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AMNIONICITY |
DIAMNIOTIC TWINS |
1.
Dichorionic
diamniotic pregnancies – thick membrane composed of two layers of amnion
and two layers of chorion.
2.
Monoamniotic
pregnancies – membrane is thinner as it is only composed of two layers of
amnion
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Monochorionic Diamniotic membrane |
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Dichorionic Diamniotic membrane |
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3D Monochorionic Monoamniotic twins |
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3.
The presence
of a “stuck twin” confirms that the twins are dichorionic even in
the absence of a visible membrane. The amnion lies in contact with the fetal
body and cannot be separated as a separate structure.
4.
Complications
of monochorionic diamniotic twins:
o
Twin-twin transfusion syndrome
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Acrania acardia (TRAP sequence)
MONOAMNIOTIC TWINS |
1.
Splitting of
the embryonic mass after day 9 of fertilization results in monoamniotic twins.
2.
In these
cases, there is a single amniotic cavity with a single placenta and the two
umbilical cords insert close to each other.
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5.
Entangled
umbilical cord or fetal parts is diagnostic.
6.
A single
umbilical cord (with greater than 3 vessels), shared fetal organs and
continuous fetal skin is classical of conjoined twins which are always
monoamniotic.
7.
Monoamniotic twins are found in about 1%
of all twins or about 5% of monochorionic twins.
8. In
monoamniotic twins, the fetal loss rate is about 50–75%:
9. Complications
of monochorionic monoamniotic twins: