Fetal Growth And Development Flashcards
What generally happens during the fetal period?
Growth and physiological maturation of the structures created during the embryonic period
Involves preparation for the transition to independent life after birth
When does crown-rump length increase the most?
During the pre-embryonic, embryonic and early fetal period
When is the rate of weight gain at its highest?
Mid and late fetal periods
What is deposited in the early and late fetal periods?
Early - protein deposition
Late - adipose deposition
How much of the lungs does embryonic development produce?
Bronchopulmonary tree
What are the names of the stages of development of the lungs and and which weeks is each one?
Pseudoglandular stage - week 8-16
Canalicular stage - week 16-26
Terminal sac stage - week 26-term
What happens during the pseudoglandular stage? (Week 8-16)
Duct system of the lungs begins to form within the bronchopulmonary segments created during the embryonic period to form bronchioles
What happens in the canalicular stage of development of the lungs (week 16-26)
Formation of respiratory bronchioles
Budding from bronchioles formed during the pseudoglandular stage
What happens during the terminal sac stage of development of the lungs?
Terminal sacs begin to bud from respiratory bronchioles
Get differentiation of type I and II pneumocytes
Surfactant production
How are the lungs prepared for birth during T2 and T3
Breathing movements to condition respiratory musculature
Fluid-filled which is crucial for normal lung development
What is the threshold of viability and when is it?
Viability only possible once lungs have entered the terminal sac stage of development
So after 24 weeks
What is respiratory distress syndrome?
How can you increase fetal surfactant production?
When babies are born pre-maturely, can have insufficient surfactant production
If preterm delivery it is unavoidable, give glucocorticoids to mother to increase fetal surfactant production
What is fetal bradycardia associated with?
Fetal demise
When does fetal kidney function begin?
Week 10
What happens if there is fetal kidney dysfunction?
Oligohydraminos
What can cause oligohydraminos?
Placental insufficiency
Fetal renal impairment
What can cause polyhydraminos?
Fetal abnormality eg inability to swallow
Which system is the first to begin development and last to finish?
Nervous system
When do corticospinal tracts begin to develop and what are they necessary for?
4th month
Required for co-ordinated voluntary movement
When does myelination of the brain begin?
9th month
When is first movement seen?
Week 8
What movements develop during the fetal period?
Suckling
Breathing
Implications of fetal movement?
Noticed by mother from week 17 onwards
Low cost simple method of ante-partum fetal surveillance
Reveals fetuses requiring follow up
Describe the development of the kidneys during the fetal period
Function after ascent is finished in week 10
Renal pelvis and calyces present by week 23
Histological differentiation of cortex and medulla is almost complete by 8 months
What helps in placental transport of carbon dioxide?
Low maternal pCO2 cause by hyperventilation of mother driven by progesterone
If the fetus had an adult’s circulation, what issues would there be?
Loss of oxygen to the liver
Mix with deoxygenated venous blood from the body in the IVC
Mix with deoxygenated blood from the head in the right atrium
Lose oxygen in the lungs leaving desaturated blood for the brain
Where is blood from the umbilical vein delivered to?
The fetal hepatic portal vein
What shunts are present in the fetal circulation?
Ductus venosus to bypass liver
Foramen ovale from IVC directed selectively to left atrium
Ductus arteriosus from pulmonary artery to aorta distal to the branch to the head
For now long does the fetus make breathing movements each day?
1-4 hours
What are lungs filled with in utero?
Amniotic fluid
What is the purpose of amniotic fluid?
Surrounds the fetus to give mechanical protection, provide a moist environment
How much amniotic fluid is there at the different stages of development?
10ml at 8 weeks
1L at 38 weeks
300 ml at 42 weeks
How is amniotic fluid formed?
From maternal fluids and fetal extracellular fluid by diffusion across non-keratinised early on
At 25 weeks and term, how much urine does the fetus produce?
Around 100ml of hypotonic urine a day
About 500ml at term
Cycle of amniotic fluid?
Swallowed by fetus where it absorbs water and electrolytes
Debris accumulates in the fetal gut
Weed out
What does amniotic fluid contain?
Cells from the fetus and amnion and a variety of proteins
What does the debris from the amniotic fluid and fetal gut form?
Meconium
How is bilirubin excreted by the fetus?
Fetus cannot conjugate it so it crosses the placenta and is excreted by the mother
What can an ultrasound scan be used to do?
Calculate age
Rule out ectopic pregnancy
Number of fetuses
Assess fetal growth and abnormalities
When is the ultrasound scan done?
At around 20 weeks
How often does the bladder of the fetus fill and empty?
Every 40-60 mins
What are the factors that affect viability of the pre-term neonate?
Threshold of viability
Brain development - viable only if brain is sufficiently mature to control body function such as breathing
Respiratory distress syndrome
List the techniques used to assess fetal development
Ultrasound scan Doppler ultrasound Non-stress test Biophysical profiles Fetal movements kick chart
What is the non-stress test?
Measures heart rate changes associated with fetal movement
What classes a fetus as having growth restriction?
If weight is less than the tenth percentile for gestational age
What is the difference between symmetrical and asymmetrical growth restriction?
Symmetrical: generalised and proportional
Asymmetrical: abdominal growth lags but relative sparing of head growth
What can cause asymmetrical growth restriction?
Deprivation of nutrition and oxygen supply to fetus
How can the fetal age be estimated?
Duration of pregnancy
Development criteria
Symphysis-fundal height
Which weeks make up the fetal period?
9-38
What are some issues with using the duration of pregnancy as an estimation for the fetal age?
Fertilisation age - use of calendar months may cause inaccuracies
Age since mother’s last menstrual cycle (LMP) - irregular cycles can cause confusion
What are some development criteria for estimating the fetal age and when are some of them used?
Crown-rump length (CRL) used in T1 Foot length Biparietal diameter of head used in T2/3 Weight after delivery Appearance after delivery
What is the symphysis-fundal height?
Can measure distance between pubic symphysis to top of the uterus (fundus) with a tape measure
What are problems with using the symphysis-fundal height?
Multiple fetuses can cause variation
So can volume of amniotic fluid and the lie of the fetus
What are the daily rhythms of the fetus?
Daily rhythms of heart rate, breathing and activity
HR variability is a good index of developing control systems
What are the classifications for birth weights?
4500g = macrosomia (maternal diabetes)
What are the effects of the fetus of poor nutrition in early and late pregnancy?
Early - neural tube defects eg DiGeorge syndrome
In late pregnancy - asymmetrical GR and subsequent oligohydraminos
What is the fetal pO2?
4kPa at most
13.3kPa in adults
Difference between structure of adult and fetal haemoglobin?
Fetal haemoglobin has no beta chains
Therefore does not readily bind 2,3 BPG
How does fetal blood adapt to the low pO2?
Has a higher affinity for oxygen (70% saturated at 4kPa)
Has more haemoglobin
What factors increase oxygen transfer across the placenta?
Low diffusion resistance
Partial pressure gradient (about 9kPa)
High affinity of fetal haemoglobin
What determines the oxygen transport rate across the placenta?
Umbilical arterial pO2
How long would fetal stores of oxygen last for?
2 mins
