Physiology of Pregnancy and Labour Flashcards
Explain what a trophoblast is vs blastocyst?
The blastocyst is a structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast. The trophoblast gives rise to the placenta.
The fertilised ovum progressively divides and differentiates into a ______ as it moves from the site of fertilisation in the upper oviduct to the site ________
blastocyst
of implantation in the uterus
Between 3-5 days the blastocyst is _____1________
At 5-8 days the blastocyst _____2______
1) transported into the uterus
2) attaches to the lining of the uterus
The inner cells of the blastocyst ___1_____
The outer cells of the blastocyst ___2______
1) are what develops into the embryo
2) burrow into the uterine wall and become placenta (outer cells are collectively called the trophoblast)
What happens when the blastocyst adheres to the endometrial lining?
cords of trophoblastic cells begin to penetrate the endometrium
advancing cords of trophoblastic cells tunnel deeper into the endometrium carving out a hole for the blastocyst, the boundaries between cells in the advancing trophoblastic tissue disintegrate
What is the placenta derived from?
the placenta is derived from both trophoblast and decidual tissue (thick lining of uterus that forms as a result of progesterone)
Describe how the placenta develops?
Placenta is derived from both trophoblast & decidual tissue
Trophoblast cells (chorion) differentiate into multinucleate cells (syncytiotrophoblasts) which invade decidua and break down capillaries to form cavities filled with maternal blood
Developing embryo sends capillaries into the syncytiotrophoblast projections to form “placental villi”
Each villus contains fetal capillaries separated from maternal blood by a thin layer of tissue – no direct contact between fetal & maternal blood
2 way exchange of respiratory gases, nutrients, metabolites etc between mother and foetus, largely down diffusion gradient
Placenta (& fetal heart) functional by 5th week of pregnancy
Describe how the embryo receives nutrition early on before the placenta has developed?
Trophoblastic nutrition:
invasion of trophoblastic cells into the decidua
Human chorionic gonadotropin (HCG) signals the corpus luteum to continue secreting progesterone
Progesterone stimulates decidual cells to concentrate glycogen, proteins and lipids (help with healthy implantation and development)
Describe transport of oxygen and the placenta?
the placenta has resp function
O2 diffuses from maternal to fetal circulation as pO2 maternal > PO2 fetal
CO2 follows a reversed gradient
fetal oxygen saturated blood returns to the fetus via the umbilical vein, while maternal, oxygen poor blood flows back into the uterine veins
The supply of the fetus with oxygen is facilitated by 3 factors which are?
- Fetal Hb
(increased ability to carry O2) - Higher Hb concentration in fetal blood (50% more than in adults).
- Bohr effect
(Fetal Hb can carry more oxygen in low pCO2 than in high pCO2)
Describe transport of water across the placenta?
water diffuses into the placenta along its osmotic gradient, exchange increases during pregnancy up to 35th week where it’s 3.5l/ day
Describe transport of electrolytes across the placenta?
electrolytes follow H2O, iron and Ca2+ only go mother to child so must make sure the mother has adequate levels
Describe transport of glucose across the placenta?
glucose is the fetus main source of energy and passes the placenta via simplified transport (high to low concentration), glucose needs are high in 3rd trimester
Describe transport of fatty acids across the placenta?
there is free diffusion of fatty acids
Describe transport of waste products across the placenta?
diffusion of waste products is based on concentration gradient
Function of HCG?
Human Chorionic Gonadotropin
prevents involution of Corpus Luteum
(CL: stimulates progesterone, estrogen)
effect on the testes of male fetus - development of sex organs
Describe levels of HCG in pregnancy?
serum levels double every 48 hours in a singleton early pregnancy
levels fall from 12-14 weeks
Describe some instances in which HCG may be abnormal?
ectopic pregnancy (static or slow rising) failing pregnancy (falling) ongoing viable pregnancy (doubling or > 60% rise) molar pregnancy (high levels) multiple pregnancy (high levels)
Function of HCS/HPL?
Human Placental Lactogen
(Human Chorionic Somatomammotropin)
produced from ~ week 5 of pregnancy
growth hormone-like effects
protein tissue formation.
decreases insulin sensitivity in mother
more glucose for the fetus
involved in breast development in mother during pregnancy
Describe levels of HCS/ HPL through pregnancy?
produced from week 5 and rises throughout
Describe levels of progesterone through pregnancy?
rises throughout
Function of progesterone?
development of decidual cells
decreases uterus contractility
preparation for lactation
Levels of estrogens in pregnancy?
all rise throughout pregnancy, particularly estradiol
Function of estrogens in pregnancy?
enlargement of uterus
breast development
relaxation of ligaments (important for labour)
Describe some hormonal side effects/ problems in pregnancy?
placenta produces CRH which can cause maternal ACTH production which increases cortisol, increases aldosterone which can cause hypertension, oedema, insulin resistance and gestational diabetes
placenta produces HCG which can cause nausea and vomiting, HCG along with HC thyrotropin can also cause hyperthyroidism
Increased Ca2+ demands of pregnancy can cause hyperparathyroidism
What is increased CO due to in pregnancy??
demands of uteroplacental circulation
What are all normal CVS exam changes in pregnancy?
ECG changes, functional murmurs and added heart sounds
Describe changes in CO, HR and BP in pregnancy?
CO is usually 30-50% above normal from about 6 weeks peaking at 24 weeks
CO decreases slightly in last 8 weeks and then increases 30% more during labour
HR increases up to 90bpm to increase CO
BP drops av 15mmHg in 2nd trimester and then rises again
Describe haematological changes in pregnancy?
plasma volume increases proportionally with CO (50%) but erthropoesis only by 25% so Hb is decreased by dilution
iron requirements increase significantly
What are respiratory changes in pregnancy due to?
changes partially due to progesterone and partially due to enlarging uterus interfering with lung function
Define tidal volume, vital capacity and minute volume?
tidal volume: the normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied
minute volume: the amount of air breathed per min
vital capacity: the maximum amount of air a person can expel from the lungs after a maximum inhalation
Explain the respiratory changes in pregnancy?
To lower CO2 levels:
respiratory rate increases
Tidal and minute volume increases (50%)
pCO2 decreases slightly
Vital capacity and PO2 don’t change
Describe urinary changes in pregnancy?
GFR and renal plasma flow increase up to 30-50% peaks at 16-24 weeks
increased reabsorption of ions and water
slight increase of urine formation
Describe changes to coagulation in pregnancy?
Pregnancy is a hypercoaguable state
this reduces the risk of haemorrhage during and after delivery but does not increase risk of VTE
What is the average weight gain of the mother in pregnancy?
11kg
How many extra calories need to be ingested in pregnancy?
200k/cal
85% fetal metabolism, 15% stored as maternal fat
How much protein is needed in pregnancy?
30g/day
Describe the two nutritional phases of pregnancy?
Mother´s anabolic phase:
- normal or increased sensitivity to insulin - lower plasmatic glucose level - lipogenesis, glycogen stores increases - growth of breasts, uterus,weight gain
Catabolic phase (accelerated starvation):
- maternal insulin resistance
- increased transport of nutrients through placental
membrane
- lipolysis
What is insulin resistance in pregnancy caused by?
HPL, cortisol and GH
What supplements should be given in pregnancy?
all women should take 400 mg folic acid for 1st 12 weeks of pregnancy and ideally 3 months before conception to reduce risk of neural tube defects
should take vit D, 10 mg/ day (if BMI> 30 then 20mg/day)
iron supplements may be required
B vitamins to help with erythropoeisis
Define decidual cells?
Decidual cells are a distinctive cell population observed in the mammalian endometrium during pregnancy
By what week is the placenta functioning?
5th
Define labour?
process whereby the products of conception are expelled from the uterine cavity after the 24th week of gestation
Define the first stage of labour?
onset of regular painful contractions and cervical changes until it reaches full dilatation and the cervix is no longer palpable
Define the second stage of labour?
the duration from full cervical dilatation to delivery of the foetus, this is subdivided into a pelvic or passive phase when the head descends into the pelvic and an active or perineal phase when the mother gets a stronger urge to push and the foetus is delivered with the force of the uterine contractions and the maternal bearing down effort
Define the third stage of labour?
duration from the delivery of the newborn to the delivery of the placenta and membranes
Describe the physiology of the onset of labour?
it involves progesterone withdrawal and an increase in oestrogen and prostaglandin action
mechanisms that regulate these changes aren’t fully understood
Describe the 3 key factors in labour?
1) power- uterine contractions
during labour contractions become progressively more frequent, longer lasting and more intense
2) passage- shape or structure of the pelvis
a gynaecoid pelvis is best for childbirth but some women may have anthropoid or android pelvis, these no gynaecoid pelvis are more common in african-caribbean women
3) passenger- fetal lie and presentation are important
What are 3 clinical signs of labour onset?
Regular, painful contractions which increase in frequency and duration and that produce progressive cervical dilatation
The passage of blood-stained mucus from the cervix (the ‘show’) is associated with but not on its own an indicator of onset of labour.
Rupture of membranes can be at the onset of labour but this is variable and can occur without uterine contractions.
What is PROM and ROM?
rom= rupture of membranes
if latent period between rupture of membranes to onset of painful uterine contractions is greater than 4 hours it is called pre labour rupture of membranes PROM
What are the 7 cardinal movements of labour?
engagement descent flexion internal rotation extension external rotation expulsion
Describe engagement in labour?
passage of the widest diameter of the presenting part to a level below the plane of the pelvic inlet, this is described in fifths with the proportion of the fetal head that is unpalpable used as a measure of engagement
Describe descent in labour?
downward movement of the presenting part through the pelvis
Describe flexion in labour?
flexion of the fetal head occurs passively as the head descends due to the shape of the bony pelvis and the resistance offered by the soft tissues
Describe internal rotation in labour?
rotation of the presenting part from its original position (usually transverse with regard to the birth canal) to the anterior position as it passes through the pelvis
Describe extension in labour?
occurs once the foetus has reached the introitus (opening of vagina) and the base of the occiput is in contact to the inferior margin of the pubic symphysis
Describe external rotation (restitution) in labour?
return of the fetal head to the correct anatomical position in relation to the fetal torso and shoulders
Describe expulsion in labour?
delivery of the rest of the fetal body
Explain what crowning in labour is?
crowning refers to the appearance of a large segment of fetal head at the introitus, at this point the labia are stretched to full capacity and the largest diameter of fetal head is encircled by the vulval ring, when crowning you can see the baby’s head coming out the opening of the vagina, crowning usually occurs at extension
Describe what happens in the third stage of labour?
the uterus contracts hardens and rises
umbilical cord lengthens permanently
frequently there is a gush of blood in variable amount
placenta and membranes appear at the introitus
whole process lasts 5-10 mins
When is a diagnosis of retained placenta made?
if placenta is not expelled within 30 mins if active management or 60 mins if physiological
Describe active management of third stage of labour?
most women have active management of the third stage of labour which involves:
uterotonic drugs (e.g. ergometrine maleate or oxytocin)
cord clamping and cutting
bladder catheterisation
active management stops excess bleeding and speeds the process up
a blood loss of less than 500mls is normal in this stage of labour
Describe braxton hicks contractions?
Braxton-Hicks contractions are sometimes called “false labour” because they give the woman a false sensation that she is having real contractions.
Tightening of the uterine muscles, thought to aid the body prepare for birth
Can start 6 weeks into pregnancy but more usually felt in the third trimester
Irregular, do not increase in frequency or intensity
Resolve with ambulation or change in activity
Relatively painless
Describe what happens in the puerperium?
uterine fibres undergo autolysis and atrophy and within 10 days the uterus is no longer palpable abdominally
by end of 6 weeks uterus has largely returned to non pregnant size
the endometrium regenerates within this time if lactation has ceased (if lactation continues menstruation may be delayed for months)
there is discharge from the uterus known as lochia
Describe lochia in the puerperium period?
this refers to discharge from the uterus
at first this consists of fresh or altered blood (lochia rubra) which lasts 2-14 days, then a serous brown discharge (lochia serosa), then a slight white discharge (lochia alba), discharge may persist for 4-8 weeks
What may persistence of lochia rubra indicate?
presence of retained placental tissue or fetal membranes
