Twin to Twin Transfusion Syndrome
Twin to Twin Transfusion Syndrome (TTTS) may be a prenatal condition during which twins share unequal amounts of the placenta’s blood supply leading to the 2 fetuses growing at different rates. 70% of identical twins share a placenta, and 15-20% of these pregnancies are affected by TTTS. TTTS isn't associated with anything the mother did or didn't do during pregnancy.
Identical twins share one placenta. Most commonly, they're in several sacs of fluid, the amniotic sacs. This type of twin pregnancy is called monochorionic (one placenta) and diamniotic (two sacs). In monochorionic, diamniotic twins (mo-di twins), there are shared blood vessels, which run from one twin to the other on the surface of the placenta. Most often internet flow of blood between the twins is fairly even, but when there's an imbalance of blood flow across these blood vessels, such one twin is getting more blood supply than the opposite , then TTTS can occur. The fetus with more blood flow is named the recipient twin, and therefore the fetus with less is named the donor twin.
Because the donor twin has less blood flow, this baby grows slower and is smaller. The baby acts dehydrated and can't make much urine. Thus, the bladder is little or invisible and therefore the amnionic fluid begins to say no . The recipient twin, however, has an excessive amount of blood flow. It grows faster and is larger than the other twin. The recipient baby tries to urinate the excess fluid from having more blood, so it has an enlarged bladder and too much amniotic fluid.
The Stages of TTTS
There are five stages of TTTS.
Ø Stage 1: There is an imbalance of amniotic fluid, with a small amount (8cm). The twins are often more than 20% different in size.
Ø Stage 2: The bladder of the donor twin is not visible or it does not fill with urine during an ultrasound exam.
Ø Stage 3: The imbalance of blood flow starts to affect the heart function in one or both babies. This is seen in abnormal blood flow in the umbilical cords or hearts of the twins.
Ø Stage 4: The imbalance of blood flow causes signs of heart failure in one of the twins.
Ø Stage 5: One or both of the twins has gave up the ghost from severe TTTS.
For Stage 1 cases, observation could also be all that's necessary, except for Stage 2 or higher cases, fetal surgery could also be the simplest option.
How is TTTS diagnosed?
A routine prenatal ultrasound will show whether there are twins in a pregnancy, and we can see if the twins are identical and sharing a placenta. This is a critical determination because if so, your babies are at risk for developing TTTS (15-20% risk).
If signs of TTTS develop, such as different amniotic fluid levels or growth differences, then ultrasounds can be performed more frequently to determine if the TTTS is really progressing. We will determine what stage of TTTS is present. A fetal echocardiogram (echo) gives us much more information about the heart function and anatomy. Your treatment options depend on the stage of TTTS, and range from observation to placental laser surgery.
How does TTTS affect my baby after delivery?
Twins with untreated advanced stages of TTTS during pregnancy usually do not do well after delivery—there is a 90% risk of fatality and, for those who do survive, a 15-50% risk of neurologic handicap.
The good news, however, is that there are many treatment options during pregnancy that can significantly improve survival and lower the risk of neurologic handicaps. If your twins’ TTTS has been successfully managed and treated during pregnancy, there is a much better chance that they will be healthy babies.
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