Placental findings in specific newborn / fetal or maternal conditions

Topic Completed: 1 November 2011

Revised: 19 February 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Twins placenta[title]

Mandolin S. Ziadie, M.D.
Page views in 2019: 5,620
Page views in 2020 to date: 714
Cite this page: Ziadie MS. Twins. website. Accessed February 18th, 2020.
Definition / general
  • 1 in 80 births in US, 1/3 are monozygous
  • Dichorionic, diamnionic: may be mono or dizygotic; lack vascular anastomoses because in cases of a single disc, the septum / dividing membrane is an area of fusion rather than a true single disc
  • Monochorionic: are monozygotic; may be diamnionic or monoamnionic, depending on timing of split
  • Monochorionic have higher mortality due to premature labor; monoamniotic have 33% perinatal mortality due to cord complications (twist, knot)
Diagrams / tables

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Gross description
  • Didi discs may be entirely separate or fused
  • When fused, fetal vessels do not cross area of fusion
  • Dividing membranes are usually thick / opaque with grossly visible blood vessels and a distinct ridge / septum where they connect to the disc

  • Mono discs may have major vascular anastomoses between the twins with arteries superficial to veins
  • It is important to document the type, size and location of anastamoses, using injection studies to show the flow of blood
  • Monochorionic diamniotic (MoDi): the dividing membranes are usually thin and translucent without a thick ridge at the point of attachment
  • Monochorionic monoamniotic (MoMo): no dividing membranes; conjoined twins fall into this category

  • Abnormalities in cord insertion (e.g. velamentous cords) are more common in twins
Microscopic (histologic) description
  • T zone is the region of the disc where the dividing (septal) membranes attach to the chorionic plate
  • Sampling this region or making a membrane roll of the dividing membranes will provide information about the type of twinning
  • DiDi (dichorionic diamniotic): "hamburger" consisting of a layer of chorion between two amniotic membranes
  • MoDi (monochorionic diamniotic): "nothing" (translucent septum) in the middle of the two amnionic layers
Microscopic (histologic) images

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