Fetal development

Question 1

When are the pre-embryonic, embryonic and fetal periods

Answer 1

pre-embryonic: 1-2 weeks
embryonic: 3-8/9 weeks
fetal-9 to 38 weeks ish

Question 2

How are pregnancy weeks calculated

Answer 2

clinical period is dated from the first day of last the menustrual period

normal is 36 weeks term
40 weeks from point of conception

Question 3

How does the respiritory system develop

Answer 3

-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,

Question 4

How do lungd develop in embroynic and fetal period

Answer 4

-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

Question 5

What happens to the lungs during the second and third trimester

Answer 5

-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

Question 6

What is respiitory distress syndrome

what can you do to help

Answer 6

-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

Question 7

What is a birth defect

Answer 7

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

Question 8

What are teratogens

give examples

Answer 8

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

Question 9

How would we classify the timing

Answer 9

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

Question 10

Definitons

Deformation

Answer 10

ate changes in previously normal structures (mechanical effect)

talipes

Question 11

Defintions

Disruption

Answer 11

secondary disturbance due to early influence of external factors

amniotic bands

Question 12

defintions

sequence

Answer 12

primary defect leads to a cascade of further anomalies

Potter sequence

Question 13

defintions

Malformation

Answer 13

primary disturbance of embryogenesis

Question 14

how do we screen

Answer 14

blood tests, ultrasound scanning

they are non invasive -> not defintive its a chance

Question 15

Diagnositic test

what is it examples

Answer 15

they are invasive
defintive
tests :Amniocentesis / chorionic villus sampling (CVS)

risk: loss of pregenacy benefit: definitve result

Question 16

What is meant by a combined test

Answer 16

• 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)

Question 18

What happens in the quadruple test

Answer 18

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

Question 19

if there is a high chance of t13,18,21 what happends

Answer 19

offered NiPT
then may be offered diagnostic test (invasive)
-e.g Amniocentesis / chorionic villus sampling (CVS)

Question 20

What is Non invasive prenatal test (NIPT)

Answer 20

-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

Question 21

What is the genetic basis of birth defects

Answer 21

Single gene (have point mutations)
Mutation
Deletion

Chromosomes
Translocation
Duplications
Microdeletions

Question 22

How can trisomy 21 happen

Answer 22

-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

Question 23

What is the genetic cause of Di george syndrome

Answer 23

-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

Question 24

What the genetic basis of CHARGE syndrome

Answer 24

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

Question 25

What happens at the 20 week scan

Answer 25

-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

Question 26

What is spina bifida and anencephaloy

Answer 26

failure to close anterior or posteior neural tube can cause defects

Caudal NT defect results in spina bifida
Cranial NT defect results in anencephaly

Question 27

Spina bifida

Answer 27

-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

Question 28

Cleft lip and palate

Answer 28

if isolated can cause
-Difficulty feeding
* Hearing problems
* Dental problems
* Speech problem

can be surgically corrected

this can be assoicated with trisomy 13, 18

Question 29

How does the nose and upper lip development

Answer 29

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

Question 30

How does palate devleopment

Answer 30

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

Question 31

Gastroschisis

Answer 31

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,

Question 32

Omphalocoele

Answer 32

-herniation of midgut
-associated with chromosomal abnormalities

20% chromosomal abnormalities e.g.
Edwards T18

Question 33

Congential heart defects

Answer 33

-most common birth defects
-associated with chromosomal abnormalities
-90% survive until adulthood

defects can occur in chambers, can occur in aorta, great arteries

Question 34

Prevention of defects

Answer 34

▪ 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