Foetal Physiology And Growth

Question 1

Where are the foetal exchange capillaries located?

Answer 1

Within the chorionic villi

Question 2

What are the only diffusion barrier layers of placenta left by term?

Answer 2

Syncytiotrophoblast

Foetal capillary wall

Question 3

What is the approximate ppO2 of foetal blood?

Answer 3

4 kPa

Question 4

What factors increase foetal oxygen content?

Answer 4

HbF - optimised for hypoxic environment

Foetal haematocrit greater than adults

Question 5

What promotes oxygen exchange to foetus at the placenta?

Answer 5

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

Question 6

What are the subunits of HbF?

Answer 6

2 alpha

2 gamma

Question 7

Why is there a decreased ppCO2 in maternal blood and why is this useful?

Answer 7

Progesterone driven hyperventilation causes blow off more CO2
Conc gradient of CO2 favours CO2 leaving the foetus

Question 8

Which duct allows blood to bypass the liver?

Answer 8

Ductus venosus

Question 9

Why must we bypass the liver in a foetus?

Answer 9

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

Question 10

Describe the foramen ovale in a foetus

Answer 10

Shunt from RA to LA as pressure greater in RA

2 leaves of atrial septum forced apart

Question 11

What is the crista dividens?

Answer 11

Crest on free border of septum secundum

Small specialisation that optimises flow to LA in order to get blood to the brain

Question 12

Why must some blood enter the RV in the foetus?

Answer 12

RV needs pressure to push against in order to develop muscle
And lungs require a small amount of blood to develop

Question 13

What is the role of ductus arteriosus?

Answer 13

Shunts blood from the pulmonary trunk to the aorta

Minimises the drop to oxygen saturation (esp to the brain)

Question 14

What is the foetal response to hypoxia?

Answer 14

Foetal chemoreceptors detect decreased ppO2
Foetal HR slows to reduce oxygen demand
Bradycardia (vagus)

Question 15

Which women are most likely to cause chronic hypoxaemia in their babies?

Answer 15

Women who smoke during pregnancy

Question 16

What are the consequences of chronic hypoxaemia to foetus?

Answer 16

Growth restriction

Behavioural changes eg. Less movements

Question 17

What are the critical hormones for foetal growth and when are they most abundant?

Answer 17

IGF I - T2 and T3 (nutrient dependent)

IGF II - T1 (nutrient independent)

Question 18

What are the functions of the amniotic sac?

Answer 18

Protection

Bathe lungs for development

Question 19

What is the volume of amniotic fluid at 8 weeks?

Answer 19

10 ml

Question 20

What is the volume of amniotic fluid by 38 weeks?

Answer 20

1 litre

Question 21

Urine production of foetus begins at …

Answer 21

9 weeks gestation

Question 22

Approximately how much urine does a foetus produce per day in T3?

Answer 22

Up to 800 ml

Question 23

Describe the composition of amniotic fluid

Answer 23

98% water

Electrolytes, creatinine, urea, bile pigments, renin, glucose, hormones, foetal cells

Question 24

What is vernix caseosa?

Answer 24

Waterproofing of the foetal skin

Prevent damage to skin during extended exposure to AF

Question 25

What is meconium?

Answer 25

First poo of the baby Debris accumulated in the gut with bile = green Should always be passed after delivery

Question 26

Why is it a problem if the meconium is released before birth?

Answer 26

Indicates foetal distress | May inhale it - cause respiratory distress

Question 27

What is amniocentesis?

Answer 27

Sampling of AF Allows for cool action of foetal cells Useful diagnostic test eg. Karyotyping

Question 28

Can a foetus conjugate bilirubin?

Answer 28

No

Question 29

What weeks mark the different stages of development?

Answer 29

1-2 pre-embryonic 3-8 embryonic 9-38 foetal

Question 30

How do we calculate pregnancy weeks?

Answer 30

From first day of last menstrual period Conception weeks + 2 Term = 40 weeks

Question 31

When is the head approximately half CRL?

Answer 31

At 9 weeks

Question 32

At term, how big is the head relative to the whole body length?

Answer 32

1/4

Question 33

Why do we use USS at antenatal assessment?

Answer 33

Safe Used in early pregnancy to calculate age and rule out ectopic Carried out at 20 weeks Estimate growth and look for anomalies

Question 34

When is the crown-rump length most accurate?

Answer 34

Between 7 and 13 weeks

Question 35

What is the biparietal diameter?

Answer 35

Distance between 2 parietal bones of foetal skull | Helping to date pregnancies in T2 and T3

Question 36

Other than BPD, what else can be used for dating foetuses?

Answer 36

Abdominal circumference | Femur length

Question 37

What is the average birth weight?

Answer 37

3.5 kg = 7.7lb

Question 38

Under what weight suggests growth restriction?

Answer 38

< 2.5 kg | < 5.5 lb

Question 39

Over what weight is macrosomia?

Answer 39

> 4.5 kg | > 9.9 lb

Question 40

What are some reasons for low birth weight?

Answer 40

Premature Constitutionally small Growth restriction

Question 41

When does the functional specialisation of the lungs occur?

Answer 41

Foetal period

Question 42

What is occurring between weeks 8 - 16 in the respiratory system?

Answer 42

Pseudoglandular stage | Duct system begins to form within bronchopulmonary segments

Question 43

What happens between weeks 16 - 26 in the respiratory system?

Answer 43

Canalicular stage Formation of respiratory bronchioles - further branching Budding from bronchioles Still no gas exchange membrane

Question 44

What happens between week 26 and term in the respiratory system?

Answer 44

Terminal sac stage Terminal sacs bud from resp bronchioles Membranes for gas exchange Differentiation of Type 1 and 2 pneumocytes

Question 45

Why does the foetus undergo practice breathing movements?

Answer 45

Conditioning of the respiratory musculature | Diaphragm and intercostals

Question 46

What does the amniotic fluid in the lungs do?

Answer 46

Growth factors in the fluid | Encourages type 1 and 2 differentiation

Question 47

What is the threshold of viability of a foetus?

Answer 47

~ 24 weeks +

Question 48

Describe respiratory distress syndrome

Answer 48

Often affects premature babies Insufficient surfactant If unavoidable then give mother glucocorticoids

Question 49

What is the foetal heart rate?

Answer 49

110 - 140 bpm

Question 50

When is a definitive foetal HR achieved?

Answer 50

Week 15

Question 51

What clinical sign would ensue with absent foetal kidney function?

Answer 51

Oligohydramnios

Question 52

What might cause polyhydramnios?

Answer 52

Foetal inability to swallow - structural or neurological

Question 53

When do corticospinal tracts begin to form and what are they for?

Answer 53

4th month | For coordinated voluntary movement

Question 54

When does myelination of the brain begin?

Answer 54

9th month

Question 55

There is no moment in a foetus until ...

Answer 55

Week 8

Question 56

What is quickening?

Answer 56

Maternal awareness of foetal movements Around 17 weeks (May be earlier in subsequent pregnancies)

Question 57

When do gyri and sulci appear in the brain?

Answer 57

~ 28 weeks