Twin-to-twin transfusion syndrome is a serious complication that occurs during pregnancy of twins with one placenta (monochorionic pregnancy). It happens when connective vessels are formed between the veins coming from the same placenta, which provides both fetuses with all the necessary substances for development, the blood pumped by the heart of one fetus (the donor) can flow in excess to the second fetus (the recipient). This problem was first described by the German specialist in gynecology and obstetrics Friedrich Schatz (1841-1920) and the Austrian anatomist Josef Hirtl (1810-1894) by injecting a dye into the vessels of the placenta and published in a scientific journal in 1886. Thus, this disease is known for more than a hundred years.

 

Image-1:Anatomical structure of placental vascular connections in twin-to-twin transfusion syndrome (taken and modified from the website ResearchGate.com).

 

The continuous flow of blood pumped from one fetus to other causes anemia, developmental delay, and amniotic fluid deficiency (oligohydramnios) in the donor fetus, while the recipient fetus suffers from an increase in blood volume (hypervolemia), an excess of amniotic fluid (polyhydramnios), and weight gain. If not interfered with, the process results in the death of the donor fetus due to anemia, and the death of the recipient fetus due to heart failure, caused by a large volume of blood. The death of one of the fetuses exacerbates the problem and can lead to death or severe disability of the other. The risk of infant death from twin-to-twin transfusion syndrome without any intervention is reported to be between 70 and 100 percent.

In the past, the treatment of twin-to-twin transfusion syndrome was mainly related to emptying the amniotic fluid, since the fetus that receives blood in excess also has an excessive amount of amniotic fluid, which leads to premature birth. Similarly, other treatments involve piercing the amniotic membrane separating the two fetuses and then letting the amniotic fluid flow into the area of the fetus with less fluid. Although these methods enjoyed some success, the search for a new treatment continued since the existing ones could not prevent the main problem (blood flow from one fetus to another).