Twinning

Question 1

What is the difference in prevalence of monozygotic and dizygotic twinning?

Answer 1

Monozygotic

• rate doesn’t vary worldwide
• 0.3%

Dizygotic (approx 1/80)
-rate increasing
-rate differers wordwide
 x highest - africa
x lowest - asia

Question 2

What determines what membranes twins share

Answer 2

Stage at which zygote is split

split as a zygote (<4days)
-diamniotic, dichorionic

4-8 days
-monochorionic,
diamniotic

Split later (8-13 days)
-monochorionic, monoamniotic

Usually split as a blastocyst

Question 3

Why might monozygotic twinning occur

Answer 3

Damage to inner cell mass

Damage to zona pellucida

Question 4

What combination of mono and dizygotic twins can you have in triplets

Answer 4

All fraternal
All identical
One set of one + another