Screening and Assessment of Genetic Disorders

Question 1

Describe the basis of pre-implantation genetic diagnosis (PGD).

Answer 1

1. 1-2 cells are removed from the embryo at around 3 days, when the embryo has 6-10 cells
2. Genetic tests are carried out on the cells, including FISH, PCR, QF-PCR etc.
3. Only healthy embryos are then implanted back into the woman (up to 2 at a time)

Question 2

Discuss the advantages (1) and disadvantages (4) of pre-implantation genetic diagnosis (PGD).

Answer 2

ADVANTAGES:
-Termination not necessary because all embryos are healthy

DISADVANTAGES:

• Long waiting times
• Not available to all women
• Multiple visits and procedures needed
• Take home baby rate less than 50%

Question 3

Give 2 examples of prenatal diagnostic tests.

When are these tests done?

How long do the results for each take?

What is the miscarriage rate?

Answer 3

Chorionic villous sampling
When: 10-12 weeks
Results: <1 week
Miscarriage: 1 in 50

Amniocentesis
When: 16-18 weeks
Results: 1-2 weeks
Miscarriage: 1 in 100