Twin to Twin Transfusion Syndrome (TTTS) and other complications of monochorionic (shared placenta) twin pregnancies like unequal placental sharing are generally diagnosed by ultrasound. These problems do not occur in twins who have two placentas (dichorionic, DC), and therefore it is important to distinguish between MC and DC twins at an ultrasound examination. The earlier in pregnancy, the easier this can be achieved.
TTTS is a serious, progressive disorder that affects up to 15% of MC twins. The twins do not have malformations, but one transfuses the other through a particular blood vessel connection. In this situation, an artery from the donor twin enters the placental substance to exchange oxygen and nutrients. Unfortunately, the corresponding vein returns "by mistake" to the other twin (the recipient) via this arterio-venous connection.
In Twin to Twin Transfusion Syndrome (TTTS) the donor twin responds by partially shutting down blood supply to many of its internal organs, especially the kidneys, has reduced urine output and therefore a small amniotic fluid volume (oligohydramnios) in its amniotic cavity. The recipient responds to the blood transfusion by producing excessive amounts of urine, and is surrounded by a large volume of amniotic fluid (polyhydramnios). It is the combination of oligohydramnios/polyhydramnios that suggests the diagnosis of TTTS.
The twins are often discrepant in size, as well, with significant discordance in estimated fetal weights. The recipient's blood becomes thick and difficult to pump around the body, and this can result in heart failure, generalized soft tissue swelling (hydrops) and fetal death. Because of the blood vessel connections across the placenta, if one twin dies, the co-twin faces significant risk for death or damage to vital organs. If a co-twin survives, there is a high risk of brain injury. Without treatment, about 70-80% of twins with TTTS will die. Survivors may have injuries to their brains, hearts and kidneys.
In cases with extreme fetal hydrops, the mother may be at risk for maternal mirror syndrome, which is a condition where the mother's condition mimics that of the sick fetus. Because of a hyperdynamic cardiovascular state, the mother develops symptoms that are similar to pre-eclampsia and may include vomiting, hypertension, peripheral edema, proteinuria and pulmonary edema. Despite resection of the anomaly, maternal mirror syndrome may still occur.
The severity of Twin to Twin Transfusion is based on the stage in pregnancy during which it becomes evident (the earlier the more serious it is). In addition the degree of fluid imbalance is important in grading or staging the problem. A serious situation is associated with a deepest pocket of ultrasound measurable fluid in the sac of the donor of less than 2cm, and greater than 8cm in the recipient. A bladder that is unfilled in the donor and evidence of heart failure in the recipient are also very serious signs. The most serious situation is when in addition to this there is abnormal blood flow in the umbilical cords of the twins, measured with ultrasound. Finally evidence of heart failure (hydrops) in the recipient is the gravest situation.
Because Twin to Twin Transfusion Syndrome (TTTS) is a progressive disorder, early treatment may prevent complications, including preterm labor and premature rupture of membranes secondary to polyhydramnios. The most commonly used treatment is amnioreduction (serial large-volume amniocenteses) via Fetal Image-Guided Surgery (FIGS-IT), in which large volumes of amniotic fluid are drained with a needle placed through the abdomen of the mother into the sac of the recipient twin. This procedure may be repeated, if necessary. Survival rates with this treatment reach about 60%. Although it is not known exactly how amnioreduction improves the state of both twins, it is effective in many cases.
However, some cases of TTTS do not respond to amnioreduction, and one or both of fetuses may die if other methods are not tried. These cases are appropriately treated with a direct approach to try to stop transfusion in the abnormal arterio-venous connection. This can be achieved by using FETENDO Fetal Surgery introducing a thin fiber-optic scope through the mother's abdomen, through the wall of the uterus and into the amniotic cavity of the recipient. By examining the surface placental vessels directly, the abnormal vascular connections can be found and eliminated by directing a laser beam at them. The procedure should be as selective as possible, and detailed ultrasound examination prior to the procedure may help locate the abnormal connection, making it quicker and easier to locate with the fetoscope.