T2 L11: Prenatal screening

Question 1

What is the scan at 10-14 weeks for?

Answer 1

• To check for viability
• Accurate dating
• Multiple pregnancy
• Diagnosis of major structural abnormalities like spina bifida, anencephaly, exomphalos, bladder outflow obstruction
• Screening for chromosomal conditions

2-3% women will have miscarried by this point

Question 2

Why is accurate dating important?

Answer 2

It’s needed for screening and reduces induction of labour at the wrong time

Question 3

In which type of multiple pregnancy is there a membrane between the babies?

Answer 3

In dichorionic twins (from different eggs)

In monochorionic twins there is no membrane because the babies split from the same egg

Question 4

What is trisomy 21?

Answer 4

Down’s syndrome

It’s the most common type of chromosomal condition

Question 5

What is trisomy 18?

Answer 5

Edward’s syndrome

Question 6

What is trisomy 13?

Answer 6

Patau’s syndrome

It’s the least common type of chromosomal condition

Question 7

What are the symptoms of Edwards syndrome?

Answer 7

Microcephaly (small and abnormally shaped head)
Micrognathia (abnormally small jaw and mouth)
Long, overlapping fingers and underdeveloped fingernails.
Scrunched fists.
Low-set ears.
Arched spine and abnormally shaped chest.
Crossed legs.
Umbilical hernia

The babies don’t live long

Question 8

What are the symptoms of Patau’s syndrome?

Answer 8

cleft lip and palate.
an abnormally small eye or eyes (microphthalmia)
absence of 1 or both eyes (anophthalmia)
reduced distance between the eyes (hypotelorism)
problems with the development of the nasal passages

The babies don’t live long

Question 9

What does first trimester combines screening include?

Answer 9

It takes into account maternal age, results from a nuchal translucency scan, and PAPP-A and beta-hCG blood markers to show the chance of a baby having a chromosomal condition

Question 10

How does a Nuchal translucency (NT) scan show chromosomal abnormalities possibility?

Answer 10

If there is extra fluid, it can indicate an abnormality

Question 11

What levels of beta-hCG and PAPP-A can predict downs syndrome?

Answer 11

high free beta-hCG and low PAPP-A

Question 12

What are some influencing factors for combined screening which can obscure the results?

Answer 12

Maternal age
Gestational age
Ethnicity
Smoking
IVF
Multiple pregnancies
Maternal diabetes
Past history of chromosomal abnormalities
Fetal sex

Question 13

When is a second trimester quadruple screening test offered?

Answer 13

• Unable to measure nuchal translucency Eg. due to fetal position
• Pregnancy is too advanced

Only screens for Down’s syndrome

Question 14

What factors does a second trimester quadruple screen measure?

Answer 14

• Gestational age
• Maternal age
• Smoking
• Weight
• Ethnicity
• 4 maternal biochemical markers: UE3 unconjugated estriol (placental hormone), AFP alpha fetoprotein (protein from fetus), Inhibin A placental hormone, and beta-human chorionic gonadotrophin (BHCG placental hormone)

Question 15

Which screening test is the best for chromosomal abnormalities?

Answer 15

The combined because it has a higher detection rate than the quadruple screen

Question 16

What are the 2 diagnostic invasive tests for chromosomal abnormalities?

Answer 16

Chorionic Villus Sampling 11+ weeks
Amniocentesis 15+ weeks

Around 0.5%-1% risk of miscarriage (higher in twins)

Question 17

What does non-invasive prenatal screening involve?

Answer 17

It tests the fetal DNA in the mothers blood

Question 18

When is non-invasive prenatal screening (NIPT) offered?

Answer 18

• After a higher chance result from the combined or quadruple test
• To singleton and twin pregnancies only
• Up to 21 weeks and 6 days of pregnancy to allow time to abort is needed

Question 19

When is non-invasive prenatal screening not offered?

Answer 19

• Maternal cancer because there will be free fetal DNA from tumour
• Possibility of donor DNA Eg. after blood transfusion, organ transplant, stem cell therapy
• Vanished twin
• Known maternal trisomy 21/balanced translocation/mosaicism of T13/18/21

Question 20

What are the advantages of NIPT screening?

Answer 20

• High detection rate, low screen positive rates

- Reduced invasive diagnostic techniques

Question 21

What are the disadvantages of NIPT screening?

Answer 21

• Not diagnostic (false positives/false negatives)
• Not suitable for everybody
• Expensive
• Results can only be confirmed with invasive tests

Question 22

Which 11 conditions are screened for at the mid-trimester scan?

Answer 22

Anencephaly
Open spina bifida
Cleft lip
Diaphragmatic hernia
Gastroschisis
Exomphalos
Transposition of the great arteries
Atrioventricular septal defect
Tetralogy of fallot
Hypoplastic left heart syndrome 
Bilateral renal agenesis
Lethal skeletal dysplasia 
T13 and T18