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Twin-to-Twin
Transfusion Syndrome

When Two or More Babies
Share a Placenta

By Alexandria Powell

Twin-to-twin transfusion syndrome, or TTTS, is a disease of the placenta. It can affect identical twin pregnancies or higher order multiple pregnancies in which two or more of the babies are monochorionic, or share a placenta.

In TTTS, blood passes disproportionately from one baby to the other via connecting blood vessels within their shared placenta. This means that one baby, the recipient twin, gets too much blood, while the donor twin doesn't get enough blood, putting both at risk for serious injury or death.

"We know that in pretty much every monochorionic pregnancy there are vascular communications between the twins," says Dr. Francois Luks of the Brown University Fetal Medicine Program. "In about 20 to 25 percent of these pregnancies, some degree of TTTS occurs. In about 10 to 15 percent, it's severe."

Both twins try to adapt. The donor twin's body works to conserve fluid and energy, leading to oligohydramnios, or low amniotic fluid, and intrauterine growth retardation, or IUGR. As the condition worsens, the donor twin's fluid output may become so low that he or she is literally "stuck" to the side of the uterus.

The recipient's body tries to get rid of the excess fluid by increasing urination, which leads to polyhydramnios, or excess amniotic fluid. The recipient is also dealing with an excess of blood cells, leading to complications of increased blood volume and abnormal blood thickness, or hyperviscosity.

And as the recipient puts out more and more fluid, the uterus begins to stretch dangerously, and pressure is put on the mother's cervix, often leading to preterm labor and premature rupture of membranes. Both donor and recipient are likely to be very fragile and have a tough time coping with the demands of prematurity.

TTTS is diagnosed via ultrasound, although some mothers may notice symptoms such as fatigue, pressure in the belly or back and a sudden increase in the size of their abdomen. A staging system is used to diagnose the severity of the disease and to determine treatment. Stage I is the least severe form of TTTS, and Stage V is the most severe.

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• Vanishing Twin Syndrome: A Mysterious Occurrence in Multiple Pregnancies
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