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. 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.

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

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).

Nowadays, fetoscopy (examination of the fetus with an endoscopic camera) and laser removal of connections (laser photocoagulation) of the vessels connecting both fetuses are used to treat cases of twin-to-twin transfusion syndrome (TTTS). Fetoscopic laser surgery is currently the primary treatment method used worldwide. Thanks to it, the chances of survival of both fetuses can be significantly increased, and the likelihood of neurological damage in infants can be reduced. To date, laser photocoagulation is proven to be superior to old methods or the complete absence of any intervention. That all makes it the central treatment method today.

Fetoscopic laser ablation of placental vessels in twin-to-twin transfusion syndrome (taken from the website of the Johns Hopkins University School of Medicine).

Although fetoscopic laser operations increase the chances of survival of infants, as well as reduce the likelihood of neurological damage, we should also keep in mind that such surgeries can lead to twin anemia polycythemia sequence (TAPS) and other similar problems, so we cannot count on absolute success after each operation.

Twin-to-twin transfusion syndrome is a dangerous anomaly. The severity of this syndrome varies, and in more severe cases, the absence of any intervention leads to the alternate death of both fetuses.

During a twin pregnancy with a single placenta (monochorionic pregnancy), connective vessels can form between the veins that come from the same single placenta (anastomosis). Thus, the blood pumped by the heart of one fetus can flow in excess to the second fetus, which leads to the development of twin-to-twin transfusion syndrome.

Twin-to-twin transfusion syndrome does not cause any pain in the mother. However, due to an excess of amniotic fluid in one of the infants (polyhydramnios), the uterus can be very stretched. In this case, the mother may feel pain.

When treating patients using the fetoscopic laser method, the doctors who perform the surgery personally inform the families about possible problems after each surgery. Pregnant women should take into account the possible risks of premature birth, loss of water, bleeding, infections, etc.

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