towards the shoulder
The head is delivered and extends so the fetus can pull itself out
The shoulders then rotate and deliver, quickly followed by the rest
This is because the inlet is longer in transverse and the outlet is longer in longitudinal so rotates the baby.
Describe the third stage of labour
The uterus contracts down very hard, causing the placenta to be sheared off and expelled.
Tension is put on the umbilical cord and within 3 contractions (10 minutes) the placenta should be delivered
What is the important effect of contraction of the uterus after parturition?
Compresses the spiral arteries which reduce haemorrhage. This can be enhanced by giving synthetic oxytocin
What causes the baby to take its first breath?
Multiple stimuli such as trauma, cold, light and noise,
Crying shows that this has been achieved - baby must have inhaled to exhale
