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Dichorionic diamniotic twin pregnancy

A dichorionic diamniotic (DCDA) twin pregnancy is a type of twin pregnancy where each twin has its own chorionic and amnionic sacs. This type occurs most commonly with dizygotic twins, but may also occur with monozygotic twin pregnancies. This type of pregnancy may have characteristic findings on ultrasound.

Epidemiology

DCDA pregnancies account for the majority (~76%) of all twin pregnancies. They account for all dyzgotic pregnancies and ~20% of monozygotic pregnancies.

Pathophysiology

With a dizygotic pregnancy two ova are independently fertilised by two sperm leading to two zygotes. 

With a monozygotic twin pregnancy, a DCDA pregnancy results from seperation of the zygotes at ~1-4  days post fertilisation (morula) stage. 

Radiographic features

Ultrasound

Sonographic assessment of chorionicity is most accurate in the first trimester.

First trimester

Features supporting a DCDA pregnancy:

Second trimester
  • when there is no placental fusion, two seperate placental sites may be seen 4
  • a finding of two different genders for each twin is a definitive feature for a dizygotic pregnancy which in turn will invariably mean a DCDA pregnancy

If the twins are of the same gender then it is extremely difficult if not impossible to determine if they are monozygotic or dizygotic on ultrasound.

Complications

While the complication rate is still much higher with twins than with a singleton pregnancy, a DCDA pregnancy carries the lowest rate of complications amongst twin pregnancies. Such recognised complications include:


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Ultrasound

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