Pathology of Twinning

Question 1

Types of twinning

Answer 1

• Dichorionic diamnionic (amnions may be fused)
  
  • Monozygotic (split <3 d postconception) or dizygotic
• Monochorionic Diamnionic (75% of twins)
  
  • Monozygotic
• Monochorionic Monoamnionic
  
  • “MOMO”
  • Monozygotic (>8 d postconception)

Question 2

Common/rates of complications with twinning

Answer 2

• 3x risk for fetal anomalies (Most commonly occurs w/one umbilical artery)
• 10% mortality rate
• Twin-twin transfusion syndrome
• increased maternal complications.

Question 3

Common complication in monochorionic diamniotic

Answer 3

• Twin twin transfusion syndrome: abnormal sharing of fetal circulations through an arteriovenous shunt results in a disparity in fetal blood volumes
• almost exclusively effects mono-di twins
• Donor twin gets wee and dehydrated and anemic and pale
• Recipient twin is engorged and plethoric
• Abnormal cord insertion common
• Single umbilical artery

Question 4

Common complication in monochorionic monoamniotic

Answer 4

• Twintwin transfusion syndrome: less common in MoMo due to many anastomoses
• Up to 40% perinatal fatality from any cause

Question 5

Pathophysiology of twin-twin transfusion syndrome

Answer 5

• monochorionic pregnancies there are many inter-twin vascular connections that do not exist in other twin pregnancies.
• arteries coming from one fetus can connect to veins leading to the other fetus → imbalance
• imbalance of blood flow between the two fetuses one baby becomes overperfused, plethoric and has polyhydramnios (the recipient twin)
• while the donor twin becomes growth restricted, anemic and can have oligohydramnios.
• Donor commonly known as STUCK twin (saranwrapped to the placenta) w/ anhydramnios, renal failure and IUGR

Question 6

Dizygotic twin definition/characteristics

Answer 6

• Dizygotic (“Fraternal”)
• •2 ova fertilized by 2 sperm
• •Not genetically identical
• •~70% of spontaneous twins
• •~95% of ART twins

Question 7

Monozygotic twin definition/characteristics

Answer 7

• Monozygotic (“Identical”)
• •1 ovum fertilized by 1 sperm, fertilized oocyte divides
• •Genetically identical
• •~30% of spontaneous twins
• •3-5/1000 births

Question 8

Characteristics for determining chorionicity

Answer 8

• Dichorionic/Diamniotic
  
  • -thick dividing membrane
  • -“twin peak” or “lambda” sign
• Monochorionic/Diamniotic
  
  • -thin dividing membrane
  • -“T” sign

Question 9

Appearance of dichorionic placentas

Answer 9

Question 10

Appearance of monochorionic placenta

Answer 10

Question 11

Treatment options for twin-twin transfusion syndrome

Answer 11

• Reduction amniocentesis
• microseptostomy
• laser ablation

Question 12

Characteristics of reduction amniocentesis

Answer 12

• –Removal of excess fluid from recipient twin sac using needle through mom’s abdomen
• •Up to 3L may be removed at one time
• •Repeated every few days to weekly
• –Usually early delivery (29-30 weeks)
• –Survival 18-83%

Question 13

Characteristics of microseptostomy

Answer 13

• –Creation of hole between the babies’ sacs
  
  • •Fluid moves into donor twin to equalize
• –If hole gets larger, umbilical cords may become entangled
• –80% survival of at least one twin and 60% survival of both twins in one study

Question 14

Characteristics of laser ablation

Answer 14

• –Direct visualization of communicating vessels and ablation with laser
• –Higher complication rate (15-20%)
• –70-80% survival of at least one twin and 35% survival of both
  
  • •If demise of one twin, lower rate of mortality for surviving twin (35% à 7%)