Twin placentas

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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 versus dizygotic twins

Monoamniotic-monochorionic gestation

  • Abbreviated MoMo.

General

  • Split at approximately 7th day.
  • Always monozygotic twins.

Gross

  • No membrane between the fetuses - apparently clinically.

Diamniotic-monochorionic gestation

  • Abbreviated DiMo.

General

Gross

  • Thin membrane at T-zone.

Microscopic

Features:[1]

  • One chorion (no decidua) in the T-zone.

Images:

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TWIN PLACENTA, UMBILICAL CORDS AND FETAL MEMBRANES, BIRTH:
- FETAL MEMBRANES AT T-ZONE:
-- CHORION ABSENT (DIAMNIOTIC-MONOCHORIONIC GESTATION).
- TWIN A:
-- THREE VESSEL UMBILICAL CORD WITHIN NORMAL LIMITS.
-- FETAL MEMBRANES WITHIN NORMAL LIMITS.
-- PLACENTAL DISC WITH THIRD TRIMESTER VILLI WITHIN NORMAL LIMITS.
- TWIN B:
-- THREE VESSEL UMBILICAL CORD WITHIN NORMAL LIMITS.
-- FETAL MEMBRANES WITHIN NORMAL LIMITS.
-- PLACENTAL DISC WITH THIRD TRIMESTER VILLI WITHIN NORMAL LIMITS.

Diamniotic-dichorionic gestation

  • Abbreviated DiDi.

General

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

Gross

  • Thick membrane at T-zone.

Microscopic

Features:

  • Decidua interposed between two chorions.

Images:

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TWIN PLACENTA, UMBILICAL CORDS AND FETAL MEMBRANES, BIRTH:
- FETAL MEMBRANES AT T-ZONE:
-- CHORION PRESENT (DIAMNIOTIC-DICHORIONIC GESTATION).
- TWIN A:
-- THREE VESSEL UMBILICAL CORD WITHIN NORMAL LIMITS.
-- FETAL MEMBRANES WITHIN NORMAL LIMITS.
-- PLACENTAL DISC WITH THIRD TRIMESTER VILLI WITHIN NORMAL LIMITS.
- TWIN B:
-- THREE VESSEL UMBILICAL CORD WITHIN NORMAL LIMITS.
-- FETAL MEMBRANES WITHIN NORMAL LIMITS.
-- PLACENTAL DISC WITH THIRD TRIMESTER VILLI WITHIN NORMAL LIMITS.

Pathology seen only in twin pregnancies

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.

See also

References

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