Embryology in USS Flashcards
What is the Foetal Anomaly Screening Programme? (FASP)
It sets guidelines and standards for foetal screening and anomaly detection
This ensures high standards of screening and national consistency
When are the pregnancy points of screening?
- first trimester
(10-14 weeks)
- second trimester
(18 - 20/26 weeks)
When is screening undertaken in the first trimester?
What is this?
At 10 - 14 weeks
This is known as a dating USS (ultrasound scan)
What is the purpose of a Dating USS?
- estimating current gestational age
2. calculating the due date (40 weeks)
What tests are also undertaken on women who opt for screening?
- maternal blood sample
2. nuchal translucency
What is the abnormalities are tested for at 10-14 weeks?
Testing for:
- T21 - Down’s syndrome
- T18 - Edwards’ syndrome
- T13 - Patau’s syndrome
What is involved in the combined screening test in the first trimester?
- Papp-A
- HcG
- Nuchal translucency
What is involved in the quad test during first trimester screening?
- AFP
- HCG
- uE3
- Inhibin A
What is measured in nuchal translucency (NT)?
What is normal?
The thickness of the skin at the back of the neck
Normal is < 3.5 mm
What may an abnormal NT scan be due to?
It may be excessively oedematous
This is due to blockage of fluid in the developing foetal lymphatic system
Why is nuchal translucency only significant if measured between 10 and 14 weeks of gestation?
The foetal lymphatic system is developing and the peripheral resistance of the placenta is high
After 14 weeks, the lymphatic system is developed and will drain away excess fluid
What is the problem with using a nuchal translucency scan after 14 weeks?
Any abnormalities causing fluid accumulation may seem to correct
They can go undetected by nuchal screening
What causes Down’s syndrome?
Non-disjunction (92%) or translocation (4%)
It affects 1 in 800 births
What is the ethical dilemma involved in deciding whether to terminate a trisomy 21 pregnancy?
The severity of the physical and intellectual disability is difficult to predict
How does the intellectual disability in trisomy 21 usually present?
Mild to severe
Social skills are usually good
What % of Down’s syndrome babies are affected by congenital heart disease and AVSD/VSD?
congenital heart disease - 40%
AVSD/VSD - 80%
What are the typical physical characteristics of a baby with Down’s syndrome?
- small chin
- slanted eyes
- flat nasal bridge
- single palmer crease
- large tongue
- shorter stature
- sleep apnoea
What % of Down’s syndrome children have visual and hearing problems?
80% have visual problems - including cataracts
90% have hearing problems - otitis media
How independent are children with Down’s syndrome?
They can live semi-independent lives and attend mainstream schools
What is trisomy 18?
What causes it?
Edwards syndrome
It is caused by non-disjunction and affects 1 in 3-5000 births
What is the median lifespan for someone with Edwards syndrome?
5 - 15 days
60% will die in utero
What are the physical abnormalities of someone with Edwards syndrome?
- small stature
- microcephaly
- cleft lip
- low set ears and small jaw
- clenched hand/fist
What is trisomy 13 and what causes it?
Patau syndrome
It is caused by non-disjunction or translocation
it affects 1 in 5-10,000 births
What is the median lifespan for someone with Patau syndrome?
Median lifespan is 5 - 15 days
60% will die in utero
What are the physical abnormalities of someone with Patau syndrome?
- severe mental disability
- small stature
- seizures
- facial clefts
How is the foetal head formed?
From the neural crest and mesoderm
Followed by intramembranous ossification
What is anencephaly and what is it caused by?
Failure of fetal skull formation leads to the exposure of brain contents to pressure effects
What is the mortality and detection rate of anencephaly?
100% mortality rate
98% detection rate in first trimester
When does the gastrointestinal tract develop?
It derives from endoderm during week 3
What are the 3 parts of the gastrointestinal tract?
- foregut goes from oesophagus to upper part of duodenum
- midgut runs to 2/3 along the transverse colon
- hindgut runs to the rectum
What happens to the midgut during the 6th week of development?
It herniates through the umbilical cord
It undergoes 270o rotation anticlockwise
This is completed by the 12th week
What characterises an abnormal herniation?
If herniation remains after 12 weeks
What is gastroschisis and how many births does it affect?
Herniation of the intestinal contents
This is most commonly the bowel, but may include liver and stomach
Affects 4 in 1000 births
How is gastroschisis corrected?
Surgery after birth
How many births are affected by omphalocele?
1 in 4000
How does omphalocele differ to gastroschisis?
- associated with higher rates of genetic defects
- involves the umbilical cord
- poorer outcome
What types of screening happen in the second trimester?
Anatomy/anomaly USS
This occurs between the 18th and the 20th-26th week
What type of USS is included in second trimester screening?
What specific conditions are tested for?
Detailed examination of the heart and brain
Looking for:
- spina bifida
- cleft
- cardiac defects
What is significant about the developmental period of the nervous system?
it is one of the earliest systems to develop (week 3) and last to complete
The long period of development means it is susceptible to insult
What is the incidence of spina bifida?
1 in 500 to 1 in 2000
What causes spina bifida?
A failure of the vertebral arches to close
This is most commonly lumbar (75%) and sacral (15%)
What can prevent spina bifida?
- folic acid supplementation
What drug is known to increase risk of spina bifida?
Sodium valproate (1%)
This is a drug used to treat epilepsy
What are the physical impairments that are present due to spina bifida?
The level of physical impairment depends upon the location of defect
- leg weakness
- bladder or bowel incontinence
- sexual dysfunction
What is the risk associated with spina bifida?
Risk of developmental delay
What causes a cleft lip?
What is the incidence?
Failure of fusion by 12 weeks
Incidence is 1 in 1000
What are midline clefts associated with?
Higher rates of genetic conditions
