Foetal Physiology And Growth Flashcards
Where are the foetal exchange capillaries located?
Within the chorionic villi
What are the only diffusion barrier layers of placenta left by term?
Syncytiotrophoblast
Foetal capillary wall
What is the approximate ppO2 of foetal blood?
4 kPa
What factors increase foetal oxygen content?
HbF - optimised for hypoxic environment
Foetal haematocrit greater than adults
What promotes oxygen exchange to foetus at the placenta?
Increase maternal 2,3-BPG, decreased affinity of maternal Hb for oxygen
Gradient - lower foetal ppO2
CO2 loss from foetus, pH rise in foetal blood, increasing affinity of HbF for oxygen
What are the subunits of HbF?
2 alpha
2 gamma
Why is there a decreased ppCO2 in maternal blood and why is this useful?
Progesterone driven hyperventilation causes blow off more CO2
Conc gradient of CO2 favours CO2 leaving the foetus
Which duct allows blood to bypass the liver?
Ductus venosus
Why must we bypass the liver in a foetus?
Need to maintain the oxygen saturation for the rest of body
Liver very metabolically active so if passed through first the blood would lose lots of oxygen and nutrients
Describe the foramen ovale in a foetus
Shunt from RA to LA as pressure greater in RA
2 leaves of atrial septum forced apart
What is the crista dividens?
Crest on free border of septum secundum
Small specialisation that optimises flow to LA in order to get blood to the brain
Why must some blood enter the RV in the foetus?
RV needs pressure to push against in order to develop muscle
And lungs require a small amount of blood to develop
What is the role of ductus arteriosus?
Shunts blood from the pulmonary trunk to the aorta
Minimises the drop to oxygen saturation (esp to the brain)
What is the foetal response to hypoxia?
Foetal chemoreceptors detect decreased ppO2
Foetal HR slows to reduce oxygen demand
Bradycardia (vagus)
Which women are most likely to cause chronic hypoxaemia in their babies?
Women who smoke during pregnancy
What are the consequences of chronic hypoxaemia to foetus?
Growth restriction
Behavioural changes eg. Less movements
What are the critical hormones for foetal growth and when are they most abundant?
IGF I - T2 and T3 (nutrient dependent)
IGF II - T1 (nutrient independent)
What are the functions of the amniotic sac?
Protection
Bathe lungs for development
What is the volume of amniotic fluid at 8 weeks?
10 ml
What is the volume of amniotic fluid by 38 weeks?
1 litre
Urine production of foetus begins at …
9 weeks gestation
Approximately how much urine does a foetus produce per day in T3?
Up to 800 ml
Describe the composition of amniotic fluid
98% water
Electrolytes, creatinine, urea, bile pigments, renin, glucose, hormones, foetal cells
What is vernix caseosa?
Waterproofing of the foetal skin
Prevent damage to skin during extended exposure to AF
What is meconium?
First poo of the baby
Debris accumulated in the gut with bile = green
Should always be passed after delivery
Why is it a problem if the meconium is released before birth?
Indicates foetal distress
May inhale it - cause respiratory distress
What is amniocentesis?
Sampling of AF
Allows for cool action of foetal cells
Useful diagnostic test eg. Karyotyping
Can a foetus conjugate bilirubin?
No
What weeks mark the different stages of development?
1-2 pre-embryonic
3-8 embryonic
9-38 foetal
How do we calculate pregnancy weeks?
From first day of last menstrual period
Conception weeks + 2
Term = 40 weeks
When is the head approximately half CRL?
At 9 weeks
At term, how big is the head relative to the whole body length?
1/4
Why do we use USS at antenatal assessment?
Safe
Used in early pregnancy to calculate age and rule out ectopic
Carried out at 20 weeks
Estimate growth and look for anomalies
When is the crown-rump length most accurate?
Between 7 and 13 weeks
What is the biparietal diameter?
Distance between 2 parietal bones of foetal skull
Helping to date pregnancies in T2 and T3
Other than BPD, what else can be used for dating foetuses?
Abdominal circumference
Femur length
What is the average birth weight?
3.5 kg = 7.7lb
Under what weight suggests growth restriction?
< 2.5 kg
< 5.5 lb
Over what weight is macrosomia?
> 4.5 kg
> 9.9 lb
What are some reasons for low birth weight?
Premature
Constitutionally small
Growth restriction
When does the functional specialisation of the lungs occur?
Foetal period
What is occurring between weeks 8 - 16 in the respiratory system?
Pseudoglandular stage
Duct system begins to form within bronchopulmonary segments
What happens between weeks 16 - 26 in the respiratory system?
Canalicular stage
Formation of respiratory bronchioles - further branching
Budding from bronchioles
Still no gas exchange membrane
What happens between week 26 and term in the respiratory system?
Terminal sac stage
Terminal sacs bud from resp bronchioles
Membranes for gas exchange
Differentiation of Type 1 and 2 pneumocytes
Why does the foetus undergo practice breathing movements?
Conditioning of the respiratory musculature
Diaphragm and intercostals
What does the amniotic fluid in the lungs do?
Growth factors in the fluid
Encourages type 1 and 2 differentiation
What is the threshold of viability of a foetus?
~ 24 weeks +
Describe respiratory distress syndrome
Often affects premature babies
Insufficient surfactant
If unavoidable then give mother glucocorticoids
What is the foetal heart rate?
110 - 140 bpm
When is a definitive foetal HR achieved?
Week 15
What clinical sign would ensue with absent foetal kidney function?
Oligohydramnios
What might cause polyhydramnios?
Foetal inability to swallow - structural or neurological
When do corticospinal tracts begin to form and what are they for?
4th month
For coordinated voluntary movement
When does myelination of the brain begin?
9th month
There is no moment in a foetus until …
Week 8
What is quickening?
Maternal awareness of foetal movements
Around 17 weeks
(May be earlier in subsequent pregnancies)
When do gyri and sulci appear in the brain?
~ 28 weeks
