9.2 Fetal Development Flashcards
What are the 3 main periods of pregnancy?
Pre- embryonic (0 to 2 weeks)
Embryonic (3 to 8 weeks)
Fetal (9 to 38 weeks)
What happens during the fetal period of pregnancy?
Growth and physiological maturation of the structures created during the (v much shorter) embryonic period Period involving preparation for the transition to independent life after birth
When is pregnancy calculated from?
From the first day of the last menstrual period.
When is the organogenesis period?
The embryonic period. When the organs are being built and there is intense activity
When do we see significant increase in growth and weight of fetus?
Fetal period
In early pregnancy, what measurement can be used as a marker of fetal growth?
Crown to rump length in the pre-embryonic, embryonic and early fetal periods
Describe fetal growth in the embryonic period
intense morphogenesis & differentiation; little weight gain;
placental growth most significant
How does weight gain vary throughout the fetal period?
Early fetus - protein deposition
Late fetus - adipose deposition ( brown adipose)
How do body proportions change during the fetal period?
At 9 weeks, the head is approximately half the crown-rump length.
Later the trunk and limb growth accelerates.
Even at birth the head represents 1/4 of the length of body
How do we make assesssments of fetal well being?
- Fetal movements - should detect at 15/16 weeks, any changes in fetal movements
- Regular measurements of uterine expansion - symphysis-fundal height
- Ultrasound scan
What are the benefits of using obstetric ultrasound scan?
Safe assessment of growth and development of fetus
Early pregnancy = used to calculate age, rule out ectopic, number of foetuses
When is an obstetric ultrasound scan carried out and why?
Routinely carried out at 20 weeks to assess fetal growth (now big enough for assessment) and fetal anomalies
‘Anomalies scan’
How do we estimate fetal age?
Last menstrual period
Developmental criteria - more accurate
Why is LMP prone to inaccuracy?
Date of conception not always known
Variation of length and duration of menstrual cycle
What is the developmental criteria used to estimate fetal age?
Size against projected normal growth curve
When is crown-rump length used to date the pregnancy?
Between 7 and 13 weeks
What is an ultrasound scan in the first trimester used for?
To measure crown rump length
Check location
Number
Viability (heart beat)
In the second and third trimesters, what measurements are used assess fetal growth an dating?
Biparietal diameter - distance between the parietal bones of the fetal skull
Abdominal circumference
Femur length
- also useful for anomaly detecting, EDD
What key body structures are assessed during an ultrasound in T2/T3?
Neural tube ( brain, spinal cord ) Heart
What is the average brith weight?
3.5 kg
Under what birth weight suggests growth restriction?
2.5kg
Over what weight suggests macrosomia?
4.5kg
What is a key cause of macrosomia?
Poorly controlled maternal diabetes
What is meant by a constitutionally small birth weight?
A non-pathological small birth weight, often due to small maternal size
Why might a babies birth-weight be low?
Premature
Constitutionally small
Suffered growth restriction (associated with neonatal morbidity and mortality)
Why is the development of the respiratory system a key consideration in premature births?
As lungs develop relatively late
What elements of the respiratory system is made during embryonic development?
Creation of Bronchopulmonary tree
What development of the respiratory system is seen during fetal period?
All functional specialisation
Differentiation of the tissues needed to exchange gas
Where does the respiratory tract develop from in the embryonic period?
Respiratory diverticulum branches from the proximal part of the foregut of the primitive gut tube.
Tracheoesophageal septum separates the GI tract and respiratory tract.
Trachea and two main bronchi develop
What is the pseudoglandular stage?
The duct system and bronchioles begin to develop at the start of the fetal period. Occurs in weeks 8 to 16
What is the canalicular stage?
Formation of the respiratory bronchioles budding from bronchioles formed in the pseudoglandular stage
Occurs in weeks 16 to 26
What is the terminal sac stage?
The terminal sacs begin to bud from the respiratory bronchioles
Differentiation of type I and type II penumocytes which reduce surfactant
Occurs from week 26 to term in trimester 3
How do lungs prepare for birth?
Breathing movements - conditioning of the respiratory musculature, diaphragm so that the respiratory muscles develop and don’t atrophy
Fluid filled - lung fill with amniotic fluid. Helps lung development as exposes to mediators that promote growth
What determines the viability for pre-term survival?
The development of the lungs.
Viability is only a possibility once the lungs have entered the terminal sac stage of development ( after 24 weeks)
What is respiratory distress syndrome?
Insufficient surfactant production, cant maintain reduction in surface tension in the lungs and gas exchange compromised
Who is most affected by respiratory distress syndrome?
Pre-mature infants
If pre-term delivery is unavoidable or inevitable (e.g. in pre-eclampsia) , what treatment should be given?
Glucocorticoid treatment to the mother
- increases surfactant production in the fetus
When is definitive fetal H/R achieved?
Around 15 weeks
What clinical sign can be associated with fetal demise?
Fetal bradycardia
When does fetal kidney function begin?
Week 10
What is oligohydramnios?
Too little amniotic fluid
What causes oligohydramnios?
Placental insufficiency
Fetal renal impairment
(Less urine and placental secretion)
What causes Polyhydramnios?
Fetal abnormality ( inability to swallow - defects in GI tract/ blind ended oesophagus/ neurological problem)
What is polyhydramnios?
Too much amniotic fluid
What are corticospinal tracts required for?
For development of the nervous system to allow coordinated voluntary movements
When do the corticospinal tracts develop?
In the 4th month
When does myelination of the brain begin?
In the 9th month
Why does infant mobility increase in the 1st year?
As myelination of the nervous system not complete at birth
When does movement of the fetus begin?
After the 8th week with the startle movement
When are fetal movements detected by the mother?
From 17 weeks onwards
What is fetal ‘quickening’?
Fetal movements detected by the mother
Useful ante-partum fetal surveillance
When does the cerebellum begin development?
Week 16
When does myelination begin in the brain?
Week 36
What produces surfactant?
Type 2 pneumocytes
What is the first body system to develop?
Nervous system
What is the last body system to finish development?
Nervous system
