Physiology of Pregnancy and Labour

Question 1

Explain what a trophoblast is vs blastocyst?

Answer 1

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.

Question 2

The fertilised ovum progressively divides and differentiates into a ______ as it moves from the site of fertilisation in the upper oviduct to the site ________

Answer 2

blastocyst

of implantation in the uterus

Question 3

Between 3-5 days the blastocyst is _____1________

At 5-8 days the blastocyst _____2______

Answer 3

1) transported into the uterus

2) attaches to the lining of the uterus

Question 4

The inner cells of the blastocyst ___1_____

The outer cells of the blastocyst ___2______

Answer 4

1) are what develops into the embryo

2) burrow into the uterine wall and become placenta (outer cells are collectively called the trophoblast)

Question 5

What happens when the blastocyst adheres to the endometrial lining?

Answer 5

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

Question 6

What is the placenta derived from?

Answer 6

the placenta is derived from both trophoblast and decidual tissue (thick lining of uterus that forms as a result of progesterone)

Question 7

Describe how the placenta develops?

Answer 7

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

Question 8

Describe how the embryo receives nutrition early on before the placenta has developed?

Answer 8

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)

Question 9

Describe transport of oxygen and the placenta?

Answer 9

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

Question 10

The supply of the fetus with oxygen is facilitated by 3 factors which are?

Answer 10

1. Fetal Hb
   (increased ability to carry O2)
2. Higher Hb concentration in fetal blood (50% more than in adults).
3. Bohr effect
   (Fetal Hb can carry more oxygen in low pCO2 than in high pCO2)

Question 11

Describe transport of water across the placenta?

Answer 11

water diffuses into the placenta along its osmotic gradient, exchange increases during pregnancy up to 35th week where it’s 3.5l/ day

Question 12

Describe transport of electrolytes across the placenta?

Answer 12

electrolytes follow H2O, iron and Ca2+ only go mother to child so must make sure the mother has adequate levels

Question 13

Describe transport of glucose across the placenta?

Answer 13

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

Question 14

Describe transport of fatty acids across the placenta?

Answer 14

there is free diffusion of fatty acids

Question 15

Describe transport of waste products across the placenta?

Answer 15

diffusion of waste products is based on concentration gradient

Question 16

Function of HCG?

Answer 16

Human Chorionic Gonadotropin
prevents involution of Corpus Luteum
(CL: stimulates progesterone, estrogen)

effect on the testes of male fetus - development of sex organs

Question 17

Describe levels of HCG in pregnancy?

Answer 17

serum levels double every 48 hours in a singleton early pregnancy
levels fall from 12-14 weeks

Question 18

Describe some instances in which HCG may be abnormal?

Answer 18

ectopic pregnancy (static or slow rising)
failing pregnancy (falling)
ongoing viable pregnancy (doubling or > 60% rise)
molar pregnancy (high levels) 
multiple pregnancy (high levels)

Question 19

Function of HCS/HPL?

Answer 19

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

Question 20

Describe levels of HCS/ HPL through pregnancy?

Answer 20

produced from week 5 and rises throughout

Question 21

Describe levels of progesterone through pregnancy?

Answer 21

rises throughout

Question 22

Function of progesterone?

Answer 22

development of decidual cells

decreases uterus contractility

preparation for lactation

Question 23

Levels of estrogens in pregnancy?

Answer 23

all rise throughout pregnancy, particularly estradiol

Question 24

Function of estrogens in pregnancy?

Answer 24

enlargement of uterus

breast development

relaxation of ligaments (important for labour)

Question 25

Describe some hormonal side effects/ problems in pregnancy?

Answer 25

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

Question 26

What is increased CO due to in pregnancy??

Answer 26

demands of uteroplacental circulation

Question 27

What are all normal CVS exam changes in pregnancy?

Answer 27

ECG changes, functional murmurs and added heart sounds

Question 28

Describe changes in CO, HR and BP in pregnancy?

Answer 28

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

Question 29

Describe haematological changes in pregnancy?

Answer 29

plasma volume increases proportionally with CO (50%) but erthropoesis only by 25% so Hb is decreased by dilution iron requirements increase significantly

Question 30

What are respiratory changes in pregnancy due to?

Answer 30

changes partially due to progesterone and partially due to enlarging uterus interfering with lung function

Question 31

Define tidal volume, vital capacity and minute volume?

Answer 31

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

Question 32

Explain the respiratory changes in pregnancy?

Answer 32

To lower CO2 levels: respiratory rate increases Tidal and minute volume increases (50%) pCO2 decreases slightly Vital capacity and PO2 don’t change

Question 33

Describe urinary changes in pregnancy?

Answer 33

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

Question 34

Describe changes to coagulation in pregnancy?

Answer 34

Pregnancy is a hypercoaguable state | this reduces the risk of haemorrhage during and after delivery but does not increase risk of VTE

Question 35

What is the average weight gain of the mother in pregnancy?

Answer 35

11kg

Question 36

How many extra calories need to be ingested in pregnancy?

Answer 36

200k/cal | 85% fetal metabolism, 15% stored as maternal fat

Question 37

How much protein is needed in pregnancy?

Answer 37

30g/day

Question 38

Describe the two nutritional phases of pregnancy?

Answer 38

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

Question 39

What is insulin resistance in pregnancy caused by?

Answer 39

HPL, cortisol and GH

Question 40

What supplements should be given in pregnancy?

Answer 40

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

Question 41

Define decidual cells?

Answer 41

Decidual cells are a distinctive cell population observed in the mammalian endometrium during pregnancy

Question 42

By what week is the placenta functioning?

Answer 42

5th

Question 43

Define labour?

Answer 43

process whereby the products of conception are expelled from the uterine cavity after the 24th week of gestation

Question 44

Define the first stage of labour?

Answer 44

onset of regular painful contractions and cervical changes until it reaches full dilatation and the cervix is no longer palpable

Question 45

Define the second stage of labour?

Answer 45

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

Question 46

Define the third stage of labour?

Answer 46

duration from the delivery of the newborn to the delivery of the placenta and membranes

Question 47

Describe the physiology of the onset of labour?

Answer 47

it involves progesterone withdrawal and an increase in oestrogen and prostaglandin action mechanisms that regulate these changes aren't fully understood

Question 48

Describe the 3 key factors in labour?

Answer 48

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

Question 49

What are 3 clinical signs of labour onset?

Answer 49

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.

Question 50

What is PROM and ROM?

Answer 50

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

Question 51

What are the 7 cardinal movements of labour?

Answer 51

``` engagement descent flexion internal rotation extension external rotation expulsion ```

Question 52

Describe engagement in labour?

Answer 52

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

Question 53

Describe descent in labour?

Answer 53

downward movement of the presenting part through the pelvis

Question 54

Describe flexion in labour?

Answer 54

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

Question 55

Describe internal rotation in labour?

Answer 55

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

Question 56

Describe extension in labour?

Answer 56

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

Question 57

Describe external rotation (restitution) in labour?

Answer 57

return of the fetal head to the correct anatomical position in relation to the fetal torso and shoulders

Question 58

Describe expulsion in labour?

Answer 58

delivery of the rest of the fetal body

Question 59

Explain what crowning in labour is?

Answer 59

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

Question 60

Describe what happens in the third stage of labour?

Answer 60

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

Question 61

When is a diagnosis of retained placenta made?

Answer 61

if placenta is not expelled within 30 mins if active management or 60 mins if physiological

Question 62

Describe active management of third stage of labour?

Answer 62

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

Question 63

Describe braxton hicks contractions?

Answer 63

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

Question 64

Describe what happens in the puerperium?

Answer 64

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

Question 65

Describe lochia in the puerperium period?

Answer 65

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

Question 66

What may persistence of lochia rubra indicate?

Answer 66

presence of retained placental tissue or fetal membranes