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Complex Monochorionic Twins

The Stanford Children’s Health Fetal and Pregnancy Health Program specializes in treating complex monochorionic twins. Our program’s maternal-fetal medicine, pediatric cardiology, neonatology, and pediatric surgery specialists provide comprehensive evaluation of and consultation on complex monochorionic twin and triplet gestations, usually in a single appointment.

We provide fetal surgery, including operative fetoscopy, laser coagulation of shared placental anastomoses, amnioreduction, and radiofrequency ablation (RFA), in selected cases.

We have extensive experience in managing twin-twin transfusion syndrome (TTTS), twin anemia-polycythemia sequence (TAPS), twin reverse arterial perfusion (TRAP) sequence, twins with selective intrauterine growth restriction (sIUGR), monoamniotic twins, triplets, and multiple gestations with fetal anomalies affecting one or more fetuses.

What are monochorionic twins?

In most twins, each fetus has its own placenta (dichorionic placentation). Monochorionic twins, twins sharing a single placenta, develop when a single embryo splits early in gestation. With monochorionic placentation, blood vessels cross from one twin sac (amnion) to the other twin sac along the placental surface. These vascular connections (anastomoses) allow for balanced flow between one twin and the other.

In about 15% of monochorionic twin pregnancies, there is increased flow from one twin to the other twin via these anastomoses, resulting in twin-to-twin transfusion syndrome.

Monochorionic Twins Illustration

How is twin-to-twin transfusion syndrome (TTTS) diagnosed?

Unequal blood flow between the twins along the vascular anastomoses of the placental surface can be detected by a dedicated ultrasound exam. Specifically, an assessment of the size of the twins, the amniotic fluid level, fetal bladder size, assessment of the umbilical cord blood flow, and a cardiac evaluation can identify how severe the condition is.

Stages of twin-twin transfusion syndrome:

Stage 1—Polyhydramnios (extra fluid) in the recipient twin sac and oligohydramnios (decreased fluid) in the donor twin sac.

Stage 2—Decreased bladder size in the donor twin.

Stage 3—Vascular or cardiac abnormalities in either the donor or recipient twin. This is assessed using ultrasound Doppler and fetal echocardiogram.

Stage 4—Fetal hydrops: evidence of heart failure in either twin that causes fluid to accumulate in different body parts.

Stage 5—Fetal demise.

What problems can twin-twin transfusion syndrome (TTTS) cause after birth?

The long-term outlook for babies with TTTS depends on how soon the condition is treated and the age of the babies when they are born. Potential health issues include heart and neurodevelopmental conditions.

How does the Packard Children’s Hospital team typically care for monochorionic twins?

Routine ultrasound surveillance for monochorionic twins begins at 16 weeks’ gestation and occurs every two weeks.

We provide comprehensive diagnostic and therapeutic options, including fetoscopic laser coagulation of shared placental anastomoses, amnioreduction (after 26 weeks’ gestation), or selective reduction using radiofrequency ablation or laser. We offer virtual reality educational tools to help you learn about twin-to-twin transfusion syndrome and how we can treat it using innovative surgical techniques.

What does the fetoscopic laser ablation treatment for twin-twin transfusion syndrome (TTTS) consist of?

Fetoscopic laser ablation in complicated cases of TTTS can correct the blood-sharing imbalance caused by TTTS. 

  • During the surgery, a small camera called a fetoscope is inserted into the uterus under ultrasound guidance.
  • This enables doctors to closely examine the placenta and to find the vascular connections between the twins.
  • A laser fiber is then inserted via the working channel of the fetoscope, and under direct visualization the vascular connections can be ablated, thereby stopping the blood flow from one twin to the other.
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