TTTS is a syndrome that affects the structure of the placenta. The placenta is an organ that forms during pregnancy, attaching to your uterus and providing blood and nutrients to your baby. In TTTS, there is an intrauterine blood transfusion from one fetus to the other.
There are many blood vessels in the placenta. In TTTS, abnormal blood vessels form in the placenta, and blood flows unevenly between the fetuses. TTTS leads to unequal placental sharing, which means that one baby receives more blood than the other.
This condition affects pregnancies with identical twins who share a placenta or multiples with more babies, such as triplets. As a result, one of the twins becomes a “donor,” and the other twin becomes a “recipient” of this twin-to-twin transfusion.
TTTS can affect both twins negatively. It is a progressive condition that worsens throughout the course of the pregnancy.
The donor twin receives insufficient blood, oxygen, and nutrients. This twin develops anemia, a condition characterized by a low amount of red blood cells and hemoglobin. The anemic fetus prioritizes vital organs like their brain and heart, and less vital organs become atrophied or damaged. These organs include the donor’s kidneys, and so the fetus produces less or no urine. This leads to low levels of amniotic fluid.
The donor baby also becomes dehydrated and grows more slowly. The donor twin usually has 20 percent less birth weight than the recipient twin. The donor twin’s hemoglobin may be 5 g/dL less than the recipient’s.