What is happening in the pre-embryonic period?
Lots of cell division
When is the pre-embryonic period?
What happens in the embryonic period?
Growth and physiological maturation of the structures created during the embryonic period
When is the embryonic period?
What is the embryonic period the stage of?
Greatest morphological change
What is the embryonic period characterised by?
Intense activity, as it is the organogenic period
What is meant by the organogenic period?
Building detailed stuctures from a few cells
How much absoloute growth is there in the embryonic period?
What is the fetal period?
The period involving preperation for the transition to independant life after birth
When is the fetal period?
What is being grown towards in the fetal period?
The ability to survive after delivery
What happens to the rate of growth and weight gain in the fetal period?
How do the body proportions change in the fetal period?
At 9 weeks, the head is approx half of the crown-rump length, but thereafter the body length and limb growth accelerate, becasue development is in a head-to-tail fashion
When does crown-rump length increase rapidly?
In the pre-embryonic, embryonic, and early fetal period
What happens to weight gain throughout gestation?
It is slow at first, and then increases rapidly in the mid- and late-fetal periods
How much weight gain is there in the embryo?
Little weight gain, placental growth is most significant, and constitutes a large % of the weight gain
What is responsible for the weight gain in the early fetus?
Protein deposition to build the growing muscles
What is responsible for the weight gain in the late fetus?
What is the importance of adipose deposition in the late fetus?
Prepares it for life after the uterus
Why is adipose deposition required for life after the uterus?
Helps manage body temperature
What happens in an ante-natal assessment of fetal wellbeing?
- Mother asked about fetal movements
- Regular measurements of uterine expansion
- Ultrasound scans
Why is it useful to ask the mother about fetal movements?
Mother will come to know the rhythm of the movements that the baby takes, and so can detect if their is a change
How is uterine expansion measured?
Symphysis-fundal height measured by palpation of pubic symphysis and fundus of uterus
Why are ultrasounds used in pregnancy rather than x-rays?
Because they are safe, and we don't want to do anything that can damage the vulnerable fetus
What can ultrasound scans be used for in early pregnancy?
- Calculate age
- Rule out ectopic pregnancies
- Check number of fetuses
- Check fetal heart rate
Why is it important to check the fetal heart rate in early pregnancy?
Because fetal bradycardia can be a sign of impending fetal demise
When are ante-natal ultrasounds routinely performed?
What is being looked for at the 20 week ultrasound?
Why can fetal anomalies be assessed at a 20 week ultrasound?
All major body systems have grown, so there are no further structural changes
What systems can be assessed at the 20 week ultrasound?
- Brain ventricles
- Heart chambers
- Spinal cord development
Why is it important to check for spinal cord development at the 20 week ultrasound?
Look for signs of spina bifida
How can fetal age be estimated?
- Developmental criteria
How is fetal age calculated from LMP?
Find out date of 1st day of LMP. and estimate ovulation from normal cycle length
What is the problem with calculating fetal age from LMP?
Prone to inaccuracies
Why is the calculation of fetal age from LMP prone to inaccuracies?
- Cycle length can vary
- Implantation bleeding happens at 14 days
What is the advantage of fetal aging using developmental criteria?
Allows accurate estimation of fetal age
What developmental criteria can be used to measure fetal age?
- Crown-rump length
- Bi-parietal diameter
- Abdominal circumference and femur length
- 3- or 4-D USS
When is crown-rump length used to estimate fetal age?
Betwen 7 and 13 weeks
What happens after 13 weeks, regarding using crown-rump length to estimate fetal age?
The relationship is less predicatble
What is the bi-parietal diameter?
The distance between parietal bones of the fetal skull
How is the measurement of bi-parietal diameter used?
In combination with other measurements to date pregnancies in T2 and Y3
Other than fetal aging, what is the use of bi-parietal diameter?
Can see ventricular system of the brain, therefore can look for any malformations
How is abdominal circumference and fermur length used?
- In combination with BPD for dating and growth monitoring
- Anomaly detection
What is the difference between 3D and 4D USS?
4D includes movement
How is 3D and 4D USS used?
As a complimentary tool, not likely to replace standard USS
What abnormality can be seen on 3D and 4D USS?
Can see cleft lip and palate
What birth weight is considered to be average?
What birth weight suggests growth restriction?
What birth weight is considered to be macrosomia?
What is the most common cause of macrosomia?
Poorly controlled maternal diabetes
Are all factors that influence birth weight pathological?
Why may babies have a low birth rate?
- Premature, and they are the normal weight for their gestational age
- Constitutionally small
- Suffered growth restriction
Why may a baby be constitutionally small?
Small mothers tend to have small babies
Why do we want to try and identify babies that have suffered growth restriction during antenatal screening?
Because it is associated with neonatal morbidity and mortality
Why do the lungs develop relatively late?
Beause they have no function during embryonic life
What does embryonic development create, regarding the lungs?
Only the bronchopulmonary tree
What is the respiratory diverticulum made of?
Endoderm tissue that buds off from the primitive gut tube
How is the respiratory diverticulum and the gut tube seperated?
Tracheoesophageal septum is formed to seperate the tracts
When does functional specialisation of the respiratory system occur?
In the fetal period
What are the stages of functional specialisation of the lungs?
- Pseudoglandular stage
- Canalicular stage
- Terminal sac stage
When is the pseudoglandular stage?
What happens in the pseudoglandular stage?
Begin to develop a series of primitive ducts within the broncopulmonary segments created during the embryonic periods, getting down to the formation of bronchioles
When is the canalicular stage?
What happens in the canalicular stage?
Formation of respiratory bronchioles
How are respiratory bronchioles formed in the canalicular stage?
Bud off from the bronchioles formed during the pseudoglandular stage
When is the terminal sac stage?
What happens in the terminal sac stage?
Terminal sacs begin to bud off from the respiratory bronchioles, and differentiation of type I and II pneumocytes
What do type II pneumocytes produce?
What does the terminal sac stage allow?
The respiratory system to function as a gas exchange membrane
What does the fetal development of the lungs have major implications for?
Why does the development of the lungs have major implications for pre-term survival?
Because the baby cannot surviva without a membrane for exchanging gas
Why can't the threshold of viability be continuously pushed back?
Since there is a limit beyond which the lungs will not be sufficiently developed to sustain life
When is a fetus viable?
Only once the lungs have entered the terminal sac stage of development, at 24 weeks
What often affects infants born prematurely?
Respiratory distress syndrome
What causes respiratory distress syndrome?
Insufficient surfactant production due to there not being enough type II pneumocytes
What can be done if a pre-term delivery is unavoidable or inevitable?
Give glucocorticoids treatment to mother
How does giving glucocorticoid treatment to the mother help prevent respiratory distress syndrome?
Pushes fetal type II pneumocytes to produce more surfactants, allowing for mitigation of some of the consequences of pre-term delivery
How is gas exchange conducted during T2 and T3?
At the placenta
When must the lungs be prepared to assume the full burden of gas exchange?
How are the lungs prepared to take the full burden of gas exchange at birth?
What is the importance of breathing movements of the fetus?
Conditions the respiratory musculature- the diaphragm and intercostals
What does the fluid filling the lungs contain?
What is the fluid filling the lungs crucial for?
Normal lung development
What is the fetal cardiovascular system arranged to do?
Ensure that oxygenated blood collected by the umbilical vein at the placenta is circulated around the fetus
When is the definitive fetal heart rate reached?
Around 15 weeks
What is the definitive fetal heart rate?
What is fetal bradycardia associated with?
When does fetal kidney function begin?
In week 10
What is the importance of fetal urine?
It is a major contributor to amniotic fluid volume
Theorectically, what would happen if a fetus had no kidney function?
Fetal kidney function is not necessary for survival in utero, but without it there is oligohydramnios
Why is fetal kidney function not necessary for survival in utero?
Because placenta is doing the renal function
What is oligohydramnios?
Too little amniotic fluid
What could oligohydramnios be due to?
Why can placental insufficiency cause oliohydramnios?
Because very early in pregnancy, placental membranes are responsbile for AF production
Give an example of a condition that would give fetal renal impairment?
Bilateral renal agenesis, which is incomptaible with life
What is polyhydramnios?
Too much amniotic fluid
What can cause polyhydramnios?
- Sometimes idiopathic
- Fetal abnormality, e.g, inability to swallow
How does the timing of nervous system development compare to the other systems?
First to begin development, last to finish
When does fetal movement begin?
What happens, regarding fetal movements, from the 8th week onwards?
A large repertoire of movements development
What is the importance of the development of a large repertoire of movements in fetal life?
Practicing for post-natal life
Give two examples of movements a fetus might perform to practice for post-natal life
When does corticospinal tract development begin to form?
In the 4th month
What are corticospinal tracts required for?
Coordinated voluntary movements
When does myelination of the brain begin?
In the 9th month
What evidence is there for corticospinla tract myelination being incomplete at birth?
Increasing infant mobility in the 1st year, with babies not being able to walk until a year old
What is the implication of development of the fetal nervous tract?
What is quickening?
Maternal awareness of fetal movements
When does maternal awareness of fetal movements begin?
17 weeks onwards, but later in first pregnancy, earlier in later pregnancies
How can quickening be used clinically?
It is a low cost, simple method of ante-partum fetal surveillance
How can quickening be used in fetal surveillance?
Can report changes in pattern of movement, and reveal fetuses requiring follow up