A 5-stage system is used to describe the severity of TTTS. In general, higher stages of TTTS have less favorable outlooks. TTTS can worsen, improve, or stay the same at any stage but is less likely to improve at advanced stages.

TTTS is diagnosed with ultrasound. If you are pregnant with MCDA twins, you will have regular ultrasound exams to check for TTTS starting at around 16 weeks of pregnancy.

Since TTTS can develop at any time during pregnancy, ultrasound screening will continue until delivery.

Management depends on many factors, including gestational age (how far along the pregnancy is) and the TTTS stage. Options may include expectant management, fetal therapy if you are a candidate, amnioreduction in some cases, or termination of one or both twins (abortion). Depending on the geographic location and associated laws, abortion may not be offered. 

You may be referred to a fetal care center for treatment. Fetal care centers provide specialized care for pregnant people with conditions that put them and the fetus(es) at a high risk of complications.  

Fetoscopic laser surgery (FLS) is a type of minimally invasive surgery used to treat TTTS and other complications of twin pregnancies. It is usually offered between 16 and 26 weeks of pregnancy. It can sometimes be considered at earlier or later gestational ages. FLS is best performed at a fetal care center.

InFLS, a fetoscope (a long, specialized camera) is inserted through the mother’s abdomen and into the uterus into the recipient twin’s amniotic sac. A laser is then used to seal off the connections between the twins’ blood vessels. Sealing these connections stops the blood flow between the twins.

FLS is considered the best available treatment for early-onset, advanced-stage TTTS. Overall, when FLS is performed at a fetal care center:

• Both twins survive in 50% to 70% of cases

• 1 twin survives in 20% to 30% of cases, and

• None survive in 10% to 20% of cases.

Although FLS may treat TTTS, it comes with several risks:

• Preterm premature rupture of membranes (PPROM). This is the most common complication of FLS. PPROM can cause serious health problems for a pregnant person, such as infection. For the fetus, PPROM can lead to stillbirth or preterm birth.

• Placental abruption, in which the placenta separates from the wall of the uterus.

• Fetal risks, including injury during the procedure and fetal death.

• Twin anemia-polycythemia sequence (TAPS), another type of unbalanced blood flow that can develop after FLS (discussed below).

Preterm birth is common after FLS. One study found that, on average, people remained pregnant for about 10 more weeks following FLS, with most giving birth around 30 weeks of pregnancy.   

Although most twins born after FLS have normal brain function, up to 1 in 5 have neurologic problems at 2 years of age. These deficits are likely related to being born preterm as well as to the TTTS itself.

In amnioreduction, a thin needle is inserted into the uterus to remove excess amniotic fluid. It is typically done under ultrasound guidance. Amnioreduction may be done when TTS is diagnosed later in pregnancy and fetal therapy is no longer an option.

TAPS occurs when one twin slowly loses blood to the other twin. TAPS causes one twin to have anemia (low red blood cell count) and the other twin to have polycythemia (high red blood cell count). TAPS can occur naturally or as a complication of FLS for TTTS.

The unbalanced blood flow can cause heart and neurological problems for both twins. There is also an increased risk of preterm birth and growth problems. Some twins with TAPS may not survive until birth. However, outcomes vary widely and are hard to predict.

TAPS may be identified during the second or third trimester of pregnancy or after birth. Before birth, Doppler ultrasound may be used to screen for the condition if it is suspected. TAPS often presents with additional ultrasound findings that can confirm the diagnosis.

After birth, TAPS may be suspected when there is a visible physical difference in the twins: one may be pale, and the other may have a ruddy or red-colored skin tone. Blood tests after delivery can confirm a diagnosis of TAPS when there is suspicion that it is present.

Many options can be considered when managing TAPS. Care decisions are often made on a case-by-case basis. Management depends on gestational age, the severity of the condition, technical considerations, and whether other fetal or maternal concerns are present. Close monitoring is usually recommended for mild cases of TAPS diagnosed before 32 to 34 weeks. After 32 to 34 weeks, delivery may be recommended. If TAPS is diagnosed after birth, the baby may need specialized pediatric care.

For more severe cases of TAPS diagnosed in the second or third trimester before 32 weeks, you may be referred to a fetal care center. Potential management options that may be offered include FLS, intrauterine blood transfusion therapy, or delivery. Abortion may be considered in rare cases.  

As with TTTS, newborns who survive TAPS have a similarly increased risk of neurologic problems. They may also have long-term health issues due to being born preterm or from the effects of TAPS on developing organs.