Embryological Basis of Disease Flashcards
When is the 1st trimester?
From week 1 to the end of week 12
What does a first trimester screening consist of?
- USS
2. Maternal biochemistry (blood test)
What does a second trimester screening consist of?
- USS (much more detailed)
2. Maternal biochemistry (blood test) if needed
What information does first trimester USS provide?
- Current gestational age
- Due date
What is CRL?
Crown-rump length (CRL) is the measurement of the length of human embryos and foetuses from the top of the head (crown) to the bottom of the buttocks (rump).
Can be used to estimate gestational age.
What info does maternal blood test provide in first trimester?
T21 (Down’s), T18 (Edward’s), T13 (Patau’s)
What is trisomy 18 Edward’s syndrome?
A baby with Edwards’ syndrome has 3 copies of chromosome number 18 instead of 2. This affects the way the baby grows and develops.
Very low chance of survival (5-15 days).
What is trisomy 13 Patau’s syndrome?
3 copies of chromosome 13, instead of 2.
This severely disrupts normal development and, in many cases, results in miscarriage, stillbirth or the baby dying shortly after birth.
Babies with Patau’s syndrome grow slowly in the womb and have a low birth weight, along with a number of other serious medical problems (cardiac defects)
What does the combined screening test in the first trimester consist of?
- Papp-A
- hCG
- NT
What is NT?
Nuchal Translucency
Thickness of the skin at the back of the neck is measured.
Normal < 3.5mm
What is implied if NT is thick?
As nuchal translucency size increases, the chances of a chromosomal abnormality and mortality increase.
When is NT only significant?
Between 10 and 14 weeks of gestation
What can abnormal NT indicate?
May be excessively oedematous. Blockage of fluid in the developing foetal lymphatic system.
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 the excess fluid and after this time any abnormalities causing fluid accumulation may seem to correct and can go undetected by nuchal screening.
What is the quad test?
A maternal blood screening test that looks for four specific substances: AFP , hCG , uE3, and Inhibin-A
What is AFP?
It is a protein made in the liver of a developing baby
What is purpose of AFP test?
The results of your AFP blood test can alert your doctor to possible birth defects. A high level of AFP can be an indication of a neural tube defect such as spina bifida.
What is uE3?
Oestriol (uE3) , a form of oestrogen that increases during pregnancy. It is produced in large amounts by the placenta.
What is purpose of uE3?
Decreased second trimester uE3 has been shown to be a marker for Down and trisomy-18 syndromes
What is inhibin A screened for?
Inhibin A is made by the placenta during pregnancy
The inhibin A test is done to measure the amount of this hormone in a pregnant woman’s blood to see if the baby may have Down syndrome.
What is papp-A?
Pregnancy Associated Plasma Protein A (PAPP-A) is produced by the placenta (afterbirth).
Low levels of PAPP-A may be associated with the placenta not working as well as it should do. This can lead to some babies not meeting their growth potential (not growing as expected).
Low levels of PAPP-A can also be associated with Down’s Syndrome.
What is Down Syndrome caused by?
- Non-disjunction (92%)
- Translocation (4%)
How can non-disjunction cause down syndrome?
Failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division.
Results in an embryo with three copies of chromosome 21.
How many pregnancies affected by trisomy 21 are terminated?
92%
How can translocation cause down syndrome?
Translocation is a type of chromosomal abnormality in which a chromosome breaks and a portion of it reattaches to a different chromosome.
What are the characteristics of trisomy 21?
- Physical disability
- Intellectual disability
- Congenital heart disease (40%)
- AVSD / VSD (80%)
- Physical characteristics
- Visual problems (80%)
- Hearing problems (90%)
What is trisomy 18 most commonly caused by?
Non-disjunction
What is intramembranous ossification?
Process of bone development from fibrous membranes. It is involved in the formation of the flat bones of the skull, the mandible, and the clavicles. Ossification begins as mesenchymal cells form a template of the future bone.
What is anencephaly?
Failure of foetal skull formation, leading to absence of a major portion of the brain, skull, and scalp that occurs during embryonic development.
What is anencephaly caused by?
Neural tube defect that occurs when cranial end of the neural tube fails to close
What are effects of anencephaly?
Exposure of brain contents to pressure effects as brain forms normally
100% mortality
98% rate detection in 1st trimester
How does midgut rotate during development?
During 6th week midgut protrudes through umbilical cord
- Physiological herniation (can be seen in scan)
- 270 rotation anticlockwise.
- This process completes by 12th week.
What is abnormal herniation?
If herniation remains after 12 weeks
What is gastroschisis? What is it an example of?
Abnormal herniation
- Herniation of intestinal contents, mainly bowel (may include liver and stomach)
- This develops outside the baby’s body in the amniotic fluid
What is omphalocele? What is it an example of?
Abnormal herniation
- Associated with higher rates of genetic defects
- Umbilical cord involvement
The intestines, liver and occasionally other organs remain outside of the body wall surrounded by membrane.
What is screened for in 2nd trimester?
Structural defects and specific conditions (anatomy scan)
- Spina bifida
- Cleft
- Cardiac defects
What is most susceptible to defects during development? Why?
Nervous system
One of earliest systems to develop and last to complete (long period of development_
What does the early nervous system develop from?
Neural plate
Folding to become neural tube
What is spina bifida?
Neural tube defect –> failure of vertebral arches to close resulting in gap in spine
What are most common places for spina bifida to occur?
Lumbar (75%) and sacral (15%)
How can spina bifida help to be avoided?
Folic acid supplements
What can be seen in spina bifida scan?
Bulge on spine –> may contain only fluid or nerves as well
What does the level of physical impairment of spina bifida depend on?
Location of defect
- Leg weakness
- Bladder and bowel incontinence
- Sexual dysfunction
What is cleft lip caused by?
Failure of fusion by 12th week
- Midline clefts associated with higher rates of genetic conditions
Most are isolated (no other defects)
