Twin-to-Twin Transfusion Syndrome (TTTS) is a serious complication affecting identical twins who share a single placenta (monochorionic twinning). The shared placenta contains abnormal vascular connections, or anastomoses, linking the fetuses’ blood circulations. This leads to an unequal exchange of blood: the “donor” twin gives away too much blood, becoming dehydrated and anemic, while the “recipient” receives too much, leading to fluid overload and potential heart failure. Without intervention, the mortality rate for both twins in severe cases often exceeds 90 percent.
Defining the Intervention for TTTS
The definitive intervention for this severe condition is Fetoscopic Laser Photocoagulation (FLP), also known as Selective Fetoscopic Laser Photocoagulation (SFLP). This minimally invasive surgery is performed while the babies are still in the womb and is the standard treatment for severe TTTS. The main objective is to identify and permanently seal the abnormal blood vessel connections on the surface of the shared placenta.
Sealing these connections prevents the unequal shunting of blood between the twins. By coagulating the anastomoses, the surgeon effectively divides the shared placenta into two separate circulatory territories, one for each twin. This halts the progression of the syndrome, allowing both fetuses to develop with independent blood supplies and reducing strain on the recipient twin’s heart.
The Surgical Process Explained
The procedure is typically performed in a dedicated fetal surgery center, often using local anesthesia and conscious sedation for the mother. A small incision is made in the mother’s abdomen, through which a thin metal tube called a trocar is inserted into the uterus and the amniotic sac.
A fetoscope, which is a medical telescope with a camera, is passed through the trocar. This instrument provides the surgeon with a detailed view of the placental surface and the blood vessel connections. The surgeon uses this visualization to map out the abnormal communicating vessels that cross the membrane.
Once the abnormal connections are identified, a laser fiber is guided through the fetoscope to the placenta. Laser energy is used to coagulate, or seal shut, each communicating vessel. After the connections are sealed, some surgeons perform “Solomonization,” drawing a continuous laser line across the entire vascular equator to eliminate unseen connections and ensure circulation separation.
The final step often involves an amnioreduction, draining excessive amniotic fluid accumulated in the recipient twin’s sac. Removing this excess fluid helps reduce the risk of premature labor and rupture of the membranes. The fetoscope and trocar are then removed, and the incision is closed.
Determining Patient Eligibility and Timing
Patient eligibility for FLP is determined by the severity of the disease and the gestational age. The universally accepted tool for assessing severity is the Quintero staging system, which classifies the condition from Stage I (least severe) to Stage V (death of one or both twins). Intervention is typically recommended for patients diagnosed with Stage II, III, or IV TTTS, as these stages indicate worsening disease and significant risk.
Stage I TTTS, where only fluid discordance is present, is often managed with close monitoring, though some cases may qualify for laser treatment if other risk factors exist. The surgery is most effectively performed between 16 and 26 weeks of pregnancy. Treating the condition earlier in the second trimester provides the fetuses with more time to recover and grow, which is important for long-term health.
Contraindications include significant maternal health issues, placental positioning that blocks vessel access, or gestation past 26 weeks. Detailed ultrasounds, including Doppler studies and fetal echocardiograms, are performed to confirm the disease stage and ensure the procedure is the safest course of action.
Post-Surgical Monitoring and Expected Outcomes
Following the procedure, the mother is usually monitored in the hospital for one to two days for signs of premature labor or other complications. Medications are often administered to prevent the onset of contractions. Once discharged, the mother begins frequent follow-up care, including weekly or bi-weekly ultrasounds to monitor the fetal condition.
Regular ultrasounds are essential for checking blood flow through the umbilical cords and fetal blood vessels, tracking growth, and monitoring amniotic fluid levels. The goal of monitoring is to ensure the laser treatment successfully separated the circulations and that the fetuses are recovering independently. Fetal echocardiograms may also be repeated to assess the recipient twin’s heart function, which was strained by fluid overload.
Outcomes after successful FLP are generally positive compared to the nearly universal mortality associated with untreated severe TTTS. Survival of at least one twin is achieved in approximately 85 percent of cases, and both twins survive in 50 to 75 percent of cases. While the procedure significantly improves prognosis, risks remain, including preterm labor, premature rupture of membranes, and potential neurological issues for a small percentage of survivors. FLP is a highly effective method for halting the syndrome’s progression and maximizing the chances for a healthy outcome.