Diagnosis of twin-to-twin transfusion syndrome
Twin-to-twin transfusion syndrome is diagnosed with the aid of ultrasound. The donor foetus has very little fluid in its amniotic sac (oligohydramnios) and its bladder is either undetectable or abnormally small because it produces hardly any urine. The recipient, on the other hand, tends to have a large volume of amniotic fluid in its sac (polyhydramnios) and a very swollen bladder due to increased urine production.
There is sometimes an obvious disparity between the foetuses in terms of estimated weight and size, the recipient being larger than the donor; however, in itself this does not represent a diagnostic criterion.
Two essential criteria must be met before making the diagnosis:
Polyhydramnios in the amniotic sac of the recipient foetus. Polyhydramnios is diagnosed when the height of the largest vertical column of amniotic fluid exceeds 8 cm.
Oligohydramnios in the amniotic sac of the donor foetus. Oligohydramnios is defined as a largest vertical column of amniotic fluid of less than 2 cm.
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