A rare condition that only happens among identical twins while they are developing inside their mother's womb is known as the Twin-to-Twin Transfusion Syndrome (TTTS). TTTS is a complication of disproportionate blood supply, wherein the blood of one twin moves or transfuses to the other twin. This may result to a problem for both infants depending on the severity of the transfusion. The condition is also known as Feto-Fetal Transfusion Syndrome (FFTS) and Twin Oligohydramnios-Polyhydramnios Sequence (TOPS).
TTTS is not hereditary or genetic. It can affect any developing identical twins who share a common monochorionic placenta. Events that may lead to TTTS are:
- timing of the twinning event
- number and type of connecting vessels
- the way the placenta is shared by the twins
Because the twins share a single placenta, their blood supplies can become connected which means that they share blood circulation. Normally, each fetus will use its own portion of the placenta but the connecting blood vessels within the placenta will allow blood to pass from one twin to the other. The disproportionate transfusion of blood from one twin to the other can happen depending on the number, type and direction of the interconnecting blood vessels.
The twin who loses the blood is called the donor while the other who gets the blood is the recipient. The donor, whose blood volume will decrease, may suffer from a retarded growth and development and decreased urinary output which can lead to oligohydramnios or abnormal level of amniotic fluid. The increase in blood volume will also not be good for the recipient twin because it can cause a heart failure as a result of the strain of the baby's heart. It can also lead to a higher urinary output resulting in excessive amniotic fluid and polyhydramnios.
The TTTS' severity is classified into five stages. Stage I is characterized by the presence of a small amount of amniotic fluid (oligohydramnios) around the donor twin and a large amount of amniotic fluid (polyhydramnios) around the recipient twin. In stage II, aside from the signs in the first stage, the ultrasound is not able to identify the bladder in the donor twin. All these plus an abnormal blood flow in the umbilical cords characterizes stage III. In stage IV, there is swelling under the skin of the recipient twin and he or she appears to be having fetal hydrops or heart failure, plus all those stage III characteristics. All these will be present in stage V, plus one of the twins has died. Usually, it is the donor but it can also happen to the recipient.
TTTS can lead to severe disabilities or even death if it happens before the 26 weeks of pregnancy. If the twins develop the condition after 26 weeks of gestation, they have a greater chance of being born alive and not suffering from disabilities. Usually the donor twin will be born smaller, pale, anemic and dehydrated while the recipient twin will be born larger, with redness, too much blood, have increased blood pressure and in danger of developing cardiac failure.
An ultrasound can usually diagnose this condition during pregnancy. Treatment during pregnancy may include several amniocentesis or a fetal laser surgery to interrupt the blood flow from one twin to the other. Treatment after birth will depend on the babies' specific symptoms.