Labour Flashcards
What are the boundaries of the pelvic inlet?
anterior = superior pubic rami and upper margin of pubic symphysislateral = iliopectineal lines on each sideposterior = sacral promontory
What occurs in cervical ripening?
decreased collagen productionincreased glycosaminoglycansdecreased aggregation of collagen fibresincrease in inflammatory cells, triggered by prostaglandin production
What must changes must occur in the uterine smooth muscle to facilitate pregnancy?
- cell hypertrophy- increase in glycogen deposition- contractions occur to condition the muscle
What controls uterine smooth muscle contractions?
- oxytocin (increases frequency of action potentials)- prostaglandins (increase in Ca2+ release from intracellular stores)
How are contractions initiated?
Spontaneous depolarisation from pacemakers cells. Depolarisation spreads to each cell via specialised gap junction for coordinated contraction.
What controls the rate of production of prostaglandins?
progesterone to oestrogen ratioincreased P:O ratio causes decreased prostaglandin secretiondecrease P:O ration cause increased prostaglandin synthesis
Describe the Ferguson Reflex
increased stretching in the cervix and vagina causes afferent impulses to be sent to the brain and the hypothalamus stimulates massive oxytocin release from the posterior pituitary, which increases the frequency of the action potentials firing which stimulate the muscle contraction.
What changes occur in the cervix at the start of labour?
- thinning and flattening of cervix- Ferguson reflex- dilation of cervix starts- amnion ruptures
What stages must the fetus go through in order to be delivered?
- head flexes as it reaches the pelvic floor- head internally rotates- flexed head stretches vagina and perineum - head is delivered- head rotates and extends- shoulders rotate to follow the head- shoulders are delivered, followed by the rest of the body
What happens in the third stage of labour?
uterine contractions greatly increase to shear off the placenta and position it in the upper part of the vagina/lower uterine segment. they are expelled within 10 mins
What does the contraction of the uterus in the third stage of labour facilitate?
closes blood vessels and prevents significant bleeding.
What facilitates the strong uterine contraction at the end of the third stage of labour?
an oxytocic drug
Describe how the lungs are established in the newborn
1st breath expends the lungs and reorganises the pulmonary system. blood vessels stretch, so it is easier for them to travel through. have a dramatic decrease in pul. vascular resistance and pulmonary arterial pressure. also LA pressure rises to higher than RA pressure, which closes the foramen ovale.
How is the foramen ovale closed?
reversal of blood flow when LA pressure rises to higher than RA pressure
How is the ductus arteriosus closed?
SM in wall of DA is sensitive to pO2. when the massive increase occurs, this stimulates the smooth muscle to contract. the blood that enters the liver must now pass through the hepatic sinusoids.
How is the neonate assessed once it has been born?
APGAR score0-10assesses colour, tone, pulse, respiration, response of neonate
What stimulates the first breath?
the “trauma” of birth and the relative cold compared to mothers uterus.
What are the characteristics of normal contractions?
3-4 every 10 mins lasting for 60 secs of a moderate or strong amplitude
What must occur before dilation?
effaceent of the cervix– opening up
Describe the process of labour
fetal membranes ruptureuterine musculature become more excitable (P:O ratio)prostaglandins are released (contraction and cervical ripening) contractions cause dilation and stimulate ferguson reflexoxytocin action, pushing fetus down into the birth canal
What makes up the passage that the fetus must pass through?
pelvic inlet (10.5cm)pelvic cavity (12cm)pelvic outlet (11cm)
What can be the cause of labour failing to progress?
Inadequate power- Insufficient uterine contractionInadequate passage- Abnormal bony pelvis- Rigid perineumAbnormalities of the passenger- Fetus is too big- Breech presentation
How is the fetus monitored in labour?
fetal scalp electrode
Describe a cesarean section
suprapubic incisiontransect and resect the linea alba and anterior layers of the rectus sheath superiorly. rectus muscles are divided laterally/though the tendinous part. allows for their reattachment
Give some risks of C-section
bleeding infectiontrauma to vessel, GI tractrisk of anaesthetic
What is operative delivery?
helping the fetus if it is in the incorrect position or mother is significantly tired.
What instruments are used for operative delivery?
forcepsvacuum extraction
How do progesterone levels help throughout pregnancy?
Prevents oxytocin from producing contractions though pregnancy, therefore helps to prevent spontaneous abortion. It also reduces prostaglandin production, therefore reducing the degree of myometrial contraction.
What fetal landmark is used to assess the fetal head position in the birth canal?
fetal fontanelles
What spinal segments are blocked in an epidural?
T9-S4
Why is the patient with an epidural at risk for hypotension?
Lumbar sympathetic outflow blockade prevents vasoconstriction.
Define post-partum haemmorhage
blood loss of greater than 500 ml after vaginal delivery (1000ml in cesarean)
What is the most common cause of post-partum haemmorhage?
uterine atony- loss of muscle tone in uterus, cannot compress blood vessels
What is another common cause of post-partum haemmorhage?
retained placenta
If the uterus is firm on palpation with continuous bleeding, what other cause should you consider?
Laceration or trauma to the genital tract / Retained placenta
What causes Sheehan’s syndrome?
Thrombosis of vessels therefore cutting of the blood supply to the anterior lobe, secondary to severe haemorrhage. This leads to necrosis of the anterior pituitary gland which increases in size during pregnancy, therefore increasing its susceptibility to necrosis.
