Repro 9.2 Foetal Growth and Development Flashcards
When does the foetal period begin and end?
Begins at the 8th week post conception and ends at birth
In general terms what happens during the foetal period?
Growth and maturation of systems laid down during the embryonic period to fit the individual for birth and postnatal life
What are the most important body systems for determining survival outside the uterus?
Nervous
Respiratory
CVS
Urinary
What is the embryonic period also known as?
Organogenetic period - intense morphogenesis and differentiation. Includes little weight gain. Absolute growth is very small except the placenta
What causes major weight gain during the foetal period?
Early foetal period - protein deposition
Late foetal period - adipose deposition
What are the potential reasons for a small neonate?
Premature birth
Intra-uterine growth retardation
Constitutionally small
What 3 broad categories may age of foetus be estimated by?
Duration of pregnancy
Developmental criteria
Syphysis - fundal height
How is the duration of pregnancy assessed?
Fertilisation age
Age since mothers last menstrual period (+2 weeks of fertilisation age)
Why is the duration of pregnancy prone to inaccuracy?
Irregular menstrual cycles
Mother may not be confident of last menstrual period date
How can the developmental criteria be assessed?
Ultrasound
What is measured during ultrasound to assess development?
Crown-rump length Foot length Biparietal diameter of head Abdominal circumference Femur length
How can age be assessed after delivery?
Weight and appearance
Why and when is crown-rump length measured?
7 - 13 weeks to date pregnancy and estimate EDD. Crown rump length increases rapidly in pre-embryonic, embryonic and early foetal periods so will give a good indication of age
What is biparietal diameter of the head?
Distance between parietal bones of the foetal skill (assessed in T2 and 3)
What are abdominal circumference and femur length used for?
Used with BPD for dating and growth monitoring
Also useful for anomaly detection
What is symphysis-fundal height?
Distance from the symphysis pubis to top of uterus
How is the symphysis-fundal height measured?
Can be measured with a tape measure and should relate to weeks (e.g. 20 weeks, 20cm although plateaus after 36 weeks)
Height of fundus can also be measured in relation to other structures e.g. umbilicus, xiphisternum
Where is the uterus palpable at week 12?
Above the pelvis
How is intrauterine/foetal growth restriction assessed?
A lag of 4cm or more of the fundal height
What sources can cause variability in estimation of foetal age?
Number of foetuses
Volume of amniotic fluid
Extent of engagement of the head
Postion of the foetus
What are the advantages of ultrasound?
Safe
Can be used in pregnancy to calculate age also location, number and viability
What is the purpose of the 20 week scan?
Assess foetal growth and anomalies
What is considered to be low, normal and high birth weight?
Low 4500g = macrosomia
What are the 4 phases of maturation of the lungs?
Pseudoglandular (8-16wks) Canalicular (16-26 wks) Terminal Sac (26 - term) Alveolar period (late foetal to 8 years)
What development of the respiratory tract occurs in the embryonic period?
Bronchopulmonary tree forms
Respiratory diverticulum is separated from the oesophagus by the tracheoesophageal septum
What histological changes occur in the respiratory system in the pseudoglandular phase?
Duct system forms
Airways formed as far as terminal branches
What histological changes occur in the respiratory system in the canalicular phase?
Building from bronchioles, some terminal sacs begin to form at 24 wks
More vascular
What histological changes occur in the respiratory system in the terminal sac phase?
Many primitive sacs form and some primitive alveoli
Differentiation of pneumocytes to type I and II
Surfactant formed from week 20
What histological changes occur in the respiratory system in the alveolar period?
Alveoli form (95% post-natally)
When does a pregnancy become viable?
Once lungs have entered the terminal sac stage of development (>24 weeks)
When and why does the foetus begin breathing movements?
12-14 weeks to condition respiratory musculature and enable aspiration of amniotic fluid
Why are the foetal lungs filled with fluid and where is it from?
Essential for normal lung development
Aspirated amniotic fluid and secreted fluid
When is aspirated amniotic fluid removed?
Expelled during vaginal birth and any remaining is absorbed
What causes pulmonary resistance to fall at birth?
Opening of the alveoli at the first breath
What causes respiratory distress syndrome?
Insufficient surfactant often in premature babies
How is the pregnancy treated if preterm delivery is unavoidable or inevitable?
Treat mother with corticosteroids to increase surfactant production in foetus
What is the fastest developing organ in the foetus and infant?
Brain
What % of the foetus body weight does the brain account for at birth?
12%
What changes occur in the brain in the foetal period of development?
Cerebral hemisphere becomes the largest part of the brain
Histological differentiation of cortex in the cerebrum and cerebellum
Formation and myelination of nuclei and tracts
Relative growth of the spinal cord and vertebral column
When do the gyri and sulci form?
After 5 months as the brain grows faster than the head
What are the corticospinal tracts required for and when do they form?
Required for voluntary movements
Begin to form in the 4th month
When does myelination of the brain begin?
9th month - continues after birth e.g. myelination of the corticospinal tracts is incomplete and evidently continues after birth as infants mobility significantly increases in the first year
Which senses mature first?
Hearing and taste before vision - the corti of the inner ear is well developed at 5 month but the retina is immature at birth
little evidence exists for smell
At what stage of development is the foetus able to feel pain?
Histological studies suggest that ascending tracts are present though not myelinated as early as 19 weeks. This has implications on the possibility of intra-uterine surgery on the foetus and invasive procedures of the premature
When do foetal movements being?
Seen on ultrasound at 8 weeks but not felt by mother until around 17 weeks
Large repetitive movements develop, ‘practicing’ for post-natal life
What aspects of brain development are of clinical importance?
Foetal movements
Viability (sufficiently mature to control body functions?)
Sensory awareness
Maternal/neonatal nutrition and cortical development
What is the functional foetal kidney?
The metanephros
When is kidney ascent complete and when does function begin?
10 weeks
How do children’s kidneys differ to cult kidneys and at what age does this change?
lobulated until 4-5 years of age
When do glomeruli and tubules of the kidneys develop?
Present at 10 weeks
When do pelvis and calyces etc of the kidneys develop?
By 23 weeks
When is histological differentiation of the cortex and medulla of the kidneys complete?
8 months
Where does the bladder lie in the foetus and infant?
Abdominal cavity
What happens to urine in the bladder of a foetus?
Enters the bladder and is emptied into the amniotic fluid to be swallowed by the foetus
How regularly does the bladder of a foetus fill and empty and how is this of benefit?
Every 40-60 minutes
Used clinically to assess foetal urinary function
What does polyhydramnios indicate?
Foetal abnormality eg inability to swallow
What does oligohydramnios indicate?
Kidney function impairment
Placental insufficiency
What is the function of the foetal circulation?
Adapted to bring oxygenated blood from the placenta to the foetus via umbilical vessels
When is definitive heart rate achieved in the foetus?
Around 15 weeks
What does foetal bradycardia indicate?
Foetal demise
