Twins

Question 1

Compare the location of the amnion and chorion

Answer 1

• Amnion = closer to fetus (in direct contact with amniotic fluid)
• Chorion = external to amnion

Question 2

Which are more common: dizygotic or monozygotic twins?

Answer 2

Dizygotic (fraternal) twins much more common

Question 3

Risk factors for having twin pregnancy (2)

Answer 3

Higher maternal age

Use of assistive reproductive technology

Question 4

What causes Twin Twin Transfusion Syndrome?

What types of twins can have it?

What is the consequence for each baby?

Answer 4

• Abnormal artery-vein connection creates unidirectional blood flow btwn twins
  
  • Occurs in monochorionic-diamniotic fetuses
• Recipient twin ends up with polyhydramnios
• Donor twin has oligohydramnios

Question 5

What is the cause of death in babies with twin twin transfusion syndrome?

Answer 5

Donor twin dies due to severe anemia

Recipient twin dies due to excess blood causing HF

Question 6

Compare monozygotic and dizygotic twins

(fertilization & chorion/amnion)

Answer 6

• Dizygotic twins (fraternal) = 2 eggs fertilized separately by 2 sperm
  
  • Always di-chorionic, di-amniotic
• Monozygotic twins (identical) = 1 egg fertilized by one sperm
  
  • Can be any combination of mono/di chorionic/amniotic

Question 7

If the pregnancy is dichorionic/diamniotic, is it identical or fraternal twins?

Answer 7

Most likely fraternal (more common), but you can’t tell on ultrasound

Question 8

Describe how the timing of cleavage affects chorion/amnion status of monozygotic twins

Answer 8

If cleavage occurs on…

• Day 0-4: Separate chorion and amnion
• Day 4-8: Shared chorion
• Day 8-12: Shared amnion
• Day 13+: Shared body

*SCAB

Question 9

Relationship between chorion and cyto/syncytiotrophoblast?