10) Birth Flashcards
Define the first stage of labour
Creation of birth canal Onset of labour > Full cervical dilation Latent phase - Onset > ~4cm dilation (slow) Active phase - Faster rate of cervical changes, 1-1.2cm/hour - Regular uterine contractions
Define the second stage of labour
Expulsion of foetus (up to 1hr, can be very fast) Urge to bear down Descended head flexes as it reaches pelvic floor - reduces presentation diameter Internal rotation Head stretches vagina & perineum - risk of tearing, episiotomy Head delivered, head rotates & extends Shoulders rotate & deliver Rest of baby rapidly follows
Define the third stage of labour
Expulsion of placenta
- sheared off by strong contractions of uterus
Contraction of uterus
- compresses blood vessels to reduce haemorrhage
Lasts 5-15 mins
What normal process is necessary to create a birth canal?
Expansion of soft tissues (up to 10cm)
Cervix - At some point of dilation, foetal membranes rupture, releasing amniotic fluid
Vagina
Perineum
Requires structural changes & a lot of force
What determines the size of the birth canal?
Normal presentation, head biggest part - diameter 9.5cm Max size determined by pelvis - pelvic inlet typically 11cm - softening of ligaments may increase this
What is the cervix made of?
Tough, thick collagen
Coiled to give greater structural strength
The cervix needs to soften for birth to occur. What is this called?
Cervical ripening
What is cervical ripening?
Cervix collagen in a proteoglycan matrix
Involves:
Reduction in collagen production (turnover altered)
Increase in glycosaminoglycans (disrupts the matrix)
Reduces aggregation of collagen fibres (uncoils)
What is cervical ripening triggered by?
Prostaglandins
PG E2 & F2x
Locally diffused from uterus
Once released, cervix is ready to be stretched
What happens to the myometrium during cervical ripening?
Smooth muscle, greatly increased in pregnancy
Force generated when intracellular [Ca2+] rises
Due to action potentials (bursts generate sustained contraction)
Triggered spontaneously (pacemakers)
Describe the uterine contractions throughout pregnancy
Progesterone suppresses myometrium’s contraction
Prevents labour occurring until proper time
Early - Low amplitude, every 30 mins
- generally speaking, mother not aware
Late - Higher amplitude, less frequent
- ‘Braxton-Hicks’ contractions
How are the contractions of the uterus made more forceful & frequent?
Prostaglandins (ripen cervix as well) - Increased intracellular [Ca2+] per action potential Oxytocin - More APs - Threshold lowered
What are prostaglandins?
Biologically active lipids, local hormones Produced mainly in endometrium Production controlled by Oestrogen:Progesterone ratio Progesterone>Oestrogen - Low prostaglandins - Throughout pregnancy Oestrogen>Progesterone - Increased prostaglandins - End of pregnancy
Where is oxytocin release from?
Secreted by posterior pituitary (controlled by hypothalamus)
Secretion increased by afferent impulses from cervix & vagina
- Ferguson reflex
- Mechanical stimulation of cervix due to prostaglandins increases oxytocin
Acts on smooth muscle receptors
- More receptors if Oestrogen>Progesterone
What is brachystasis?
Uterine smooth muscle relaxes less than it contracts
Unique feature of uterine smooth muscle
Fibres shorten in body of uterus
Drives presenting part of foetus to cervix
Describe the normal physiological processes which initiate labour
^ foetal cortisol (?)
Oestrogen > Progesterone
^^^ prostaglandins from endometrium of uterus
^ force of uterine contractions
cervix stretched
Oxytocin released from post. pit. (Ferguson reflex)
^ frequency of uterine contractions
Cervix stretched more (+ve feedback, oxytocin release)
What stimuli cause the neonate to take its first breath?
Multiple
Trauma from birth
Cold
How does the foetal cirulation convert to adult circulation?
Reduction in pulmonary vascular resistance
- Blood fills lungs, increased return to LA
- Pressure in LA>RA
- Foramen ovale closes
Increases arterial pO2
- Ductus arteriosus contracts
The condition of a neonate soon after delivery and a few minutes later is scored by what scale?
Apgar score
Assessed 0-10
(5 sections scored 0-2)
What 5 aspects are assessed via the Apgar score?
Appearance (colour) Pulse Grimace (response) Activity (tone) Respiration
How is maternal blood loss limited after birth?
Uterus contracts down hard after birth
Fibres shorten much faster
Placenta sheared off & expelled (within 10mins)
Continued uterine contractions compress maternal blood vessels which ran into placenta
Closed off, reduce haemorrhage
Effect enhanced by giving oxytocic drug
Normal blood flow between mother and placenta is what during pregnancy?
500-800ml/minutes
10-15% Cardiac output
What is the most common foetal presentation?
Baby lies longitudinally
Cephalic presentation, well flexed
Vertex presents to pelvic inlet
Diameter typically 9.5cm
What are the 3 elements of labour? (3 P’s)
Powers
Passage
Passenger
What are the powers involved in labour?
Delivery of foetus dependent on contraction of myometrium (hypertrophy & hyperplasia during pregnancy)
Contraction & retraction of multidirectional smooth muscle fibres cause progressive shortening (particularly fundus & uterus)
How can uterine contractions be assessed?
In terms of frequency, amplitude & duration
What is the passage involved in labour?
Passage formed by bony pelvis & soft tissues
Pelvic Inlet - shorter in antero-posterior plane, 10.5cm diameter
Pelvic Cavity - circular, 12cm diameter
Pelvic Outlet - shorter in medio-lateral plane, 11cm diameter
What movements does the foetus undergo when passing through the birth canal?
Flexes
Extends
Rotates
Who is the passenger involved in labour ;)?
Size & presentation of foetus critical
Orientation of head when entering pelvis, variable
Moulding of cranium may occur - cranial sutures not yet fused
Why might failure of the foetus to progress in labour occur? (Think 3 P’s)
Inadequate power - Insufficient uterine contraction Inadequate passage - Abnormal bony pelvis - Rigid perineum Abnormalities of the passenger - Foetus too big - Foetal (breech) presentation
How can labour be induced?
Give mother prostaglandins & oxytocic drugs
Cause cervix to begin to ripen & uterus begin its contractions
How can foetal heart rate be assessed during labour?
Foetal scalp electrode
What is a Cesarean section?
Suprapubic incision to allow delivery
- Linea alba & anterior layers of rectus sheaths are transected & resected superiorly
- Rectus muscles retracted laterally or divided through their tendinous parts allowing reattachment without muscle fibre injury
What operative deliveries can take place? (Intervention of natural labour)
Forceps
Vacuum extraction
