Twin-to-twin transfusion syndrome

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at October 1, 2016
StartDiseasesTwin-to-twin transfusion syndrome

Twin-to-twin transfusion syndrome is a medical condition that affects a small percentage of pregnancies. It specifically affects identical twins as they develop in one placenta. Blood does not flow properly to both fetuses due to blood vessel connections that are abnormal. 


Definition & Facts

When an expectant mother is diagnosed with twin-to-twin transfusion syndrome, it is a serious matter. It is actually considered a disease that affects the placenta and the identical twins who share that placenta. The umbilical cords of both babies become connected by abnormal blood vessels. The condition can lead to failure to thrive for one of the twins due to an inadequate flow of blood and nutrients.

Twins who share one placenta do not always develop this condition. This condition can affect pregnancies involving multiple births. It can lead to a transfusion of blood from one twin to the other, giving the condition its name. When this happens, the twin that receives donated blood will receive too much blood while the other twin does not have enough blood to develop properly.

As a twin donates blood, it is likely to release less urine into the womb, a necessary component for amniotic fluid. The twin receiving too much blood is at risk as well. Heart failure is a major concern because the baby cannot handle the high level of blood. Too much urine is another issue, resulting in excess amniotic fluid.

Twin-to-twin transfusion syndrome can occur at any point during pregnancy. It often sets in during the earlier phases of pregnancy, at some point between 12 weeks and 26 weeks. However, the condition could strike during the last trimester. In some cases, it develops suddenly during labor. 

Symptoms & Complaints

In some cases of twin-to-twin transfusion syndrome, the pregnant mother will have visible signs that something isn't right with her pregnancy.

Her womb may become abnormally enlarged or seem like it has grown suddenly. If the size of the uterus is larger than it should be for the stage of pregnancy, twin-to-twin syndrome could be to blame.

The mother may develop swelling in the legs and hands (edema). Sudden weight gain may indicate that there is an abnormal increase in amniotic fluid. Cramping in the abdomen and contractions are other symptoms of concern.

An obstetric ultrasound can indicate that there are problems as well. If there is only one placenta present, twin-to-twin transfusion syndrome is likely. Otherwise, there may be excess amniotic fluid in one baby's placenta while the other does not have enough.


Twin-to-twin transfusion syndrome is a medical mystery. It is not caused by genetic factors and is not a hereditary concern. An expectant mother is not to blame for the condition. It is not caused by a mother's actions while she is awaiting the delivery of her twins or multiple babies.

The condition is more common for pregnancies in which only one placenta develops and the babies are sharing it in the womb. It is considered completely random and it is believed that the abnormal blood vessels may develop as soon as the placenta forms. When they actually cause a problem differs for each pregnancy.

Diagnosis & Tests

Twin-to-twin transfusion syndrome should be diagnosed as soon as possible in order to deliver healthy babies. If it is not caught in time, major birth defects or death can result. Early screening is recommended for any mother who is having twins or multiple births. If a mother has only one placenta and there is more than one fetus, she should be closely monitored.

A nuchal translucency ultrasound can detect problems with the placenta during the first trimester. From that point on, ultrasounds should be performed every one to two weeks throughout the pregnancy to ensure the babies are developing properly and there is not a concern with the placenta or blood flow.

Treatment & Therapy

Several treatments are possible in pregnancies involving twin-to-twin transfusion syndrome. In some cases, the only necessary treatment may be a draining of excess amniotic fluid for one of the twins in order to relieve pressure and restore balance in the womb.

If the condition occurs later in the pregnancy and the babies can safely be delivered, pregnancy may be induced or a cesarean section could be recommended. In cases where the condition has been detected in the early stage of pregnancy, premature delivery may not be possible.

Laser ablation can be used in which a laser targets the abnormal blood vessels that are being shared by the babies. The blood vessels are cut through the use of the laser and they are effectively sealed. From this point forward, the twins can have normal blood flow. 

Prevention & Prophylaxis

Unfortunately, there is no known way that an expecting mother can prevent twin-to-twin transfusion syndrome, nor is it possible to save every baby affected by this condition. The earlier the detection, the earlier treatment can be initiated in an effort to save the lives of the fetuses. The hope is to prevent birth defects as well, although there are no guarantees.

An expecting mother needs to be proactive. If a mother is told that she is having twins, it is vital that she ask questions and remain aware of any changes, especially if there is abnormal swelling of the hands, feet, or abdomen. Early contractions could be a sign that there is a problem. Regular ultrasounds are advised in order to facilitate prenatal diagnosis.

While it may not be possible to prevent twin-to-twin transfusion syndrome from happening, an expectant mother can take action as soon as possible when the condition is diagnosed. Early intervention can result in the delivery of two, healthy babies, even if they must be delivered earlier than expected. It is important to be especially vigilant if there is only one placenta, as twins sharing a placenta are at a greater risk.