Twin-twin transfusion syndrome (TTTS) is a condition in which the blood flows unequally between twins that share a placenta (monochorionic twins).
TTTS occurs in 10 to 15 percent of monochorionic twins, and can be very serious if not treated.
There are no known genetic causes of TTTS. Abnormal blood vessel connections cause the fetuses to share blood supply, and one twin (called the donor twin) pumps blood to the other twin (called the recipient). This causes the recipient twin to receive too much blood and the donor twin to receive too little. The increased blood volume causes the recipient twin to produce more than the usual amount of urine, which can enlarge the bladder, producing too much amniotic fluid, and may then lead to heart failure. The donor twin, who receives too little blood, produces less than the usual amount of urine, resulting in a small or absent bladder.
Determining whether the twins share a single placenta is the most important step in evaluating a twin pregnancy for twin-twin transfusion syndrome. An ultrasound examination early in pregnancy (during the first trimester) can best make this distinction. Your doctors will be able to evaluate the severity of TTTS through assessing the amount of amniotic fluid in both sacs, filling of bladder of the donor twin and testing blood flow through various blood vessels in both fetuses. Other tests, including fetal echocardiogram and amniocentesis may be needed.
In TTTS, there is a characteristic series of changes that happens in the recipient twin due to the extra blood coming from the donor twin.
Stage 1 - Polyhydramnios (too much amniotic fluid) in the recipient sac, oligohydramnios (little or no amniotic fluid) in the donor sac
Stage 2 -Donor bladder is not filling and emptying
Stage 3 - Abnormal blood flow patterns, including:
- Absent/reversed umbilical artery end-diastolic velocity (UAEDV)
- Reverse flow in ductus venosus (DV)
Stage 4 - Hydrops, or massive fluid retention that puts both mother and twins at risk
Stage 5 - Death of one or both twins while still in the uterus
Without intervention, TTTS can be fatal for both twins. The treatment depends on the severity of the problem, and may include any of the following:
- Expectant management – Close monitoring with periodic ultrasounds is the best way to evaluate the condition of both twins when surgery is not yet indicated.
- Fetoscopic selective laser photocoagulation – A minimally invasive procedure that stops the sharing of blood from the donor to the recipient, with the goal of halting the progression of TTTS. Depending on the stage of TTTS, this is usually the preferred treatment.
- Amnioreduction – Is a temporary treatment that removes excess amniotic fluid from the recipient twin. This procedure may need to be repeated, but helps to ease any pain or discomfort experienced by the mother due to fluid buildup.
- Selective reduction – Is a last resort. And is only considered when the disease is very advanced and there is a chance the at-risk twin will not survive. This minimally invasive surgery stops the blood flow from the donor twin in order to maximize the outcome for the other twin.