7: Foetal Growth & Development Flashcards
When is the foetal period?
From: end of week 8
To: birth
What are the 3 processes of the foetal period?
- Rapid growth (increased cell size + number)
- Continued tissue + organ differentiation
- Relative slow down in growth of head compared to rest of body
When is the embryonic period?
First 8 weeks
What happens in the embyronic period? (3 things)
- Morphogenesis (Crown Rump Length increases rapidly
- Growth @ placenta
- Organogenetic activity
MGO

What does foetal survival depend on in terms of the respiratory system? (2 things)
- Presence of thin-walled air sacs for gas exchange
- Presence of surfactant to reduce surface tension + allow air sac to expand
What are the 4 stages of lung maturation?
- Pseudoglandular (week 8 - 16)
- Canalicular (week 16 - 26)
- Terminal Sac (week 26 - term)
- Alveolar (late foetal - 8 years old)
Puff Cones Till Afterlife

Are the lungs viable in the pseudoglandular stage of lung maturation?
No

Are their air sac in the pseudoglandular stage of lung maturation?
No

Where are the airways formed up to in the pseudoglandular stage of lung maturation?
Ony as far as Terminal Branches

Are the lungs viable in the canalicular stage of lung maturation?
Maybe at end

What is formed in the canalicular stage of lung maturation?
Respiratory bronchioles

What happens in the terminal sac stage of lung maturation? (3 things)
- Terminal sacs bud off from respiratory bronchioles
- Cells differentiate → Type 1 & 2 Pneumocytes (allow diffusion)
- Surfactant produced

What happens in the alveolar stage of lung maturation? (late foetal - 8 years old)
95% of alveoli formed post-natally

What changes occur to the lungs at birth? (4 things)
- Lungs filled with amniotic fluid
- Most is expelled @ vaginal birth and rest is absorbed
- At first breath
- Pulmonary resistance decreases
- Alveoli open
- Blood flow increases in pulmonary vessels
What does placental progesterone promote?
Foetal corticosteroid production (vital for CVS)
When does the foetal thryoid gland begin to work?
Week 12
What do the thyroid hormones help develop? (2 things)
- Hair
- Bone
- CNS
HBC (like HSBC innit)
What does the foetal liver store?
A lot of glycogen
Reflected in changes in foetal abdominal circumference
When is the definitive heart rate acheived?
Week 15
How are heart beats heard in Week 8, Week 12, and Weeks 18 - 20?
Week 8: via Transvaginal US
Week 12: via Doppler Stethoscope
Weeks 18 - 20: via Plain Stethoscope
What is the heart beat at week 8 (measured by transvaginal US) used for?
To rule out ectopic pregnancy
What is the average heart beat at term?
140 - 160 bpm
When is the kidney finished ascending and ready to function?
Week 10
What happens to the kidney at week 10?
Becomes a major contributor to amniotic fluid
What is the route of urine in the foetus? (3 steps)
- Urine enters bladder
- Bladder empties into amniotic fluid
- Amniotic fluid swallowed by foetus
What is the frequency of the bladder emptying and filling?
Every 40-60 minutes
Can be seen on US to asses foetal urinary function
What is oligohydramnios?
Production of too little amniotic fluid
What is oligohydramnios associated with? (2 things)
- Placental insufficiency
- Foetal renal impairments
What is polyhydramnios?
Production of too much amniotic fluid
What is polyhydramnios associated with?
Foetal abnormalities (e.g inability to swallow)
What are the important foetal CNS changes? (5 things)
- Corticospinal tracts (for voluntary movement) formed by month 4
- Brain myelination begins month 9
- Histological differentiation of cortex in cerebrum + cerebellum
- Formation + myelination of nuclei and tracts
- Growth of spinal cord + vertebral column
When can a foetus begin to move?
Week 8
What is quickening, and when does it develop?
Maternal awareness of foetal movements
Develops in week 17
What is clinically important to check in the baby sensory + motor systems? (2 things)
- Viability: if brain mature enough to control body functions (e.g breathing)
- Sensory awareness: pain / sound
What are the biggest factors affecting foetus viability? (2 things)
- Respiratory system
- CNS development
How can foetal / neonate development be assessed? (4 things)
- Crown-Rump Length (CRL) (via US)
- Foot length (via US)
- Biparietal diameter of head
- Weight / appearance after delivering
What are the effects of poor nutrition at Early pregnancy?
Symmetrical growth restriction (growth restriction is generalised and proportional)

What are the effects of poor nutrition at Late pregnancy?
Asymmetrical growth restriction (abdominal growth lags, normal brain growth)

What is poor nutrition of a foetus?
Deprivation of nutrional and oxygen supply to foetus
What is the result of foetal pO2 being lower than adult pO2?
Foetal blood adapts to increase O2 content
What are the adaptations of foetal blood? (3 things)
- Different Hb
- Higher Hb levels
- Efficient diffusion across placenta
How does having different Hb help foetal blood have more oyxgen?
HbF has a higher affinity for O2 than Hb
- HbF is made from 2 alpha + 2 gamma subunits (instead of 2 alpha + 2 beta)
- No beta subunits → 2-3, DGP can’t bind → can’t reduce Hb affinity → affinity stays high
How does having higher Hb levels help foetal blood have more oyxgen?
Carries more O2
How is diffusion across the placenta efficient? (2 things)
- Low diffusion resistance
- High partial pressure gradient
What is the relationship between a foetus and CO2?
Foetus can’t tolerate high CO2
Because it causes problems in acid-base balance
What adaptations ensure foetal CO2 is kept low?
Progesterone → Maternal Hyperventilation → Maternal Hypocapnia → Creates pCO2 gradient between mother and foetus → constant placental transfer of CO2
How is foetal circulation different from adult circulation? (3 things)
- Oxygenated blood enters circulation from placental transfer
- Pulmonary blood flow accounts for less than 20% of total CO (because high pulmonary vasculature resistance)
- 5 foetal vascular structures exists to direct blood flow
What are the 5 foetal structures that direct the blood flow?
- Ductus Arteriosus
- Foramen ovale
- Ductus venosus
- Umbilical Arteries
- Umbilican Vein

What does the Ductus Arteriosus do? (3 things)
- Connects Pulmonary Atery to Aorta
- Shunts blood R → L
- Diverts blood AWAY from lungs

What does the Foramen Ovale do? (3 things)
- Connects 2 atria
- Shunts blood R → L
- Bypasses lungs

What does the Ductus Venosus do? (3 things)
- Receives blood from umbilical vein
- Directs blood to IVC → R atrium
- Bypasses liver

What do the Umbilical Arteries do?
Carry deoxygenated blood to placenta

What does the Umbilical Vein do?
Carries oxygenated blood from placenta

What are the requirements of foetal circulation and how are they met? (2 requirements)
- Higher pressure in R atria than L
* so blood can flow R → L through Foramen Ovale - Higher pressure in Pulmonary Artery than Aorta
* so blood can flow correctly
Both requirements met in foetus because of high flow resistance of lungs
What changes occur at birth to close the shunts?
- Ductus venosus closes as placenta is lost
- Foramen ovale closes when pressure in L atrium exceeds R atrium
* First breath → Resistance in lungs decreases → vessels dilate → R atrium pressure decreases - Ductus arteriosus contracts with increasing pO2 in aorta blood → subsequent contraction of SMC in its walls

What is amniotic fluid?
Fluid surrounding foetus providing:
- Mechanical protection
- Moist environment → protects non K foetal skin
What is the volume of amniotic fluid at:
- 8 weeks
- 38 weeks
- 42 weeks
8 weeks: 10ml
38 weeks: 1L
42 weeks: 300ml
What is the amniotic fluid derived from in early pregnancy? (2 things)
- Dialysis of foetal and maternal EC components
- Exchange across foetal skin (transudation)
What are the cells in amniotic fluid derived from? (2 things)
- Amnion
- Foetus
What is the amniotic fluid derived from in late pregnancy?
Mainly the foetus:
Foetal kidney produces hypotonic urine → forms major part of amniotic fluid
What happens to the urine made by the foetal kidney in late pregnancy?
Swallowed by foetus in constant “cleaning system”
What happens after the foetus swallows the urine?
The foetus absorbs the electrolytes and fluid in the gut
What happens after the foetus absorbs the electrolytes and fluids from the urine in its gut?
Any “debris” remains and accumulates in the gut
This debris is called: Meconium
What is Meconium?
Debris that remains in foetus gut after it has absorbed the fluid + electrolytes from swallowed urine
When is Meconium excreted?
Only in distress
e.g foetal hypoxia
What is amniotic fluid useful for?
Assessing foetal abnormalities
e.g neural tube defects / chromosomal abnormalities
Obtained and assessed by AMNIOCENTESIS
When does foetal insuin begin to be secreted?
Week 10
What creates the concentration gradient for glucose to enter the foetus?
High maternal glucose
What does a foetus use glucose for?
Growth and development
What happens to foetal bilirubin?
Can’t be excreted via gut → so passes across to maternal circulation
Why is jaundice common in neonates?
Neonates can’t immediately deal with bilirubin