Twin-to-Twin Transfusion Syndrome

Thanks to new treatments and procedures, Twin-to-Twin Transfusion Syndrome—a life-threatening illness that can occur in identical twin pregnancies—is sometimes treatable, resulting in the birth of one or two healthy babies.

What Is TTTS?

Sometimes when a fertilized egg splits into two embryos, or twins, each fetus creates its own placenta from which it receives blood, nutrients, and oxygen from its mother. In some cases, the twins share a single placenta, and they each usually have an independent set of blood vessels connected to it for nourishment. Twin-to-Twin Transfusion Syndrome occurs when the identical twin fetuses not only share a placenta, but share some of the connecting blood vessels, too. Like conjoined twins (also known as Siamese Twins), the siblings share parts of their circulatory system as well as a common organ—the placenta.

This interconnection can cause one baby (the recipient) to receive too much blood. The baby's heart has to work overtime to pump all the extra blood, which can eventually lead to heart failure. On the flip side, the other baby (the donor) will have too little blood in its body, which can result in a lack of growth or even death from excessive blood loss.

Because the donor twin is receiving less blood and nourishment, it will often produce less urine and have less amniotic fluid, creating a situation known as "stuck twin syndrome," because the baby can't move due to lack of amniotic fluid. The donor twin becomes literally stuck in its dry amniotic sac. Left untreated, babies that don't die in utero are born prematurely and experience serious medical problems such as heart defects and cerebral palsy.

Risk Factors

Multiple births are on the rise in the United States, with one in 30 births resulting in twins, triplets, or more. Twin-to-Twin Transfusion Syndrome affects about 10 percent of all identical twin or higher multiple gestation pregnancies: that's nearly 4,300 pregnancies—or over 8,500 babies each year. While the actual cause of TTTS isn't known, doctors say that it's not hereditary, and it's not caused by anything either parent does or doesn't do. It's simply a random biological occurrence.

Sometimes an expectant woman will experience a rapid weight gain or a sudden swelling of the abdomen that indicates the onset of Twin-to-Twin Transfusion Syndrome, but the typical TTTS case is diagnosed during a routine ultrasound, when the obstetrician sees one twin growing much faster than the other or too much amniotic fluid around one twin and little to none around the other. Since TTTS can develop at any time during gestation, and sometimes doesn't show up until a few weeks after the normal 16- to 20-week ultrasound performed on singletons, obstetricians will often monitor identical twin pregnancies very carefully to watch for signs of unequal growth and fluid.

Because TTTS isn't always caught at the earliest opportunity, Dr. Julian E. De Lia, medical director of the International Institute for the Treatment of Twin-to-Twin Transfusion Syndrome at St. Joseph Regional Medical Center in Milwaukee, Wisconsin, says that the number of placentas can be determined by eight weeks gestation and urges anyone carrying multiples to insist that her doctor determine the number of placentas as soon as possible.