Foetal physiology, growth and development Flashcards
Why does O2 move from mum to baby at the placenta effectively? (5)
- Fetal blood has low pO2- diffusion gradient
- fetal Hb is made of 2 alpha and 2 gamma subunits- higher affinity
- double bohr effect
- increased maternal production of 2,3 BPG secondary to physiological respiratory alkalosis means her Hb is low affinity
- double haldane effect
What is the double bohr effect?
Progesterone= hyperventilation = low pCO2= CO2 entering maternal blood= pH drop= T state= lower affinity for O2= O2 moves to fetus.
Also, CO2 lost from fetal circulation= increase pH= R state= increased affinity for O2
What is the haldane effect?
The Hb in mother gives up more O2 so can accept increasing CO2. Hb on fetus accepts more O2 so gives up Co2. This means no alterations in local pCO2
Describe the fetal circulation
- Most blood in RA passes into LA via foramen ovale
- Some blood however goes into RV, it passes into the pulmonary artery but from here bypasses lungs and goes into aorta via ductus arteriosus
- The blood travels round the body, then goes to the placenta via the umbilical arteries (low pO2)
- Umbillical veins leave placenta, bipasses liver via the ductus venosus and enters back into the IVC
How does the fetus respond to hypoxia? (2)
- Resdistributes blood flow to heart and brain
- Slows down heart rate to reduce O2 demand (chemoreceptors detect drop in pO2 but stimulate rather than inhibit the vagus nerve)
What is a normal HR for a fetus?
120-160 BPM
How can a foetuses HR be measured? (3)
- ultrasound at 5-6 weeks
- doppler stethoscope at 8 weeks
- normal stethoscope at 20 weeks
How much amniotic fluid is normal at 38 weeks?
1L
How is amniotic fluid recycled?
Some is swallowed as it practices swallowing, some is inhaled as it practices breathing, some it absorbed through skin. It is then absorbed and excreted again.
What is amniotic fluid made of?
98% is water. It also contains electrolytes, creatine, urea, bile, renin, glucose, hormones and cells.
What is the vernic caseosa?
A waxy covering which protects the foetuses skin from amniotic fluid.
What happens to debris from swallowng amniotic fluid which cannot be absorbed
It is called muconium, it cannot be directly excreted until birth. It accumulates and in the foetuses GI tract and is passes as its first poo
Which can be done first, choriocentesis or amniocentesis?
choriocentesis
Why do some babies get jaundice after birth?
some times takes a while for their liver to develop the ability to conjugate bilirubin
What hormones are needed for fetal growth, which are specific to the 1st and 2nd trimester?
insulin, EGF, TGFa and leptin (from placenta) always needed.
IDF2 is nutrient independant and seen in trimester 1
IDF1 is nutrient dependant seen in trimester2
What is meant by asymetrical growth restriction?
The baby is disproportionate (head proportionally larger than abdomen)
When does malnutrition have to occur to cause symetrical and asymetrical growth restriction?
If early on= symetrical growth restriction (reversible).
If later= asymetrical
What may cause asymetrical growth restriction?
- maternal factors (malnutrition, smoking ect) later in pregnancy
- Uteroplacental insufficiency (placenta poorly effective
- genetic disorders
- preeclampsia
- preterm birth
What may cause symetrical growth restriction
- extreame fetal malnourishment
- environmental toxins (maternal substance abuse)
- genetic disorders
- congenital infections
- anaemia
- preterm birth
- may just be a small baby (small mum inc likelyhood)
What is the fundal height at 12 weeks, 16 weeks, 20 weeks and 36 weeks?
12 weeks= pubic symphysis
16 weeks= between pubic symphysis and umbilicus
20 weeks= umbilicus
36 weeks= xiphisternum
How does rate and type of growth change?
Embryonic period= hyperplasia, lots of activity but not much absolute growth
Fetal period= hypertrophy and some hyperplasia= lots of absolute growth
Head grows first- taking up 1/2 total body length, eventually the body catches up until head only takes up 1/4 total body length
What should be reported at a normal 20 week scan? (4)
- mother felt baby moving
- heartbeat can be heard w/ normal stethoscope
- structures big enough to be seen w/ ultrasound and check theyre developing normally
- can asses age of fetus accuratly by looking at crown- rump length
Why is time since last menses an inaccurate way to asses fetal age?
Irregular cycles
How can fetal age be assesed in the 2nd or 3rd trimester?
- crown- rump length
- biparietal diameter (distance between the two parietal bones)
Define macro and microsomia
Microsomia= birthweight< 2500g Macrosomia= birthweight > 4000g
What may cause macrosomia?
Gestational diabetes
large parents
constiutionally large
Describe the development of the respiratory system
Starts as diverticulum growing out from foregut at 8-16 weeks. At 16-26 weeks they bud and form bronchioles and the tracheosphageal septum starts to appear. By 26 weeks the respiratory bronchioles appear, the trachea and oesphagus are completely seperated and the type 1 and 2 pneumocytes start to develop.
How can respiratory distress be prevented in babies which have to be born prematurely.
Glucocorticoid treatment before birth, should increase surfacant production
When does the kidney start to develop and what does it do in the foetus?
at the 10th week, it filters urine but doesnt perform other functions of the kidneys
Why is a baby less than 4 months old uncoordinated?
Corticospinal tracts are needed to coordinate voluntary movements but these dont develop till the baby is 4
when does myelination of the brain occur?
In the 9th month of pregnancy
When do motor and sensory systems start to develop?
from 8 weeks, this allows the baby to practise movements such as sucking and breathing. the mother becomes aware of these movements from about 17 weeks
How can fetal development be assessed?
- Amniotic fluid volume (monitors placenta, kidneys, MSK and CNS ect)
- fetal movement (monitors CNS and MSK)
- fetal breathing movements (resp, CNS, MSK)
- heart rate response to non stress test (autonomics, CVS)
What may cause olihydramnios (low amniotic fluid volume)
Placental insufficiency, fetal renal impariment, maternal hypertensive disorders, fetal bladder outlet obstruction, premature rupture of membranes
What may cause polyhydramnios (high amniotic fluid volume)? (2)
inability to swallow, idiopathic
What is normal fetal pO2?
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