The intertwin membrane refers to a membraneous separation between two fetuses in a twin pregnancy. Depending on the chorionicity and amnionicity, the membrane may have a number of layers
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dichorionic diamniotic (DCDA) pregnancy
- composed of two chorionic and two amniotic layers
- usually has a thick (often taken as >2 mm 4) inter-twin membrane
- more reflective
- may demonstrate the twin-peak sign at its margin
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monochorionic diamniotic (MCDA) pregnancy
- composed of two amniotic layers only
- usually has a thin (often taken as <2 mm 4) inter-twin membrane
- less reflective
- may demonstrate the T sign at its margin
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monochorionic monoamniotic (MCMA) pregnancy
- no intertwin membrane