Placenta
Nonneoplastic placental conditions and abnormalities
Placental findings in specific conditions
Twins
Author: Mandolin S. Ziadie, M.D.
Topic Completed: 1 November 2011
Minor changes: 28 October 2020
Copyright: 2002-2021, PathologyOutlines.com, Inc.
PubMed Search: Twins placenta[title]
Table of Contents
Definition / general | Diagrams / tables | Clinical features | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) imagesCite this page: Ziadie MS. Twins. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/placentatwins.html. Accessed November 29th, 2021.
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
Images hosted on other servers:
Twinning
Clinical features
- Acardia:
- Malformed acardiac twin that is perfused by a normal twin
- Usually has a single umbilical artery
- Seen in 1% of monozygotic twin gestations
- Case report: cardiac twinning in dichorionic twin placentas (Hum Pathol 1998;29:1028)
- Fetus papyraceus:
- Early intrauterine death of one twin which undergoes extensive maceration and mummification
- If early enough, it may become absorbed into the placental disc / membranes
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
Gross images
Images hosted on other servers:
Twin placenta - acardia
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
Images hosted on other servers:
DiDi
MoDi
