mechanisms of labour

Question 1

what is the first stage of labour

Answer 1

includes both latent and active and is from the onset of labour until cervix is fully dilated (10cm)

Question 2

what is the second stage of labour

Answer 2

includes both passive and active and is from the full dilatation to the birth of the baby

Question 3

what is the third stage of labour

Answer 3

from birth of baby to complete expulsion of placenta an membranes

Question 4

what are the 3 ps

Answer 4

power - involuntary (uterus) and voluntary
passenger - uterine contents - fetus, liquor, cord membranes
passage - pelvis, lower uterine segment, cervix, vagina, pelvic floor muscles

Question 5

what 3 hormonal factors causes labour to commence

Answer 5

maternal, fetal and placental

Question 6

what 2 mechanical factors cause labour to commence

Answer 6

uterine action due to uterine pressure, pressure on cervix

Question 7

what causes labour to commence

Answer 7

complex interaction between hormones that we do not fully understand, and mechanical factors

Question 8

what is DHEA converted to in the placenta

Answer 8

oestrogen

Question 9

what is the placenta stimulated to release

Answer 9

prostaglandins

Question 10

what changes occur to oxytocin receptors

Answer 10

oxytocin receptors in the brain and mammary glands increase

Question 11

what are beta-endorphins

Answer 11

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

Question 12

what is epinephrine

Answer 12

adrenaline

Question 13

what is norepinephrine

Answer 13

noradrenaline

Question 14

what impact can adrenaline have in the early stages of labour

Answer 14

can inhibit labour when the woman doesn’t feel safe

Question 15

what impact can adrenaline have on the later labour

Answer 15

can act on different receptors and stimulate contractions, speeding up the birth

Question 16

what impact does prolactin have during labour

Answer 16

production of prolactin increases in the lining of the uterus near term

Question 17

what 2 factors does cervical dilatation require

Answer 17

uterine action; pressure

Question 18

describe ferguson’s reflec

Answer 18

a positive feedback cycle:
baby presses onto cervix
pressure causes oxytocin to be released
oxytocin causes contractions
contractions push baby down
cycle repeats

Question 19

what changes occur to the pelvic floor to facilitate delivery

Answer 19

becomes flattened and displaced

Question 20

what changes occur to perineal skin during labour

Answer 20

becomes paper thin

Question 21

where do contractions start

Answer 21

in the fundus at the cornua and spreads downwards

Question 22

what does fundal dominance enable

Answer 22

the cervix to dilate + the fundus to push down and expel the fetus

Question 23

describer uterine action in relation to polarity

Answer 23

the upper and lower poles of the uterus work harmoniously - the upper pole contracts strongly and retracts; lower pole contracts slightly and dilates

Question 24

what are the 2 layers of the uterine walls

Answer 24

endometrium
myometrium
perimetrium

Question 25

what 2 layers form the amniotic sac

Answer 25

chorion and amnion

Question 26

which layer of the amniotic sac is closer to the fetus

Answer 26

the amnion

Question 27

what is amniotic fluid made of

Answer 27

urine, lung fluid, skin cells, lanugo - 99% water

Question 28

what is excess amniotic fluid called

Answer 28

polyhydramnios

Question 29

what is reduced amniotic fluid known as

Answer 29

oligohydramnios

Question 30

what is the absence of amniotic fluid known as

Answer 30

anhydramnios

Question 31

describe the forewaters of amniotic fluid

Answer 31

- chorion detaches where cervix dilates - bulges down - presenting part acts like a barrier

Question 32

describe the hindwaters of the amniotic fluid

Answer 32

- the rest of the fluid surrounding the body - cut off from forewaters - where general fluid pressure is exerted

Question 33

why is general fluid pressure useful

Answer 33

fluid is not compressible optimises fetal oxygenation prevents infection maintains constant temp enables lung development

Question 34

what does fetal axis pressure enable

Answer 34

flexion and descent

Question 35

what are the stages of the mechanisms of labour

Answer 35

descent flexion internal rotation crowning of the head extension restituation

Question 36

describe the stage descent

Answer 36

the fetal head descends into the pelvis.

Question 37

what is engagement

Answer 37

when the widest diameter of the head has entered the pelvis

Question 38

describe flexion

Answer 38

as fetus descends, the vertex meets the resistance of the pelvic floor and flexes.

Question 39

what maintains flexion

Answer 39

fetal axis pressure

Question 40

describe internal rotation

Answer 40

once fetal head reaches resistance of pelvic floor, it rotates 45 degrees in the A-P diameter

Question 41

describe crowning

Answer 41

this occurs when the widest diameter of the head emerges under the pubic arch

Question 42

describe extension

Answer 42

extension takes place and the bregma, forehead, face and chin sweep the perineum

Question 43

describe restitution

Answer 43

following delivery of head, the head realigns naturally w/ the shoulders.