Repro 9: Foetal Growth And Development

Question 1

How does the foetus adapt to its relatively low pO2?

Answer 1

• specialised HbF with higher affinity for O2

- has higher haemotcrit than adults

Question 2

What is the double Bohr effect?

Answer 2

Promotes O2 exchange to foetus at the placenta because of Bohr effect on maternal and foetal sides, but in opposite directions

At mum, CO2 passes into maternal blood so the pH drops which encourages Bohr effect of Hb to give up O2
Meanwhile at foetus, as it gives up CO2 its pH rises, so the Bohr shift means it has a higher affinity for O2

Question 3

Why is there a lower pCO2 in maternal blood?

Answer 3

Due to progesterone driven hyperventilation

Therefore enables a conc gradient so CO2 can be given up from foetus to mother

Question 4

What is the double Haldane effect?

Answer 4

The fact that as maternal Hb gives up O2, it can more readily accept CO2
Meanwhile as foetal Hb gives up CO2, it can more readily accept O2

Question 5

How does blood bypass the right ventricle (and hence lungs) in foetal circulation?

Answer 5

Via the formamen ovalae

Question 6

How does blood bypass the lungs in foetal circulation?

Answer 6

Via the ductus arteriosus, which shunts blood from the pulmonary trunk to the aorta

Question 7

How does blood bypass the liver in foetal circulation?

Answer 7

Via the ductus venosus

Question 8

How is blood forced through the foramen ovale in a foetus?

Answer 8

As right atria pressure is greater than left atria pressure, so it forces blood through
Also crista dividens tissue directs oxygenated blood towards the foramen ovale

Question 9

How does foetal heart rate respond to hypoxia?

Answer 9

Detected by foetal chemoceptors which induce bradycardia (cf in adults which stimulates tachycardia)

Question 10

What mainly contributes to amniotic fluid volume?

Answer 10

Foetal urine

Foetus swallows some fluid and some bathes the lungs

Question 11

What is oligohydramnios and what can it indicate?

Answer 11

Too little amniotic fluid volume

Can indicate renal pathology in foetus or poor placental function eg pre-eclampsia

Question 12

What is polyhydramnios and what can it indicate?

Answer 12

Excess amniotic fluid volume

Can indicate foetus has difficulty swallowing eg oesophageal or duodenal atresia

Question 13

What is the meconium?

Answer 13

The first foetal faeces
Green in colour due to bile pigments
Should only be released after birth, otherwise it indicates foetal distress
Composed of debris that accumulates in the gut (foetus swallows amniotic fluid, absorbs water and electrolytes and then the debris collects in the gut)

Question 14

What is amniocentesis?

Answer 14

Sampling at amniotic fluid

Useful for diagnostic testing

Question 15

How does a foetal handle bilirubin?

Answer 15

Foetus in unable to conjugate bilirubin
It passes across into maternal circulation
But neonate jaundice is common

Question 16

What is the foetal period?

Answer 16

Stage of intra-uterine life from the end of the eight week until term
Structures that were created in the embryonic period and grow and mature

Question 17

When are pregnancy weeks calculated from?

Answer 17

From the first date of the last menstrual period
I.e. Conception weeks + 2
So term is 40 weeks (although actually 38)

Question 18

How does foetus growth change in the foetal period?

Answer 18

Huge acceleration in growth and weight gain
Early foetus mainly protein deposition
Late foetus mainly adipose deposition
At week 9, head is half CRL whereas body length and limb growth later accelerates

Question 19

What is the symphysis fundal height?

Answer 19

Can palpate the distance between the pubic symphysis and the top of the uterus (fundus) and measure using a tape measure/ comparing position relative to other structures eg umbilicus and xiphisternum

Question 20

Why is an USS routinely carried out at 20 weeks?

Answer 20

As all of the major body systems have formed, so any anomalies can be assessed
It is still early on enough to terminate the pregnancy if necessary

Question 21

What can be used to estimate the foetal age?

Answer 21

• LMP, although inaccurate/ can confuse with bleeding from implantation
• CRL
• Biparietal diameter
• Abdominal circumference and femur length

Question 22

When is crown rump length used to estimate foetus age?

Answer 22

Most accurate is weeks 7-13

Measure on USS

Question 23

What is the biparietal diameter?

Answer 23

Distance between the parietal bones of the foetal skull

Used with other measurements in T2 and T3

Question 24

What is the average birth weight, and what birth weights suggest growth restriction and macrosomia?

Answer 24

3500g average
<2500g suggest growth restriction
>4500g is macrosomia

Question 25

What are the stages of maturation of the respiratory system in a a foetus?

Answer 25

1) pseudoglandular stage
2) canalicular stage
3) terminal sac
4) alveolar period

Question 26

What happens in the pseudoglandular stage of a foetus?

Answer 26

Weeks 8-26
Not viable
No air sacs
Airways have only formed as far as the terminal bronchioles

Question 27

What happens during the canalicular stage in a foetus?

Answer 27

Weeks 16-26
Further branching
Formation of respiratory bronchioles but still no gas exchange

Question 28

What happens in the terminal sac stage of development?

Answer 28

Week 26-term
Terminal sacs bud from respiratory bronchioles
Differentiation of T1 and T2 pneumocytes, hence surfactant is produced from week 20

Question 29

When do the alveoli develop?

Answer 29

In the late foetus stage up until 8 years old

95% of alveoli are formed post-natally

Question 30

What happened to pulmonary resistance at birth?

Answer 30

Pulmonary resistance falls as foetus takes its first breath as alveoli open
This increases blood flow to pulmonary vessels

Question 31

When is a foetus ‘viable’?

Answer 31

Only once the lungs have entered the terminal sac stage

>24 weeks

Question 32

What is respiratory distress syndrome?

Answer 32

Often affects premature infants

Due to insufficient surfactant production (too few T2 pneumocytes)

Question 33

If pre term delivery in unavoidable (eg pre eclampsia), what treatment is given to prevent respiratory distress syndrome of the foetus?

Answer 33

Give the mother steroid (glucocorticoid) treatment, which will increases surfactant production in the foetus

Question 34

What is “quickening”?

Answer 34

When the mother becomes aware of foetal movements from approx 17th week
Free, easy method for foetal assessment

Question 35

How does the CNS develop in the foetus?

Answer 35

First to begin development and last to finish
Corticospinal tracts (required for voluntary movement) begin to form in 4th month
Myelination of brain begins in 9th month