mechanisms of labour Flashcards
what is the first stage of labour
includes both latent and active and is from the onset of labour until cervix is fully dilated (10cm)
what is the second stage of labour
includes both passive and active and is from the full dilatation to the birth of the baby
what is the third stage of labour
from birth of baby to complete expulsion of placenta an membranes
what are the 3 ps
power - involuntary (uterus) and voluntary
passenger - uterine contents - fetus, liquor, cord membranes
passage - pelvis, lower uterine segment, cervix, vagina, pelvic floor muscles
what 3 hormonal factors causes labour to commence
maternal, fetal and placental
what 2 mechanical factors cause labour to commence
uterine action due to uterine pressure, pressure on cervix
what causes labour to commence
complex interaction between hormones that we do not fully understand, and mechanical factors
what is DHEA converted to in the placenta
oestrogen
what is the placenta stimulated to release
prostaglandins
what changes occur to oxytocin receptors
oxytocin receptors in the brain and mammary glands increase
what are beta-endorphins
an endogenous analgesia: thought to have receptors that increase pre-labour and the amount of beta-endorphins increases during labour. these help with stress and pain of labour
what is epinephrine
adrenaline
what is norepinephrine
noradrenaline
what impact can adrenaline have in the early stages of labour
can inhibit labour when the woman doesn’t feel safe
what impact can adrenaline have on the later labour
can act on different receptors and stimulate contractions, speeding up the birth
what impact does prolactin have during labour
production of prolactin increases in the lining of the uterus near term
what 2 factors does cervical dilatation require
uterine action; pressure
describe ferguson’s reflec
a positive feedback cycle:
baby presses onto cervix
pressure causes oxytocin to be released
oxytocin causes contractions
contractions push baby down
cycle repeats
what changes occur to the pelvic floor to facilitate delivery
becomes flattened and displaced
what changes occur to perineal skin during labour
becomes paper thin
where do contractions start
in the fundus at the cornua and spreads downwards
what does fundal dominance enable
the cervix to dilate + the fundus to push down and expel the fetus
describer uterine action in relation to polarity
the upper and lower poles of the uterus work harmoniously - the upper pole contracts strongly and retracts; lower pole contracts slightly and dilates
what are the 2 layers of the uterine walls
endometrium
myometrium
perimetrium
what 2 layers form the amniotic sac
chorion and amnion
which layer of the amniotic sac is closer to the fetus
the amnion
what is amniotic fluid made of
urine, lung fluid, skin cells, lanugo - 99% water
what is excess amniotic fluid called
polyhydramnios
what is reduced amniotic fluid known as
oligohydramnios
what is the absence of amniotic fluid known as
anhydramnios
describe the forewaters of amniotic fluid
- chorion detaches where cervix dilates
- bulges down
- presenting part acts like a barrier
describe the hindwaters of the amniotic fluid
- the rest of the fluid surrounding the body
- cut off from forewaters
- where general fluid pressure is exerted
why is general fluid pressure useful
fluid is not compressible
optimises fetal oxygenation
prevents infection
maintains constant temp
enables lung development
what does fetal axis pressure enable
flexion and descent
what are the stages of the mechanisms of labour
descent
flexion
internal rotation
crowning of the head
extension
restituation
describe the stage descent
the fetal head descends into the pelvis.
what is engagement
when the widest diameter of the head has entered the pelvis
describe flexion
as fetus descends, the vertex meets the resistance of the pelvic floor and flexes.
what maintains flexion
fetal axis pressure
describe internal rotation
once fetal head reaches resistance of pelvic floor, it rotates 45 degrees in the A-P diameter
describe crowning
this occurs when the widest diameter of the head emerges under the pubic arch
describe extension
extension takes place and the bregma, forehead, face and chin sweep the perineum
describe restitution
following delivery of head, the head realigns naturally w/ the shoulders.
