Twin placentas

Twin placentas often come to the pathologist... even if they are normal. In these specimens, usually, the chorion is the key; the pathologist may be able to sort-out whether the twins are monozygotic (identical) or dizygotic (fraternal).

Monozygotic vs. dizygotic

Monoamniotic-monochorionic (MoMo)

No membrane between the fetuses.
Split at approximately 7th day.
Monozygotic twins.

Diamniotic-monochorionic (DiMo)

No interposed chorion.^[1]
Always monozygotic.
Highest risk of TTTS (twin-to-twin transfusion syndrome).

Diamniotic-dichorionic (DiDi)

Most dizygotic (70%), may be monozygotic (30%).
If monozygotic -- split before 3 days.

Twin-to-twin transfusion syndrome

General

Abbreviated as TTTS.

Definition:

Monozygotic twins that share a placental disc, have vessels which cross-over between the twins that lead to a blood imbalance between the two twins.
- Only seen in monozygotic twins.
- Vascular connection may be vein-to-vein, artery-to-vein, artery-to-artery (uncommon).^[2]

Prevalence:

Seen in ~15% of monozygotic twins.^[2]

Clinical:

Donor:
- Twin: hypovolemic, oliguric, oligohydramnic, +/- anemia, +/-hypoglycemia, +/- small pale organs.
- Placental disc: large, pale.
Recipient:
- Twin: hypervolemia, polyuria, polyhydramnios, +/- hydrops fetalis, +/- CHF, hemolytic janundice, +/- large congested organs.
- Placental disc: small, firm, congested.

Gross

Large vessels that connect the two umbilical cords.

Microscopic

Features:^[3]

Artery-to-vein anatomosis - where artery and vein are associated with different umbilical cords.
Donor twin side of placenta:
- Edematous villi.
- Increased nucleated RBCs.
Recipient twin side of placenta:
- Congested.

References

↑ Sternberg, Stephen S. (1997). Histology for Pathologists (2nd ed.). Lippincott Williams & Wilkins. pp. 979. ISBN 978-0397517183.
↑ ^2.0 ^2.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 469. ISBN 978-0781765275.
↑ Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 469-70. ISBN 978-0781765275.

[Ref_H4P2_979-1] Sternberg, Stephen S. (1997). Histology for Pathologists (2nd ed.). Lippincott Williams & Wilkins. pp. 979. ISBN 978-0397517183.

[Ref_WMSP469-2] 2.0 ^2.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 469. ISBN 978-0781765275.

[Ref_WMSP469-70-3] Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 469-70. ISBN 978-0781765275.

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