Labour And Delivery Flashcards
Define parturition
Parturition = transition from pregnant to non- pregnant state (birth)
Define labour
Labour = physiologic process by which a fetus is expelled from the uterus to the outside world
Define delivery
Delivery = the method of expulsion of the fetus,
transforming fetus to neonate
What are the changes that occurs in labour
- Involves sequential integrated changes in the uterine decidua (internal lining) and myometrium
- Changes in the cervix tend to precede uterine contractions
Describe contraction
- Two major end points – • dilatation of the cervix
* pushing the fetus through the birth canal
What is stage 1
Creation of the birth canal
• Physiologically – multiple changes resulting in
creation of the birth canal and descent of the fetal
head into it
• Clinically – interval between onset of labour and full dilatation of the cervix
• Two phases –
• Latent: Onset of labour with slow cervical dilatation but softening. Lasts a variable time.
• Active: Faster rate of change & regular contractions
What is the second stage
- Physiologically – changes in uterine contractions to expulsive, descent of the fetus through the birth canal and delivery. (adaptations of the fetus)
- Clinically – the time between full (10cm) dilatation of the cervix and delivery.
- passive – descent and rotation of the head
- active –Maternal effort to expel the fetus and achieve birth
What is the 3rd stage
• Physiologically – expulsion of the placenta and contraction of the uterus
• Clinically – third stage starts with the completed birth of the baby and ends with complete expulsion of placenta and membranes
• Usually lasts between 5 and 15 minutes; up to 30 -60 minutes may be normal depending on circumstances
and management
How does labour start?
Uterine musculature becomes progressively more excitable Cervical “ripening” • In humans – Prostaglandins promote labour • So situation is unclear
What are prostaglandins
- Biologically active lipids • Local hormones
- Produced mainly in myometrium and decidua
- Production controlled by oestrogen:progesterone ratio
What are teh fucntions of prstaglandins in labour and what are they synthesised by
- Powerful contractors of smooth muscle and are also involved in cervical softening.
- Increase in oestrogen: progesterone ratio and mechanical damage stimulates prostaglandin synthesis.
- Placenta, decidua, myometrium and membranes can all synthesis prostaglandins
- Increased synthesis of prostaglandins by amnion in third trimester
- Levels of prostaglandins in amniotic fluid rise very early in labour
- Cervical ripening is due to oestrogen, relaxin and prostaglandins breaking down the connective tissue.
What are the roles of progesterone and oestrogen leading up to labour
• Progesterone inhibits contractions
• Oestrogen increases gap junctional communication between smooth muscle cells – increases
contractility
• Mechanical stretching of uterine smooth muscle increases contractility – as gestation increases
Whhat are the role of oxytocin
• Initiates uterine contractions
• Action inhibited in pregnancyo by progesterone, relaxin and low number of oxytocin receptors
• Pregnancy = increased number of gap junctions to aid communication between muscle cells (coordinates effective uterine activity)
• @ 36 weeks = increased number of oxytocin receptors in myometrium - therefore uterus can respond to pulsatile release of oxytocin from
posterior pituitary gland
What is oxytocin secreted by and where does it act
• 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
What are other factories in initiating labour
• Cervical stretching releases prostaglandins
• Fetal effects ? – glucocorticoids – placenta – inhibits
progesterone
• Fetal oxytocin?
• Infection, bleeding – feed into the central mechanisms triggering contractions
What is cervical ripening
• Cervix retains fetus for most of pregnancy
– Tough, thick
– Collagen
• Needs to soften, shorten, open
– ‘cervical ripening’
and open to around 10cm so fetus can i through
How does cervical ripening occurs
• Physiologically • Cervix collagen in proteoglycan matrix • Ripening involves – Reduction in collagen – Increase in glycosaminoglycans – Increases in hyaluronic acid – Reduced aggregation of collagen fibres • Triggered by prostaglandins – PGE2 and PGF2 alpha
What are the changes in the cervix
• Increasing levels of relaxin during pregnancy
• Causes changes in cervix – collagen :
ground substance (gel like substance)
ratio, enzymes degrade collagen
• Occurs over a period of weeks – evident from 36/40
• Labour cervix offers less resistance to presenting part
• Known as effacement and dilatation
What are effacement and dilatation
Ss
What determines the size of the birth canal
• In normal presentation – Head biggest part – Diameter of presentation 9.5 cm • Maximum size of birth canal determined by pelvis – Pelvic inlet typically 11 cm – Softening of ligaments may increase it
What are the soft tissues of the birth canal
• Soft tissues – Cervix – Vagina – Perineum
What are changes to the soft tissue
• The stretching of the fibers of the levator ani and the thinning of the central portion of the perineum transforms to almost transparent membranous structure
Describe the myometrial properties
- Special properties
- Normally muscles contract and relax
- Myometrial fibres contract but only partially relax
- Myometrial muscle does not return to its original size
- Permanent partial shortening of the muscle fibres
- CONTRACTION & RETRACTION
Descrbe how contractions spread
• Symmetry and polarity: the contractions create from two poles of uterus, then go to the fundus and upper part of the uterus, then go down to the lower segment, the forces of the upper segment are more powerful than that of lower segment of uterus.
What is retraction
Retraction: after each contraction the length of each myometrium
muscle of the uterus can not return to the former length, it becomes shorter
and shorter. The uterine
capacity is progressively reduced so the pressure inside uterus becomes stronger and stronger.
Describe the force generated
Myometrium – Much thickened in pregnancy – Force when intracellular [Ca2+] rises – Due to action potentials – Triggered spontaneously • ‘pacemakers’ Ss
Which hormones control contractiilty
Contractions made more forceful and frequent by – Prostaglandins • More Ca2+ per action potential – Oxytocin • More action potentials – Lower threshold Oxytocin has a short half life
What is the lie
Longitudinal lie, parallel to mother axis, transverse, perpendicular to mother axiis
What is the attitude
Neck in flexion or extension
What is the presentation
Head facing upwards. Frank breech most common, can also have full breech or footing breech
What are ways labour can be Induced
- Stimulate release of prostaglandins – membrane rupture
- Artificial prostaglandins
- Synthetic oxytocin
- Anti-progesterone agents
Describe monitoring the fetus
• Monitoring the fetus – compare with observations on any patient – but indirect
• Consider the whole picture – the maternal-placental-
fetal unit
• Heart rate patterns
• Maternal temperature
• Colour & amount amniotic fluid
• Scalp capillary pH
What happens to the fetus in the second stage
• Head hits the elevator ani and flexes
• Head rotates internally
Hits perineum
What happens to the fetus in the second stage
“crowning” – head stretches perineal muscle and skin
- extension of head and external rotation/ restitution
Under pubic symphysis
What is Caesarean section
Abdominal incision. Incise uterus. Push on fundus,
What are methods of assisted vaginal delivery
Forceps, vacuum extraction
Easy to cause injury to mother and/or baby. Easy babies facial nerve can be caught
Vacuum extraction - vacuum cap on baby’s head + maternal effort
Describe the separation and descent f the placenta
- Baby born - marked reduction in size of uterus due to powerful ontraction and retraction (ongoing)
- Size of placental site therefore reduced (can be up to ½ before separation begins)
- Inelastic placenta is squeezed by contraction
Describe the contro of bleeding
- Powerful contraction retraction of uterus especially action of interlacing muscle fibres (“living ligature”) which constrict blood vessels running through the myometrium
- Pressure exerted on placental site by walls of contracted uterus (apposition – once placenta and membranes delivered)
- Blood clotting mechanism (sinuses and torn vessels)
- Normal blood flow through site is 500-800 ml/minute (10-15% of cardiac output)
- Normal physiological processes are critical factors in minimising blood loss and protecting the woman
How is independent lie established
• Neonate takes first breath – Multiple stimuli • Trauma • Cold • Light • Noise • Reduced pulmonary vascular resistance • Increased arterial pO2
Describe respiration initially
- First breath causes lungs to expand
- Alveoli inflate
- Inflation maintained by surfactant
- Regular breathing enabled by neonatal brain pathways triggered at birth
- Resuscitation of newborn based on knowledge of physiology and biochemistry
Decsribe the cicution
1. Clamping the umbilical cord results in closure of the Ductus venosus 2. On taking a first breath, tissue resistance decreases in the lungs 3. Vascular resistance decreases and blood flows to lungs 4. It becomes oxygenated and pulmonary pO2 rises 5. Net drop in pressure on the right side of the heart, higher pressure in left atrium closes Foramen ovale 6. This pressure imbalance results in a temporary reversal of flow through the Ductus arteriosus and its muscle wall contracts in response to increased pO2 closing it
