What Is Twin-to-Twin Transfusion Syndrome?

Although Twin-to-Twin Transfusion Syndrome is extremely rare, when it does occur, it’s serious and life-threatening to both infants. Receiving a diagnosis of TTTS can be devastating and overwhelming, but educating yourself about what the condition is and how it can be treated can help you better understand what to expect so you can work with your care provider.

TTTS occurs when there’s a problem with the placenta shared by identical twins. Although both twins are sharing the blood supply, they aren’t sharing it equally because of a problem with the blood vessel development within the placenta. While one fetus is receiving more than her share of the blood supply, the other fetus isn’t getting enough. That means one twin is not getting the kind of nutrients he needs to survive or to grow at a normal pace.

How Does TTTS Affect Your Fetus?

When one fetus receives too much blood, and the other receives too little, both of them are affected negatively. The fetus not receiving enough nutrient-rich blood and oxygen (referred to medically as the “donor”) will try to use what little blood he is receiving, and the blood flow will be directed to its most important organs — the brain and the heart — at the expense of less vital organs such as the kidneys. This twin is at risk for failure of the kidneys or other organs because of the lack of sufficient blood flow.

While this fetus begins producing less urine, the twin receiving too much blood (called the “recipient”) will produce a large volume of urine. That twin will also have a high amount of amniotic fluid in her amniotic sac, while the other twin has too little fluid. As that happens, the twin receiving too much blood may experience thickening of the blood, which makes it difficult to pump throughout her body. This can lead to heart failure, soft tissue swelling and other complications.

Because the twins share the placenta, if one fetus dies, it will create a significant risk for the other twin, including brain injury, damage to vital organs or even death.

What Does It Mean to Receive a TTTS Diagnosis?

A twin-to-twin transfusion syndrome diagnosis is confirmed by an ultrasound, which will show that the pocket of amniotic fluid is less than 2 centimeters in one of the twin’s sacs and more than 8 centimeters in the other sac. In addition to this diagnosis, the twins will often have significantly different weights and sizes, much of which is the result of the unequal sharing of the placenta.

TTTS causes health problems for the mother as well. Some of the other signs of TTTS can include premature contractions, dyspnea and rapid uterine growth. The fluid retention can cause the mother a great deal of discomfort and put too much pressure on the cervix, which may rupture as a result. When this happens, it results in miscarriage or preterm delivery.

The long-term outlook depends on how severe the condition is and how far it has progressed when it is diagnosed. The spectrum of severity ranges dramatically, so it requires careful follow-up and monitoring with sonograms. Knowing which stage the TTTS is at will help determine next steps, which can range from observation and monitoring to laser surgery.

What Are the Stages of TTTS?

There are five twin-to-twin transfusion syndrome stages, which are:

• Stage I: An imbalance of amniotic fluid shows that less than 2 centimeters of amniotic fluid surrounds the donor twin and more than 8 centimeters of fluid surrounds the recipient; often, there is also at least a 20% difference in the size of the twins.
• Stage II: The donor twin’s bladder is not visible or it doesn’t fill with urine during an ultrasound examination.
• Stage III: Heart function of one or both of the babies begins to be affected by the imbalanced blood flow.
• Stage IV: One of the twins shows signs of heart failure as a result of the imbalance of blood flow.
• Stage V: At least one of the twins has passed away as a result of severe twin-to-twin transfusion syndrome.

If TTTS is diagnosed, it will be monitored carefully by specialists to make sure it does not progress. Since progression can happen very rapidly, it’s important to have expert care from a team that is skilled in the early detection and treatment of twin-to-twin transfusion syndrome.

What Is the Treatment for TTTS?

The twin-to-twin transfusion syndrome treatment is based on what stage it is when it is diagnosed. In Stage I, it may not require any intervention but will involve observation to ensure that it isn’t progressing. This could include weekly ultrasounds.

Since cardiovascular issues are a leading cause of death for both the recipient and the donor twin, echocardiographs are often used to evaluate the response of the twins to treatment.

One of the most widely accepted therapies for TTTS has been serial amnioreduction, in which the excess fluid around the larger twin is removed in order to reduce the amount of pressure from the fluid and, in doing so, reduce the risk of early labor.

In recent years, the practice of fetoscopic laser photocoagulation has become more common for cases that are at Stage II and higher. In this procedure, a laser is used to block blood vessels between the twins. Now the blood flow between the two twins is blocked and each twin receives blood flow separately from the placenta, which allows each twin to receive his or her supply independent of one another.

In extreme cases, where the TTTS is in Stage IV and the donor twin will not survive, surgeons can perform cord coagulation. In this procedure, the blood supply to the donor twin is closed off so that the recipient twin will be able to survive.

What Is the Survival Rate for TTTS?

The twin-to-twin transfusion syndrome survival rate depends upon the stage at which it is diagnosed and treatment can begin. If left untreated, advanced stages of TTTS have a 90% fatality risk and, if the twins do survive, they have up to a 50% chance of having a neurological handicap.

However, the majority of babies who receive proper, early TTTS diagnosis and treatment will survive and be able to live normal, healthy lives.

The Fetal Care Center in Dallas is one of only a few centers worldwide with the capability to perform the full range of fetal interventions. If you have a question or wish to make an appointment, please call 972-566-5600 for urgent or same-day appointments. We are here for you and your family.