TTTS

Twin-to-Twin Transfusion Syndrome (TTTS) is a prenatal condition affecting identical twins or higher-order multiples who share a placenta (monochorionic pregnancies). TTTS results from an imbalance in the blood flow between the twin fetuses through connecting blood vessels within their shared placenta. This condition can lead to significant morbidity and mortality if not treated promptly.

Causes and Pathophysiology

TTTS occurs due to abnormal connections between the blood vessels in the placenta that supply oxygen and nutrients to the fetuses. In a typical pregnancy, each fetus receives an equal share of resources. However, in TTTS, these connections allow blood to flow unevenly between the twins. One twin, known as the donor, receives less blood and can suffer from malnutrition and dehydration. Conversely, the recipient twin gets too much blood, leading to an overload on the heart and potential heart failure.

Symptoms and Diagnosis

The primary symptom of TTTS is a noticeable difference in amniotic fluid levels between the two amniotic sacs, detectable via ultrasound. The donor twin's sac has decreased fluid (oligohydramnios), while the recipient's has increased fluid (polyhydramnios). Other diagnostic tools include fetal echocardiography to assess the twins' heart functions and Doppler ultrasonography to examine blood flow.

Staging

TTTS is classified into five stages, from I (mild) to V (critical):

• Stage I: Significant difference in amniotic fluid levels but no abnormal blood flow yet.
• Stage II: Abnormal blood flow detected in the umbilical cord or fetal vessels.
• Stage III: Abnormal blood flow in the fetuses' ductus venosus or bladder not visible in the donor twin.
• Stage IV: Ascites or hydrops detectable in either twin.
• Stage V: Demise of one or both twins.

Treatment

The treatment for TTTS depends on the severity of the condition and the gestational age at diagnosis. Options include:

• Amnioreduction: Removal of excess amniotic fluid to reduce the risk of preterm labor and improve the imbalance in blood flow.
• Laser Photocoagulation: A minimally invasive surgery that uses a laser to seal off the abnormal blood vessels in the placenta.
• Selective Fetoscopic Laser Photocoagulation (SFLP): A more precise version of laser therapy that targets only the problematic vessels.
• Septostomy: Creating a small hole in the membrane dividing the amniotic sacs to balance the fluid levels, though less commonly used due to potential complications.

Prognosis

The prognosis for TTTS varies widely and depends on the stage at diagnosis, the timeliness and type of intervention, and the presence of any complications. Early detection and treatment can significantly improve outcomes for both twins.

Prevention

Currently, there are no known methods to prevent TTTS. Regular and thorough prenatal care is crucial for early detection and management of this condition, especially in monochorionic twin pregnancies.