Twin to Twin Transfusion Syndrome (TTS)
Twin to Twin Transfusion Syndrome is a condition that only affects identical twins that share one placenta (monochorionic). Doctors estimate there is up to a 25% chance of such a pregnancy resulting in twin to twin transfusion syndrome. Male and female identical twins are affected equally, since the causes of the syndrome are not based on genetic problems, but on the actual development of the placenta.
Because placental development is the cause of TTS, there is nothing that can be done to prevent the condition. It is not caused by any action or genetic component of either parent.
When twins are affected by TTS, the blood flow through the placenta begins to "favor" one twin over the other. The twin who pumps blood for both twins, and as a result whose blood supply is compromised is called the "donor" twin, and the twin who receives too much blood is called the "recipient" twin. The terms may be misleading, however, in that such an inequity in blood flow is dangerous for both twins.
The twin who filters all of the blood for both twins (the "donor" twin) usually becomes smaller, and loses amniotic fluid because he/she isn't urinating properly into the amniotic sac. This twin also does not develop well, because all of its energy goes into the blood filtering process.
The twin who receives too much blood (the "recipient" twin) usually becomes larger, but undergoes stress because he/she is developing too quickly, too much blood is traveling through his/her body, and his/her amniotic fluid is excessive.
TTS can occur at any time in the pregnancy, and different risks are associated with different diagnostic times. If TTS is diagnosed early in the pregnancy, the babies cannot be delivered. If it occurs late in the pregnancy, the babies may be delivered early, but will still be at risk for certain complications.
Treatment options for TTS include laser surgery to repair the placenta and normalize blood flow, and septostomy, when amniotic fluid is removed from the recipient twin to equalize the size of the sacs. Unfortunately, in some cases, one twin must be sacrificed to save the other. In these cases, elective reduction or umbilical occlusion may be performed to preserve the life and/or health of the healthier baby.
While treatment options are limited, they are essential. Left untreated, more than 80% of TTS babies will not survive past birth. With treatment, the likelihood of one or both babies surviving TTS increases greatly. For this reason and others, women carrying identical twins should make sure they are receiving the best prenatal care possible.
For more information and support on TTS, check out these great organizations:
The Twin-To-Twin Transfusion Syndrome Foundation
Twin to Twin Transfusion Syndrome Australia
Twin2Twin: The UK Twin to Twin Transfusion Syndrome Association