Repro 10: Parturition Flashcards
What is parturition?
The expulsion of the products of conception after 24 weeks (transition from pregnant to non-pregnant state at the end of gestation)
How is labour different to parturition?
Non scientific lay man term
Labour is part of parturition, describes when both the cervix and uterus has been remodelled
Which weeks of gestation classes a baby as being born at term?
37-42 weeks
Spontaneous abortion before 24 weeks, pre term before 36 weeks, and post term after 42 weeks
What briefly happens in each stage of labour?
1st: creation of birth canal
2nd: expulsion of foetus
3rd: expulsion of placenta and contraction of uterus
What should the lie of the foetus be?
Should be longitudinal to the long axis of the uterus
What should the attitude and presentation of the foetus ideally be?
Normally flexed, and in cephalon presentation (head in pelvic inlet)
What is the term used for a foetus in a podalic presentation (feet and buttocks in pelvic inlet)?
Breech
What is the vertex of a foetus?
It’s orientation to the pelvic inlet at minimum diameter, ie head down position ideally 9.5cm
When is the uterus usually first palpable?
Approx 12 weeks
When can the uterus usually be palpated at the xiphisternum?
Approx 36 weeks
What is effacement?
Thinning of the cervix ready to create the birth canal
How is cervical ripening initiated?
Reduction in collagen
Increase in glycosaminoglycans (GAGs which decrease aggregation of collagen fibres)
Increase in hyaluronic acid (hydrophilic so can form blisters)
Increase in NO
What triggers cervical ripening?
Prostaglandins (E2 and F2x)
How does the myometrium generate the force for its contractions?
Increase in intracellular Ca2+ caused by action potentials that can spread from cell to cell, allowing coordinated contractions
Some smooth muscle cells can spontaneously depolarise and act as pacemakers
When do uterine contractions occur in pregnancy?
Occur throughout pregnancy, just start at a low amplitude and increase towards the end (higher amplitude towards the end are Braxton Hicks contractions, which give the impression of false labour)
When in clinically labour defined?
3 contractions last one minute or more, within a 10 minute interval
What initiates the sudden increase in frequency and force of contractions at the onset of labour?
Prostaglandins and oxytocin
Prostaglandins enhance the release of Ca from intracellular stores, oxytocin lowers the threshold to trigger APs
How does the oestrogen: progesterone ratio change to increase prostaglandins?
Oestrogen > progesterone
What is the Ferguson reflex?
Positive feedback mechanism
As sensory receptors in cervix and vagina are stimulated by contractions, excitation passes via afferent nerves to the hypothalamus and promotes more oxytocin release, so contractions become even more more forceful and frequent
Where is oxytocin released from?
The posterior pituitary gland, controlled by the hypothalamus
What is brachystasis?
Describes that with each contraction, the uterus muscle fibres shorten and relax less
So the fundus region shortens progressively which pushes the presenting part of the foetus into the birth canal, stretching the cervix over it
How long does the second stage of labour usually take?
Usually rapid, about 1 hour (up to two hours in primigravida)
How does the position of the foetus change during the second stage of labour?
Presenting part of foetus appears in birth canal (crowning)
Head flexes and rotates internally, then rotates and extends and is delivered
Shoulder rotate and deliver, followed by rest of foetus
What occurs in the third stage of labour?
A powerful uterine contraction shears the placenta and expels it, usually within 10 minutes
Uterus contraction also compressed blood vessels to reduce haemorrhage
