Fetal development Flashcards
When are the pre-embryonic, embryonic and fetal periods
pre-embryonic: 1-2 weeks
embryonic: 3-8/9 weeks
fetal-9 to 38 weeks ish
How are pregnancy weeks calculated
clinical period is dated from the first day of last the menustrual period
normal is 36 weeks term
40 weeks from point of conception
How does the respiritory system develop
-lungs develop late
-in embryonic period only the bronchopulmonary tree is created (so you have trachea and main bronchi)
-in the fetal period we start to make air sacs, and smaller airways, we do functional specialsation
because of late developmental stage of lungs is late,
How do lungd develop in embroynic and fetal period
-lungs occur as divericulumn of gut tube (endoderm)
-seperate gut from respirtory system
-so we form a tracheo-oesophageal septum
-they then seperate
past embryonic period
-16th week: we have bronchioles
-around 26 weeks we have respiyory bronchioles
around 30 ish -start to make alveoli, get type 1 cells (squamous epitheilium for gas exchnage)
type 2 cells make surfctant -> reduces surface tension in lungs
tracheo-oesophageal septum -> defects can have fistula between two
What happens to the lungs during the second and third trimester
-fetus is practising breathing
-start to condition respitory muscles
-this allows lungs to inhale amniotic fluid, which help development of type 1 and 2 cells etc
What is respiitory distress syndrome
what can you do to help
-occurs with premature babies
-have insuffcient surfcanat production
if you have to deliver baby, is inevitbale
-can treat mother with glucocorticoids, -> cortisol needed to make surfactant which quickens the surfactant making process
What is a birth defect
definition: present at birth, due to problems with development of sturtcure or systems
-it can be a structual problem
-can be functional and metabolic
-there are a wide range causes (single gene defects, chromosomal, polygenic, teratogenic, or unknown)
35-40% is an unknown cause
What are teratogens
give examples
an agent that can intefer with normal development agent
examples
-Congenital infection (TORCH, rubella, Zika virus, CMV)
▪ Drugs and Environmental pollutants / insecticides (Vit A, pesticides, medications, alcohol)
▪ Maternal metabolic disease (undermanaged DM)
▪ Radiation exposure (ionising radiation is a mutagen)
it depends on where you live in the world
How would we classify the timing
Pre-embryonic (pre wk 2)
if there is a teratogen there is a all or nothing effect is either
Lethal or no has effect
▪ Early effects (2-4 wks) Scattered pattern
▪ Later effects (4-8 wks) Localised defect
▪ Fetal period (>9 wks)
Organ growth and functional maturation affected
Cns can be affected trhoighout whole pregnancy
Definitons
Deformation
ate changes in previously normal structures (mechanical effect)
talipes
Defintions
Disruption
secondary disturbance due to early influence of external factors
amniotic bands
defintions
sequence
primary defect leads to a cascade of further anomalies
Potter sequence
defintions
Malformation
primary disturbance of embryogenesis
how do we screen
blood tests, ultrasound scanning
they are non invasive -> not defintive its a chance
Diagnositic test
what is it examples
they are invasive
defintive
tests :Amniocentesis / chorionic villus sampling (CVS)
risk: loss of pregenacy benefit: definitve result
What is meant by a combined test
- Needs to be done before 14 weeks (early test)
-can be barriers seeking and accessing antenatal care - Covers paramaters like Maternal age (biggest risk factor for chromosomal abnormailties) + nuchal translucency (meausre thickness of nuchal fold in ultrasound)
+ do a serum free bhCG and PAPP-A
results are added together
Reports chance of Trisomy21 (down syndrome) and Trisomy18/Trisomy13 (pateu, edwards)
What happens in the quadruple test
when its hard to measure nuchal ligament, or there was an inablity to access anetal care before 14 weeks this test is done
measures
maternal age, bhCG, unconjugated E3, Inhibin A and AFP
* Tests for Trisomy 21 only
if there is a high chance of t13,18,21 what happends
offered NiPT
then may be offered diagnostic test (invasive)
-e.g Amniocentesis / chorionic villus sampling (CVS)
What is Non invasive prenatal test (NIPT)
-allows for fetal DNA to be extracted from maternal lasma
-use DNA technology to amplify sequences, map to genome
-look for chromsomes
-then calculate how many copies of chromsomes there are
-to statical analysis
What is the genetic basis of birth defects
Single gene (have point mutations)
Mutation
Deletion
Chromosomes
Translocation
Duplications
Microdeletions
How can trisomy 21 happen
-can have non dysjunction (94%)
-one daughter cell got both chromsome and the other got none
-and then in fertilisation get one more from partner -> trisomy of 21
Robertsion translocation
-one parent is a carrier (chromsome 21 is stuck on chromsome 14)
-then if carried onto gamete
What is the genetic cause of Di george syndrome
-due to deletion of a section of chromosome 22
-TBX1 is removed (usually co-rodinates the events in making the crainofacial, pahrengyl reigon)
-causes ananmolies of craniofacial and pharengyl reigon
- failure of development 3rd and 4th pharengyl pouch
What the genetic basis of CHARGE syndrome
CHD7 (chromodomain helicase DNA-
binding domain, ATP-dependant chromatin emodeller) -> has been mutated
* mutation causes CHARGE syndrome (coloboma, heart defects, chonal atresia, growth and devleopment impairment, genetial hypoplasia, ear defects)
- CHD7 heterozygous mutation
- CHD7 expression essential for the
production of multipotent neural crest cells
What happens at the 20 week scan
-screen for 11 conditions
-assess craniofacial development, femur, spine, abdominal circumferance plus cardiac development
NHS assessing
anencephaly
open spina bifida
cleft lip
diaphragmatic hernia
gastroschisis
exomphalos
serious cardiac abnormalities
bilateral renal agenesis
lethal skeletal dysplasia
Edwards’ syndrome, or T18
Patau’s syndrome, or T13
What is spina bifida and anencephaloy
failure to close anterior or posteior neural tube can cause defects
Caudal NT defect results in spina bifida
Cranial NT defect results in anencephaly
Spina bifida
-spina bifida can occur anywhere along the length of the tube, typically lumboscaral reigon
-hydrocephalus usually occurs
classiffied
-mengingocoele
-> spinal cord protected from veterbrae, mengines and cyst filled with CSF is proturding out
myelomeningcoele
-> neural tube+ mengines is in the cyst, which can be damaged
cause
-multifactorial
-Genetic, environmental, maternal
nutritional status
* Folic acid supplementation
prevents NTDs
Cleft lip and palate
if isolated can cause
-Difficulty feeding
* Hearing problems
* Dental problems
* Speech problem
can be surgically corrected
this can be assoicated with trisomy 13, 18
How does the nose and upper lip development
merging and fusion of different structures
-maxillary prominences grow medially, pushing the nasal prominences closer together in the midline
-then maxillary prominences fuse with medial nasal prominences
* finally medial nasal prominences then fuse in the midline
How does palate devleopment
oral and nasal cavity need to seperated
-we need nasal septum, palatal shelf
-palatal shelves need to grow towards each other and fuse in the midline
Gastroschisis
is when anterior body wall closure defect, lateral to umbilicus
-bowel loops outside body, risk of necrosis
incidence is increasing and is associated in younger mothers
correlation between smoking, recreatioanl drugs,
Omphalocoele
-herniation of midgut
-associated with chromosomal abnormalities
20% chromosomal abnormalities e.g.
Edwards T18
Congential heart defects
-most common birth defects
-associated with chromosomal abnormalities
-90% survive until adulthood
defects can occur in chambers, can occur in aorta, great arteries
Prevention of defects
▪ Good diet and nutrition
Folic acid / iodine supplementation
▪ Avoidance of teratogenic drugs / substances / agents
▪ Vaccination (Rubella)
▪ Screening for infections e.g. Syphilis
▪ Maternal age – increased age a significant risk factor
