Lecture 2

Question 1

Maternal serum screening (non-invasive prenatal test)

Answer 1

Test hormone levels in mother’s blood. Low Alpha-fetoprotein (Afp) and Unconjugated estriol (UE3) plus high Human Chorionic gonadotropin (hCG) can be an indication of Down Syndrome. Triple test performed at 16 weeks.

Question 2

Ultrasonography (non-invasive prenatal test)

Answer 2

Echoes reflected from organ boundaries are converted to images on monitor. Can only identify clear physical abnormalities: eg. anencephaly (10-12 weeks), trisomy 18 and 21 (18-20 weeks).

Question 3

Amnioncentesis (Invasive prenatal test)

Answer 3

Performed at 16-18 weeks
Risk = 0.5 - 1%
Amniotic fluid is extracted from amniotic cavity with a needle. Fluid contains fetal cells which can be cultured for 14 days for karyotyping.
Results by 18-20 weeks – possible late mid-trimester termination of pregnancy through induced labour.

Question 4

Chorionic villus sampling - CVS (Invasive prenatal test)

Answer 4

Performed at 10-12 weeks
Risk = 0.5 - 2%
Catheter is inserted through cervix to collect chorionic villus cells (pre-placental cells). Cells are diving cells with no need for culturing.
Results by 10-12 weeks
Can cause major abnormalities if performed too early.

Question 5

Pre-implantation genetic diagnosis - PGID

Answer 5

Fertilization of sperm and egg cells in vitro. Cultured to blastocyst stage where one cell is collected to test for genetic abnormalities. If affected, no implantation and no termination of pregnancy.
Highly specialized and EXPENSIVE. Not available to everyone.