Repro 9: Foetal Growth And Development Flashcards
How does the foetus adapt to its relatively low pO2?
- specialised HbF with higher affinity for O2
- has higher haemotcrit than adults
What is the double Bohr effect?
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
Why is there a lower pCO2 in maternal blood?
Due to progesterone driven hyperventilation
Therefore enables a conc gradient so CO2 can be given up from foetus to mother
What is the double Haldane effect?
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
How does blood bypass the right ventricle (and hence lungs) in foetal circulation?
Via the formamen ovalae
How does blood bypass the lungs in foetal circulation?
Via the ductus arteriosus, which shunts blood from the pulmonary trunk to the aorta
How does blood bypass the liver in foetal circulation?
Via the ductus venosus
How is blood forced through the foramen ovale in a foetus?
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
How does foetal heart rate respond to hypoxia?
Detected by foetal chemoceptors which induce bradycardia (cf in adults which stimulates tachycardia)
What mainly contributes to amniotic fluid volume?
Foetal urine
Foetus swallows some fluid and some bathes the lungs
What is oligohydramnios and what can it indicate?
Too little amniotic fluid volume
Can indicate renal pathology in foetus or poor placental function eg pre-eclampsia
What is polyhydramnios and what can it indicate?
Excess amniotic fluid volume
Can indicate foetus has difficulty swallowing eg oesophageal or duodenal atresia
What is the meconium?
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)
What is amniocentesis?
Sampling at amniotic fluid
Useful for diagnostic testing
How does a foetal handle bilirubin?
Foetus in unable to conjugate bilirubin
It passes across into maternal circulation
But neonate jaundice is common
What is the foetal period?
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
When are pregnancy weeks calculated from?
From the first date of the last menstrual period
I.e. Conception weeks + 2
So term is 40 weeks (although actually 38)
How does foetus growth change in the foetal period?
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
What is the symphysis fundal height?
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
Why is an USS routinely carried out at 20 weeks?
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
What can be used to estimate the foetal age?
- LMP, although inaccurate/ can confuse with bleeding from implantation
- CRL
- Biparietal diameter
- Abdominal circumference and femur length
When is crown rump length used to estimate foetus age?
Most accurate is weeks 7-13
Measure on USS
What is the biparietal diameter?
Distance between the parietal bones of the foetal skull
Used with other measurements in T2 and T3
What is the average birth weight, and what birth weights suggest growth restriction and macrosomia?
3500g average
<2500g suggest growth restriction
>4500g is macrosomia
