What is twin-to twin transfusion syndrome, and should I be worried about it?

Twin-to-twin transfusion syndrome is a very serious complication of twins with one placenta. It occurs in about 15 to 20 percent of these pregnancies. It does not occur when there are two placentas. It occurs most frequently between 15 to 25 weeks gestation and can be diagnosed only by ultrasound.

TTTS occurs because there are connections in the placenta between the circulation of baby A and baby B. They share their blood supply, and there are arteries from A that connect to arteries from B, veins from A connecting to veins of B, and arteries from A connecting to veins of B and arteries of B connecting to veins of A.

The problem develops when there is an imbalance in the blood flow going to each baby. If A gets 60 percent of the blood flow and B gets 40 percent, that might be enough to cause a volume overload of baby A and too little volume in the circulation of baby B. Baby B grows smaller and becomes the donor. Baby A gets too much blood and becomes the recipient.

The amniotic fluid around the donor disappears, and the baby becomes wrapped in its sac with little or no fluid. The recipient develops too much amniotic fluid (called polyhydramnios), and this can lead to ruptured membranes or preterm labor and delivery. As TTTS gets worse, both babies are at risk of dying in utero. This syndrome can develop in as little as 10 days to two weeks, so ultrasound exams are necessary every two weeks from 15 to 25 weeks gestation to diagnose it.

There are two treatments for TTTS. One is amniocentesis, and the other is laser surgery to cauterize the connections between the babies. Your physician will work with a perinatologist to determine the best management. The important thing is to know if you are at risk. To know that, the number of placentas must be determined. This is not done in a surprising number of twin pregnancies, especially if a radiologist is doing the ultrasound exams. If the doctor cannot tell if it is one or two placentas you should be managed as if you have only one placenta. That is safer. The TTTS Foundation is a support group with information and resources.