Twin Formation

Question 1

What are the 2 kinds of twin formation?

Answer 1

**Monozygotic - **identical

**Dizygotic ** - fraternal (66%)

Question 2

What are the characteristics of dizygotic twins?

Answer 2

• look different
• can be same or diff. sex
• ALWAYS: 2 amnions + 2 chorions … 2 placenta
• MAYBE: placentas fuse

Question 3

What are some characteristics of monozygotic twins?

What two situations can monozygotic twins develop from?

Answer 3

• look same
• same sex

1. separate amniotic sacs, separate chorions
2. separate amniotic sacs, same chorion

Question 4

What are the different placental situations of monozygotic twins?

Answer 4

• Shared Placenta - most common, AKA twin placenta
• **Fused Placentas ** - 2 placentas fuse, less common

Question 5

What are the types of triplets?

Answer 5

1. identical - one zygote
2. identical + singleton - two zygotes
3. fraternal - 3 zygotes

Question 6

What happens when there is a common chorion AND amnion?

Answer 6

multiple situations

1. **vanishing twin - **aka fetal resorption, 1 dies and is resorbed
2. **parasitic twin - **incompletely formed twin depends on fully formed for survival

Question 7

How are conjoined twins formed?

Answer 7

fusion of embryonic discs