Parturition Flashcards
What is labour?
Expulsion of products of conception after 24 weeks:
- Spontaneous abortion - before 24 weeks
- Pre-term - before 37 weeks
- Term - 37-42 weeks
Parturition
What are the stages of labour?
First stage - Creation of birth canal Second stage - Expulsion of fetus Third stage - Expulsion of placenta - Contraction of uterus
Describe the change in size of things over pregnancy.
Fetus, placenta, uterus increase dramatically in size
- Uterus palpable by 12 weeks
- Reaches umbilicus c20 weeks
- Xiphisternum by 36 weeks
What needs to be assessed towards the end of pregnancy?
'Lie' - Relationship to long axis of uterus - Normally longitudinal - Fetus normally flexed 'Presentation' - Which part is adjacent to pelvic inlet - Normally head (cephalic) - Sometimes buttocks (podalic) (also known as a breach) 'Position' - Orientation of presenting - Most commonly; - Longitudinal lie - Cephalic presentation - Vertex to pelvic inlet at minimum diameter
Tell me about the size of the birth canal.
In normal presentation: - Head biggest part - Diameter of presentation 9.5cm Maximum size of birth canal determined by pelvis - Pelvic inlet typically 11cm - Softening of ligaments may increase it
Tell me about the creation of the birth canal.
Expansion of soft tissues: - Cervix - Vagina - Perineum - To about 10cm Needs - Structural changes - A lot of force
What are the structural changes associated with the creation of the birth canal?
Cervix retains fetus for most of pregnancy - Tough, thick - Collagen Needs to soften - 'Cervical ripening'
Describe cervical ripening.
Cervix collagen in proteoglycan matrix Ripening involves: - Reduction in collagen - Increase in glycosaminoglycans - Reduces aggregation of collagen fibres Triggered by prostaglandins - PG E2 and F2x
How is the force generated to create the birth canal, and to give birth?
Myometrium
- Smooth muscle
- Much thickened in pregnancy
- Force when intracellular [Ca2+] rises
- Due to action potentials (burst of action potentials)
- Triggered spontaneously
- ‘Pacemakers’
Tell me about uterine contractions.
Occur throughout pregnancy
- Early
- Low amplitude, every 30 min
- Late
- Less frequent
- Higher amplitude
- ‘Braxton-Hicks’ contractions
How is contractibility controlled in pregnancy?
Contractions are made more forceful and frequent by:
- Prostaglandins
- More Ca2+ per action potential
- Oxytocin
- More action potentials
- Lower threshold
- More action potentials
What are prostaglandins? (in relation to pregnancy)
Biologically active lipids Local hormones Produced mainly in endometrium Production controlled by oestrogen progesterone ratio: - Low (progesterone>oestrogen) - Low prostaglandins - High (oestrogen >progesterone) - Increased prostaglandins
What happens when there is a relative fall in progesterone?
Increases prostaglandins
- Ripen cervix
- Promote uterine contractions
Tell me about oxytocin.
Secreted by posterior pituitary
Controlled by hypothalamus
Increased by afferent impulses from cervix and vagina
- ‘Ferguson reflex’
Acts on smooth muscle receptors
- More receptors if oestrogen/progesterone ratio high
Tell me about the onset of labour.
More prostaglandins
- Cervix ripens
- Uterine contractions more forceful
- Brachystasis
- Uterus relaxes less than contracts
- Fibres shorten in body of uterus
- Drives presenting part to cervix
Tell me about the changes in the cervix towards onset of labour.
Cervix thins and flattens
- ‘Effacement’
Ferguson reflex stimulates Oxytocin release
- Contractions more forceful and more frequent
Cervix begins to dilate
Rupture of the amnion
- ‘breaking of the waters’
How wide is the cervix at the end of the first stage?
Cervix dilated to 10cm
May take many hours
Tell me about the initiation of labour.
Prostaglandins promote labour BUT - Fetuses with no adrenals get born - No consistent evidence of progesterone oestrogen changes So situation is unclear
Tell me about the second stage of labour.
Relatively rapid
- Up to 1hr but can be very fast
Urge to ‘bear down’ - to use abdominal muscles
Presenting part appears in birth canal
Head rotates internally Head stretches vagina and perineum - Risk of tearing - Episiotomy Head delivered Heads rotates and extends Shoulders rotate Shoulders deliver Followed rapidly by rest
Tell me about the third stage of labour.
Effect of uterine contractions dramatically increased by expulsion of fetus Uterus contracts down hard Shears of placenta And expel it Normally within 10 minutes
What is the importance of uterine contractions?
When the placenta is sheered off a lot of blood vessels are sheered open as well
Compresses blood vessels
Reduce haemorrhage
Enhanced by giving oxytocic drug
Tell me about establishing independent life after birth.
Neonate takes first breath - Multiple stimuli - Trauma - Cold Reduces pulmonary vascular resistance Increases arterial pO2
Left atrial pressure exceeds right
- Foramen ovale closes
Ductus arteriosus contracts in response to raised pO2
Fetal converts to adult circulation
