L45 Embryological Basis of Disease

Question 1

What are the pregnancy points of screening?

Answer 1

There are commonly 2 main points of screening.

The first trimester and the second trimester. If you wait until the third trimester, the options are decreased.

Question 2

When is first trimester screening done?

Answer 2

10 - 14 week

Question 3

What does first trimester screening screen for?

Answer 3

This screen looks at the foetus structurally. It is also used to calculate the gestational age (it is most accurate from 11-14 weeks) and to calculate the gestational age.

Question 4

What is first trimester screening composed of?

Answer 4

Combined screening test: a ultrasound scan and blood test.

- The USS looks at nuchal translucency - skin thickness at the back of the neck. It is a bit of oedema that appears black on USS. It is commonly raised in the trisomy. It relates also to cardiac conditions. There is a blockage of the lymphatic system (or it has not developed properly) leading to an excessive build up here. Later on in pregnancy the placenta resistance has fallen and the lymphatic system has developed further and can mimic these effects.  Alongside blood test, there is standard testing for the Trisomy's - the most common being Trisomy 21, Trisomy 18 and Trisomy 13.

Question 5

Give details of trisomy 21.

Answer 5

• The most common 1 in 800 pregnancies
  
  • Down’s syndrome
  • The incidence does vary depending on the age - it greatest in older women.
  • Caused by non-disjunction - inability of a chromosome to split - (92%) or translocation (4%)
  • Approx. 92% of affected pregnancies in the UK are terminated
  • Nearly always have some form of physical and intellectual disability - the severity is difficult to predict. Intellectual disability can be mild-severe
  • 40% of patients have congenital heart disease with 80% being atrioventricular defect /ventricular septal defects
  • Typical phenotypical characteristics:
    · Small chin, slanted eyes, flat nasal bridge, single palmer crease, large tongue.
    · Shorter stature.
    · Sleep apnoea
  • Also may have visual problems inc. cataracts (80%)
  • Hearing problems (90%)
  • Can live a very good semi-independent life
  • Must offer a termination - therefore ethical dilemma as to who you offer certain options. This is why the termination rate is high as counselling is hard

Question 6

Give details of trisomy 18.

Answer 6

Trisomy 18
- Edwards Syndrome
- 1 in 3-5000 pregnancies
- Most commonly formed by non-disjunction
- Cary a very poor prognosis
- 60% will die in utero and almost all will die within 1 year of age - median life span is 5-15 days
Typically have a small stature, microcephaly, cleft lip, muscle contracture (tightly clenched fits), small ears and jaws

Question 7

Give details of trisomy 13.

Answer 7

risomy 13
- Patau’s Syndrome
- Most commonly caused by non-disjunction - is affected by age
- Has a very poor prognosis - often incompatible with life. Most will die in utero. Lifespan is generally around 12 days.
- Rare - 1 in 10,000
Associated with severe mental disability, small stature, seizures and facial clefts

Question 8

What other conditions are screened for in the first trimester?

Answer 8

• Anencephaly: Acrania is the interruption of the ossification - nothing to do with the brain - it is ill formed bones of the skulls. This leads to herniation of brain contents. As the baby moves around it leads to lose of brain contents - leads to a frog face appearance. This has a 100% mortality. 95% detection rate in the first trimester.
• Gestational problems such as gastroschisis and omphalocele

Question 9

What is the difference between physiological and abnormal herniation?

Answer 9

Derives from the endoderm from week 3. Made of the foregut, midgut and hindgut - each with their own blood supply. During the 6th week the midgut protrudes through the umbilical cord - this is physiological herniation which allows 270 degree rotation anticlockwise. This is complete by week 12. Accurate dating is needed as if found before 12 weeks it is physiological, if found after 12 weeks there it may be abnormal herniation.

Question 10

When does second trimester screening take place?

Answer 10

Looking more for structural defects. It includes a detailed examination of the heart and brain. Generally taken from 18-26 weeks.

Question 11

What does second trimester screening screen for?

Answer 11

Looking for more structural defects. Specific conditions include:

• Spina bifida
• Cleft
• Cardiac defects

Question 12

What is the difference between gastroschisis and omphalocele?

Answer 12

Both omphalocele and gastroschisis share one major characteristic. In both conditions, a baby’s intestines extend out of a hole in the belly. In some cases, other organs like the liver or stomach also push out through the hole. In gastroschisis the intestines is not protected by the perineum but it is in an omphalocele. In omphalocele the intestine protrude from the umbilicus whereas in gastroschisis, the intestines protrude due to the anterior abdominal wall not closing properly and so a hole next to the umbilicus. Omphalocele is associated with a worse prognosis. Gastroschisis is more common.