Twin-to-Twin Transfusion Syndrome

This information is useful for children and adults
Twin boys, possibly after treatment for twin-to-twin transfusion syndrome
Why Yale Medicine?
  • The specialists in our Fetal Care Center are skilled at diagnosing and treating twin-to-twin transfusion syndrome.
  • We are the only center in the state to offer laser fetoscopy to treat this rare condition.
  • Our care coordinator works closely with families, and we offer support services and access to multiple subspecialists.

The vast majority of pregnancies unfold in a normal and healthy way, but occasionally there are problems that require highly specialized treatment. This happens more often to women with a multiple pregnancy (or gestation) such as twins or triplets.

Twin-to-twin transfusion syndrome (TTTS) is one such challenge but Yale Medicine has unique expertise in treating this problem. Mert Ozan Bahtiyar, MD, an obstetrician-gynecologist who specializes in high-risk pregnancies and is medical director of the Yale Medicine Fetal Care Center, is the only physician in the state who performs a procedure called laser fetoscopy to cure twin-to-twin transfusion syndrome.

TTTS is a rare, in utero condition that occurs only in monochorionic twins (identical twins who share the same placenta). Attached to the inside of the uterus during pregnancy and connected to the fetus by the umbilical cord, the placenta delivers nutrients and oxygen from the mother’s blood to the developing babies.

With twin-to-twin transfusion syndrome, which occurs in 10 to 15 percent of monochorionic twin pregnancies, there is an imbalance in blood flow due to placental vessel connections. One twin (called the “donor” twin) gives too much blood to the “recipient” twin.

The extra blood causes the recipient’s kidneys to produce more urine, which creates a large bladder. This can lead to too much amniotic fluid (polyhydramnios), prenatal heart failure or excessive swelling (hydrops).  Meanwhile, the donor twin doesn’t have any or enough amniotic fluid. Amniotic fluid is essential for a baby’s development, but too much or too little of it can cause serious pregnancy complications.

Twin-to-twin transfusion syndrome is a progressive condition, meaning it gets worse if not treated appropriately. It usually develops between weeks 16 and 26 of pregnancy and can be easily detected with ultrasound.

At Yale Medicine, our Fetal Care Center is experienced at diagnosing and treating twin-to-twin transfusion syndrome.

“Twin-to-twin transfusion syndrome can be a troubling diagnosis for a patient to receive, but the good news is that we offer a procedure that has very good results,” says Dr. Bahtiyar. If no action is taken, one or both twins will die in more than 80 percent of cases.

There is no known genetic or other cause of twin-to-twin transfusion syndrome.

“We don’t know why, in some pregnancies, this develops, but not in others,” Dr. Bahtiyar says.

“Twinning,” on its own, he points out, is poorly understood and has unknown causes. The risk of complications grows with each additional baby a mother carries during pregnancy.