Twin-to-Twin Transfusion Syndrome (TTTS)
Twin-to-Twin Transfusion Syndrome (TTTS) is a serious complication that can occur in twin pregnancies sharing a placenta. Specialized fetal medicine ultrasound surveillance can help detect TTTS early and assess the condition of both babies, allowing timely counselling and management when required.
Twin-to-Twin Transfusion Syndrome, commonly called TTTS, is a pregnancy complication that occurs mainly in monochorionic twin pregnancies, where both babies share a single placenta. Abnormal connections between the blood vessels of the shared placenta can result in an unequal exchange of blood between the twins.
TTTS occurs in twin pregnancies where the babies share a placenta. It is particularly important to identify chorionicity early in pregnancy because monochorionic twins require closer ultrasound surveillance than twins with separate placentas.
Determining whether twins share a placenta is an important part of the first-trimester ultrasound assessment. Monochorionic twin pregnancies require specialized monitoring because complications such as TTTS, selective fetal growth restriction and Twin Anemia-Polycythemia Sequence can occur.
In a shared placenta, blood vessels from one baby's circulation can communicate with vessels belonging to the other baby. In TTTS, the blood flow through these placental connections becomes unbalanced. One baby becomes the donor twin, while the other becomes the recipient twin.
The donor twin may receive less effective blood flow and may produce less urine, leading to reduced amniotic fluid. The recipient twin may receive an excessive amount of blood, resulting in increased urine production and excess amniotic fluid. The degree of these changes can vary between pregnancies.
TTTS is primarily diagnosed and monitored using ultrasound rather than maternal symptoms alone. Important ultrasound findings include unequal amniotic fluid levels, changes in fetal bladder filling and abnormalities in fetal blood flow. Maternal symptoms can occur when there is significant excess amniotic fluid, but a mother may have no obvious symptoms even when TTTS is developing.
A characteristic feature of TTTS is a difference in the amount of amniotic fluid surrounding the two babies. The donor twin may develop oligohydramnios, while the recipient twin may develop polyhydramnios. Measuring the deepest vertical pocket of fluid around each fetus is an important part of ultrasound surveillance.
Assessment of the fetal bladder is another important component of TTTS surveillance. In more advanced disease, the bladder of the donor twin may become difficult or impossible to visualize because of reduced urine production. Bladder filling is therefore assessed carefully during serial ultrasound examinations.
Doppler ultrasound can provide additional information about blood flow in the umbilical arteries and other fetal vessels. Doppler assessment helps the fetal medicine specialist evaluate the condition of both babies and identify signs that may indicate increasing disease severity.
Current fetal medicine guidance recommends starting ultrasound surveillance for TTTS at around 16 weeks in monochorionic-diamniotic twin pregnancies and repeating examinations at least every two weeks. More frequent assessment may be recommended when there are concerning findings or clinical concerns.
TTTS is commonly classified using the Quintero staging system. The system describes increasing severity based on ultrasound findings, including amniotic fluid imbalance, fetal bladder visibility, abnormal Doppler findings, hydrops and fetal demise. Staging helps specialists communicate the severity of TTTS and plan appropriate management.
Stage I is characterized by the typical polyhydramnios-oligohydramnios sequence, while the donor twin's bladder remains visible. Some Stage I pregnancies remain stable, while others can progress. Close fetal medicine surveillance is therefore important.
In Stage II, the donor twin's bladder is not visible during the ultrasound examination. This finding indicates more significant reduction in urine production and requires specialist assessment and close monitoring.
Stage III is associated with significant abnormal Doppler blood-flow findings in one or both fetuses. These changes may indicate cardiovascular or circulatory compromise and require urgent specialist evaluation.
Stage IV involves hydrops, which means abnormal accumulation of fluid in one or both fetuses. This represents severe fetal compromise and requires management in a specialist fetal medicine or fetal therapy setting.
Stage V refers to fetal demise of one or both twins. When a single fetal demise occurs in a monochorionic pregnancy, the surviving twin requires careful specialist assessment because the shared placental circulation can create additional risks.
Regular ultrasound surveillance is important because TTTS can develop and progress over a relatively short period. Monitoring amniotic fluid, fetal bladder filling, fetal growth and Doppler blood flow helps identify changes that may require closer observation or treatment.
Fetoscopic laser photocoagulation is an established treatment for significant TTTS. During the procedure, a fetal therapy specialist uses a fetoscope to identify abnormal communicating blood vessels on the shared placenta and uses laser energy to close the relevant vascular connections.
For TTTS diagnosed between approximately 16 and 26 weeks, fetoscopic laser surgery is the standard treatment for Stage II through Stage IV disease according to current specialist guidance. Management of Stage I disease is individualized and may involve close surveillance or consideration of laser therapy depending on the clinical situation.
After fetoscopic laser treatment, the pregnancy requires continued specialized ultrasound surveillance. Follow-up examinations assess amniotic fluid, fetal growth, Doppler blood flow, fetal cardiac function and possible complications such as recurrent TTTS, Twin Anemia-Polycythemia Sequence or fetal growth restriction.
Twin Anemia-Polycythemia Sequence, or TAPS, is another complication of monochorionic twin pregnancy. Unlike typical TTTS, TAPS is characterized mainly by a difference in fetal blood hemoglobin levels and may occur without major differences in amniotic fluid. Middle cerebral artery Doppler assessment can help identify this condition.
Growth differences can occur in monochorionic twin pregnancies and may coexist with TTTS or other placental complications. Serial ultrasound measurements of fetal growth and Doppler blood flow help monitor the wellbeing of both babies.
Monochorionic twin pregnancies benefit from structured fetal medicine surveillance. Regular assessment allows changes in fluid levels, bladder filling, fetal growth and Doppler blood flow to be identified as early as possible and helps determine when additional specialist care may be required.
At Promise Fetal Medicine & Pregnancy Scan Centre in Jalandhar, monochorionic twin pregnancies can be assessed with specialized ultrasound monitoring focused on chorionicity, amniotic fluid, fetal bladder filling, fetal growth and Doppler blood flow. When findings suggest TTTS, appropriate fetal medicine counselling and referral for specialist fetal therapy can be discussed.
If you are carrying twins who share a placenta, regular fetal medicine ultrasound monitoring is important. If an ultrasound report mentions TTTS, unequal amniotic fluid, an absent fetal bladder or abnormal Doppler findings, a timely consultation with a fetal medicine specialist can help assess the pregnancy and discuss the appropriate next steps.
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Twin-to-Twin Transfusion Syndrome (TTTS) is a serious complication that can occur in monochorionic twin pregnancies, where twins share a single placenta. In TTTS, abnormal connections between the twins’ blood vessels can cause an unequal distribution of blood flow. One twin, known as the donor twin, may receive less blood, while the recipient twin receives an excessive amount. This can affect the growth, amniotic fluid levels, bladder function, and heart function of one or both babies. At Promise Fetal Medicine & Pregnancy Scan Centre in Jalandhar, regular ultrasound and Doppler assessments can help monitor monochorionic twin pregnancies and identify signs of TTTS early. Timely specialist evaluation is important because treatment options depend on the severity and stage of the condition.
Director and Chief Fetal Medicine Specialist
Baby's Journey Through Pregnancy
