Prenatal Mosaicism

Question 1

Trophoblast & inner cell mass?

Answer 1

• Trophoblast: forms chorion, extra-embryonic tissue (don’t contribute to fetus).
• inner cell mass: forms amnion (embryo itself).

Question 2

What to do if Level 3 mosaicism found at CVS?

Answer 2

• Follow-up amniocentesis or fetal blood analysis along with detailed ultrasound.
• Report must include statement to reflect that the level detected at analysis will not necessarily reflect proportion or the tissue distribution in fetus!

Question 3

Definition of CPM?

Answer 3

Abnormal cells restricted to the extra embryonic tissues.

Question 4

Most common trisomies that are mitotically derived CPM?

Answer 4

• 2, 3, 7, 8

Question 5

Most commonly observed trisomies that are meioricslly derived CPM?

Answer 5

• 16 & 22!

CPM May cause placental dysfunction (leading to UGR), HOWEVER placenta nearly always retains sufficient function to support fetus.

Question 6

What % of cases of autosomal trisomy in CVS is CPM?

Answer 6

80%

• Abnormal cell lines confined to: trophoblast, villus mesenchyme.

Question 7

Summary for prenatally detected mosaicism!

Answer 7

1. Risks for abnormal outcome appear very high (>69%) for mosaic trisomies for: 2, 4, 9, 16 & 22.
2. High (40-59%) for trisomies 5, 13, 14, 15, 18, 21.
3. Moderately high (20-39%) for: 6, 7, 12 & 17.

Cases with a high % abnormal cells are more likely to be assoc. with an abnormal outcome.

• Ultrasound should be performed in all prenatally diagnosed cases.
• DNA studies for UPD recommended for mosaic T6,7,11,14,15!