How to detect TAPS before birth
Since monochorionic twin pregnancies are regarded as high risk pregnancies, biweekly ultrasound exams are planned from 14 weeks of gestation. During these exams the doctor will look at growth and blood flow of the babies.
In order to detect TAPS before birth, it is important to look at the blood flow in one of the vessels of the brain, the middle cerebral artery, using Ultrasound Doppler. In the anemic TAPS donor, the blood is very thin (as thin as lemonade) and flows quickly. The blood of the TAPS recipient is very thick (as thick as ketchup) and therefore flows slowly. When the doctor has measured the blood flows in both children, these values will show up in a graph. For the diagnosis of TAPS, there must be a large difference between the blood flow rate of the donor and the blood flow rate of the recipient.
Aside from the blood flow rate in the brain vessels, the doctor will also examine the blood flow in the vessels of the umbilical cord. When these flows are abnormal, this might indicate that the babies are actively suffering from TAPS.
Except from blood flow measurements, the doctor will also look at some other aspects on ultrasound in case of a TAPS twin.
Ultrasound findings in TAPS donors
In some TAPS donors an enlarged heart can be seen on ultrasound, as a reaction to anemia. This is called cardiomegaly. If the donor is severely affected by anemia, it can accumulate fluid in different parts of the body, such as in the pericardial cavity, under the skin (skin edema) and in the abdominal cavity (ascites). Fluid accumulation in different parts of the body is called hydrops.
Ultrasound findings in the TAPS recipient
With the TAPS recipient, special attention is given to the liver. Because the blood is very thick, this can cause congestion in the vessels. In some recipient these congested blood vessels are clearly visible as white dots in the liver. This, in combination with the grey-black appearance of the liver, can resemble a starry sky. Hence, this typical ultrasound image is referred to as a starry sky liver.
Ultrasound findings in the placenta
In case of anemia , fluid accumulation can not only develop in donors body, but also in its part of the shared placenta. This does not happen in the placental share of the recipient. This difference in placental appearance can be clearly identified on ultrasound. The placental share of the donor presents swollen, whereas the placental share of the recipient is flat and grey.
Stages of TAPS
To determine the severity of TAPS, a classification system is proposed. In stage 1 and stage 2 TAPS, a large difference in blood flow rate is seen in the brain, but with normal blood flow in the umbilical cord vessels. In case of stage 3 TAPS, not only the blood flow in de brain is abnormal, but also the umbilical cord vessels. When the donor starts to accumulate fluid in its body (hydrops), its called a stage 4 TAPS. With stage 5 TAPS, one or both babies have died.