Twin-to-twin transfusion syndrome only happens when identical twins share a placenta. Fraternal twins and identical twins with separate placentas are not at risk for TTTS.
Signs of TTTS
Twins with TTTS have different symptoms based on whether they are donors or recipients. Recipient twins receive too much blood, both from the placenta and from the other twin. These babies are larger and have excessive amniotic fluid (polyhydramnios). Because these babies have so much blood in their bodies, their circulatory systems may be overloaded, causing heart problems. Donor TTTS twins receive less blood from the placenta and lose blood to the other twin. Donor twins are smaller, both before and after birth. They are pale and anemic, have reduced urine output in utero, and smaller-than-average bladders. If the twins have two amniotic sacs, the donor twin will have reduced amniotic fluid (oligohydramnios).
Stages of TTTS
Twin to twin transfusion syndrome may be fairly mild or very serious, depending on how unevenly blood is shared by the babies. Once TTTS is diagnosed, doctors will follow the pregnancy closely to see if the symptoms are progressing or not in the following stages:
Stage I: The donor twin has reduced amniotic fluid; the recipient twin has excessive amniotic fluid.Stage II: Same as above. The donor twin’s bladder is not visible on an ultrasound—a sign of reduced urine output in utero.Stage III: All of the above symptoms are present; blood flow in the umbilical cords is abnormal.Stage IV: All of the above symptoms are present; the recipient twin is edematous and is showing signs of heart failure.Stage V: All of the symptoms above are present and one twin has died.
Treatment
When doctors realize that identical twins share a placenta, the mother will be closely followed for signs of TTTS. Treatment may still be attempted later in the disease, but chances of success are lower.
Fetal Laser Surgery
Laser therapy separates blood vessels in the placenta that allow blood to flow from one twin to the other. The surgery is generally considered more successful than amniotic fluid reduction. Twins born after fetal laser surgery have a higher chance of survival and lower chance of having severe long-term effects of TTTS. The surgery does sometimes fail, however, and TTTS will continue to progress.
Serial Amniotic Fluid Reduction
Amniotic fluid is drained from the sac surrounding the recipient twin. The procedure may be done only once or several times. The theory is that reducing fluid reduces strain on the recipient twin’s heart and reduces the risk of the uterus overstretching, which may cause preterm contractions.
Long-Term Effects of TTTS
Many of the symptoms of mild TTTS, including anemia and polycythemia (a high red blood cell count), can be successfully treated after birth. Because many TTTS twin pregnancies do not go to term, the long-term effects of TTTS are similar to the long-term effects of prematurity. In advanced cases of TTTS, the infants involved may have long-term effects beyond the problems of prematurity. Intraventricular hemorrhage and other brain lesions are more common in TTTS babies, even after laser treatment or amnioreduction. If the disease is untreated and not followed closely, long-term effects may include heart failure and death of one or both twins.
