Twin-twin transfusion syndrome (TTTS) is a condition in which the blood passes unequally between identical twins that share a placenta (monochorionic). Monochorionic twins are a type of identical twins that share a placenta. Within the shared placenta are blood vessels that connect the blood supply of the two fetuses, allowing blood to flow between the twins. In about 15 percent of monochorionic, diamniotic (two amniotic sacs) twins, the blood flow becomes unbalanced, leading to a condition known as Twin-Twin Transfusion Syndrome (TTTS).
In twin-twin transfusion syndrome, the smaller twin (donor) pumps blood to the larger twin (recipient), causing the recipient twin to receive too much blood and the donor to receive too little. The increased volume of blood causes the recipient twin to produce more than the usual amount of urine, which can result in a large bladder, too much amniotic fluid (known as polyhydramnios) and hydrops, a prenatal form of heart failure. The donor twin produces less than the usual amount of urine, resulting in low or no amniotic fluid surrounding it (oligohydramnios) and a small or absent bladder. Without intervention, the condition can be fatal for both twins.
The most important step in evaluating a twin pregnancy for twin-twin transfusion syndrome is to determine whether the twins share a single placenta. Ultrasounds early in the pregnancy (first trimester) are best at making this distinction. Other features of TTTS include same fetal sex, and a size and amniotic fluid volume difference between the two fetuses. An anomalous twin may mimic a “stuck” twin. Selective intrauterine growth restriction (sIUGR) is a related condition that involves the same shared placenta, but different vascular connections between the two babies. A detailed sonographic assessment rules out any structural anomalies and helps to guide an individualized treatment plan.
With our growing understanding of twin-twin transfusion syndrome as a primarily cardiovascular disorder, it is also important to obtain a thorough assessment of the fetal cardiovascular system. Families visiting CHOP’s Center for Fetal Diagnosis and Treatment are scheduled for a comprehensive, one-day evaluation that will require some or all of these tests:
Management of twin-twin transfusion syndrome may include any of the following:
The results of tests and these treatments will be discussed in detail after evaluation. We are here to help.
Updated: June 2011