Foetal growth and development Flashcards
What is the foetal period?
- From 9 weeks gestation
- Growth and physiological maturation of structures created during embryonic period
- Involves preparation for transition to independent life after birth
Compare patterns of growth in the embryonic period versus the foetal period
- Embryonic period is characterised by intense activity but absolute growth is very small (except placental)
- Placental growth most significant in embryonic period
- Growth and weight gain accelerate in foetal period
Outline stage one of normal intrauterine growth
- Hyperplasia
- 4-20 weeks
- Rapid mitosis
- Increasing DNA content
- Symmetric
Outline stage 2 of normal intrauterine growth
- Hyperplasia/hypertrophy
- 20-28 weeks
- Declining mitosis
- Increasing cell size
-Mixed - asymmetric
Outline stage 3 of normal intrauterine growth
- Hypertrophy
- 28-40 weeks
- Rapid hypertrophy
- Rapid increasing cell size
- Rapid accumulation of fat, muscle, connective tissue
- Asymmetric
Outline differential growth throughout the different periods of pregnancy
- Crown rump length increases rapidly in pre-embryonic, embryonic and early foetal periods
- Weight gain is slow at first, then increases rapidly in mid and late foetal periods
What is the difference between deposition in the early foetus and the late foetus?
- Early foetus - protein deposition
- Late foetus - adipose deposition
How do body proportions change during the foetal period?
- At 9 weeks the head is approximately half crown-rump length
- Thereafter, body length and lower limb growth accelerates
How is foetal wellbeing assessed before birth?
- Foetal movements (start at 8 weeks and can be felt by mother at 20 weeks)
- Regular measurements of uterine expansion
- Ultrasound scans
How do we measure uterine expansion?
- Symphysis-fundal height
- Measured from top of uterus to pubic bone
- Normally = number of weeks +/- 2cm
What are the different obstetric ultrasound scans?
- 12 week scan
- 20 week scan
- Additional scans for growth measurement/ to assess foetal wellbeing
What is checked for at 12 week scans?
- Determines gestational age
- Detects multiple pregnancies
- Screening for chromosomal abnormalities if opted for
- Nuchal translucency scan
What is checked for at 20 week scans?
- Screen for foetal abnormalities (heart, kidney, spine)
- Determine placental location (e.g. placenta praevia)
How do we estimate foetal age?
- Last menstrual period (prone to inaccuracy)
- Developmental criteria allow accurate estimation of foetal age
How is crown-rump length measured?
- Measured between 7&13 weeks to date pregnancy and estimate EDD
- Scan in T1 also used to check location, number, viability
- Very accurate
What is the biparietal diameter?
- Distance between parietal bones of foetal skull
- Used in combination with other measurements to date pregnancies in T2 and T3
What is abdominal circumference and femur length?
- Used in combination with biparietal diameter
- Dating, growth monitoring, anomaly detection
What is the average normal birth weight?
- 3.5 kg
How is low birth weight classified?
- Less than 2.5 kg
- Very low birth weight is between 1.0-1.5kg
- Extremely low birth weight is up to 1.0 kg
How is macrosomia defined?
- > 4kg
Why can babies have low birth-weight?
- Premature
- Constitutionally small
- Have suffered growth restriction - associated with neonatal morbidity and mortality
Outline symmetrical intrauterine growth restriction
- Head circumference, abdominal circumference, biparietal diameter and foetal length are all proportionally reduced
What causes symmetrical intrauterine growth restriction?
- Genetic disorders
- TORCH infections
Outline asymmetrical intrauterine growth restriction
- Abdominal circumference decreased
- Biparietal diameter, head circumference and femur length are all normal
- Brain sparing
- Result of placental insufficiency (e.g. in pre-eclampsia)
Give an overview of the development of the respiratory system?
- Lungs develop relatively late
- Embryonic development creates bronchopulmonary tree only
- Major implications for pre-term survival
Outline how the respiratory system develops between weeks 8-16
- Duct system begins to form within bronchopulmonary segments created during embryonic period
- These become bronchioles
- Around 8 weeks foetus starts moving fluid out of lungs
Outline how the respiratory system develops between 16-26 weeks
- Formation of respiratory bronchioles
- Budding from bronchioles formed during pseudoglandular stage
Outline how the respiratory system develops at 26 weeks
- Terminal sacs begin to bud from respiratory bronchioles
- Cuboidal cells start differentiating to type I and type II pneumocytes
- Pneumocytes produce surfactant needed for gas exchange
- Gas exchange possible towards end of this stage (from 24 weeks onwards)
- Tissue thins to assist gas exchange
What happens to the lungs during T2 and T3?
- Gas exchange is conducted at placenta, but lungs must be prepared to assume full burden at birth
- ‘Breathing’ movements
- Conditioning of respiratory musculature
- Fluid filled - crucial for normal lung development
How can we prevent premature birth?
- Mum can be given steroids to help baby produce surfactant
When is foetal viability possible?
- Once lungs have entered terminal sac stage of development
- > 24 weeks
What is respiratory distress syndrome?
- Often occurs in infants born prematurely
- Insufficient surfactant production
- If pre-term delivery is unavoidable or inevitable
- Mother is treated with glucocorticoids
- This increases surfactant production in foetus
Outline the development of the foetal cardiovascular system
- Foetal cardiovascular system ensures that oxygenated blood collected by umbilical vein at placenta is circulated around foetus
- Definitive foetal H/R is achieved at around 15 weeks
- Foetal bradycardia associated with foetal demise
Outline the development of the foetal urinary system
- Kidney function begins in week 10
- Foetal urine is a major contributor to amniotic volume from 20 weeks onwards
- Foetal kidney function is not necessary for survival in utero
- Without it there is oligohydramnios
What is oligohydramnios?
- Too little amniotic fluid
- Placental insufficiency
- Foetal renal impairment
- Premature rupture of membranes
- Pre-eclampsia
What is polyhydramnios?
- Too much amniotic fluid
- Foetal abnormality (e.g. oesophageal atresia/anencephaly)
- Gestational diabetes
- Foetal anaemia
- Multiple pregnancy
Outline the development of the foetal nervous system
- First system to begin development and last to finish
- Corticospinal tracts required for coordinated voluntary movements begin to form in 4th month
- Myelination of brain only begins in 9th month
- Corticospinal tract myelination is incomplete at birth - this is why infant mobility increases during 1st year of life
Outline the development of foetal sensory and motor systems
- No movement until 8th week
- Thereafter a large repertoire of movements develop
- Allows foetus to practise for post-natal life
- E.g. suckling, breathing
- Maternal awareness of foetal movements from 15-17 weeks onwards
Give a timeline of foetal lung development
- 9 weeks - lungs begin functional adaptation
- 24 weeks - terminal air sacs appear, some surfactant production
- 36 weeks - greatly increased surfactant production
Give a timeline of foetal brain development
- 16 weeks - cerebellar development, corticospinal tracts begin to form
- 20 weeks - myelination begins in spinal cord
- 28 weeks - characteristic gyri and sulci appear as cerebellar hemispheres grow larger than skull
- 36 weeks - myelination begins in brain
