Prenatal Diagnosis – Ultrasound Scan, Amniocentesis & Chorionic Villus Sampling

Question 1

What is the purpose of prenatal diagnosis?

Answer 1

To detect congenital malformations and genetic disorders before birth.

Question 2

List four common indications for prenatal diagnosis.

Answer 2

Advanced maternal age, previous chromosomal anomaly, family history of inherited conditions, balanced chromosomal translocations.

Question 3

Why is counselling important in prenatal diagnosis?

Answer 3

To support decision-making and obtain informed consent before and after testing.

Question 4

What characteristics should a good screening procedure have?

Answer 4

Simple, inexpensive, completely safe.

Question 5

Give three examples of screening procedures.

Answer 5

Family history, ultrasound scan, maternal serum biochemistry.

Question 6

What are specific diagnostic tests used in prenatal diagnosis?

Answer 6

Amniocentesis, chorionic villus sampling (CVS), fetal blood sampling.

Question 7

What is the mainstay of non-invasive screening for chromosomal anomalies?

Answer 7

Maternal serum biochemistry, particularly MSAFP.

Question 8

What gestational age is appropriate for Maternal Serum Alpha-Fetoprotein (MSAFP) testing?

Answer 8

Between 15 and 20 weeks gestation.

Question 9

What is considered a significantly elevated MSAFP value?

Answer 9

2.0 or 2.5 multiples of the median (MoM).

Question 10

List five causes of high MSAFP.

Answer 10

Miscalculated gestational age, multiple pregnancy, threatened abortion, neural tube defect, abdominal wall defects.

Question 11

What is the triple test for Down syndrome screening?

Answer 11

MSAFP, unconjugated oestriol, and β-HCG.

Question 12

What are the typical results of the triple test in Down syndrome?

Answer 12

Low MSAFP and oestriol; high β-HCG.

Question 13

What is added in the quadruple test for Down syndrome?

Answer 13

Inhibin A.

Question 14

What is the detection rate and false positive rate of the quadruple test?

Answer 14

Detection rate: 79%; False positive rate: 7.5%.

Question 15

What are the serum markers in Edwards syndrome (Trisomy 18)?

Answer 15

MSAFP, unconjugated oestriol, and β-HCG – all low.

Question 16

When are PAPPA and β-HCG best assessed?

Answer 16

11 to 13 weeks + 6 days.

Question 17

When is amniocentesis typically performed?

Answer 17

Typically at 16 weeks (15–20 weeks).

Question 18

What is the miscarriage risk for amniocentesis?

Answer 18

0.5–1%.

Question 19

How is CVS performed and when?

Answer 19

Sampling via cervix or abdomen at 10–12 weeks.

Question 20

What is the miscarriage rate associated with CVS?

Answer 20

2–6%.

Question 21

What is cordocentesis (PUBS) and when is it done?

Answer 21

Percutaneous umbilical blood sampling; at ~19 weeks.

Question 22

What is the typical target vessel for cordocentesis?

Answer 22

Umbilical vein at cord insertion into placenta.

Question 23

List three indications for cordocentesis.

Answer 23

Prenatal diagnosis of haemoglobinopathies, coagulopathies, rapid karyotyping.

Question 24

What are the advantages of identifying anomalies in utero?

Answer 24

Allows decision on termination, preparation for care, delivery in specialist unit, or intrauterine therapy.

Question 25

Which genetic disorders are common in specific ethnic groups?

Answer 25

SCD – Africans; Alpha thalassemia – SE Asians; Beta thalassemia – Mediterranean; CF – Caucasians; Tay-Sachs – Ashkenazi Jews.

Question 26

What does nuchal translucency measurement >2.5mm suggest?

Answer 26

Possible chromosomal anomaly (e.g., Down syndrome).

Question 27

When is the 2nd trimester anomaly scan typically performed?

Answer 27

18–20 weeks.

Question 28

When is a foetal cardiac anomaly scan best done?

Answer 28

At 22 weeks.

Question 29

What does an elevated β-HCG in the triple test suggest?

Answer 29

Suggestive of Down syndrome.

Question 30

What is the main goal of prenatal diagnosis?

Answer 30

To provide accurate diagnosis and offer informed choices to couples.