Twin-to-twin transfusion syndrome (TTTS) is a serious complication affecting identical, monochorionic twins who share a single placenta. This condition involves an unequal sharing of blood through connecting vessels on the placenta’s surface, creating an imbalance that endangers both lives. The primary treatment is a specialized, minimally invasive procedure called Fetoscopic Laser Photocoagulation (FLP), often referred to as TTTS surgery. FLP aims to correct the core issue by separating the shared circulation, improving the chances of survival and healthy development for both twins.
Understanding Twin-to-Twin Transfusion Syndrome
Twin-to-twin transfusion syndrome is rooted in the shared placenta, where both twins rely on the same network of blood vessels, called anastomoses. In TTTS, the blood flow across these connections becomes unbalanced, leading to a net transfer of blood from the “donor” twin to the “recipient” twin. This unequal blood exchange creates two distinct and dangerous physiological states.
The donor twin becomes hypovolemic, resulting in low blood volume, poor kidney function, and decreased urine production. This lack of fetal urine causes a dangerously low level of amniotic fluid, known as oligohydramnios. Conversely, the recipient twin becomes hypervolemic, experiencing a blood volume overload that forces the heart to work harder. This overload leads to excessive urine production and an overabundance of amniotic fluid, known as polyhydramnios.
The severity of TTTS is classified using the Quintero Staging System, which helps specialists determine the progression of the disease and the urgency of intervention.
Quintero Staging System
- Stage I: Both oligohydramnios and polyhydramnios are present, but the donor twin’s bladder is still visible on ultrasound.
- Stage II: The donor twin’s bladder is no longer visible, indicating severe hypovolemia.
- Stage III: Abnormal blood flow studies (Doppler findings) are present in either twin, suggesting compromised circulation.
- Stage IV: Characterized by the development of hydrops fetalis—excessive fluid accumulation in the baby’s body—in one or both twins.
- Stage V: The in utero demise of one or both fetuses.
Diagnosis and Criteria for Surgical Intervention
The diagnosis of TTTS relies on detailed prenatal ultrasound and Doppler studies. The defining characteristic is the oligo/polyhydramnios sequence, typically defined as a maximum vertical pocket of amniotic fluid less than 2 centimeters in the donor twin’s sac and greater than 8 centimeters in the recipient twin’s sac. This fluid discordance signals the underlying blood volume imbalance.
To determine the need for surgery, specialists assess the Quintero stage and gestational age. FLP is the preferred treatment for patients diagnosed with Stage II, Stage III, or Stage IV TTTS. The procedure is usually performed between 16 and 26 weeks of gestation, as intervention outside this range presents additional challenges.
Doppler ultrasound assesses blood flow in the umbilical cord and fetal vessels. Abnormal Doppler findings, characteristic of Stage III TTTS, include absent or reversed flow in the umbilical artery or abnormal flow in the ductus venosus. These patterns indicate cardiac strain and circulatory compromise. Their presence suggests a severity that warrants surgical correction to prevent further deterioration.
The Fetoscopic Laser Ablation Procedure
Fetoscopic Laser Photocoagulation (FLP) is a minimally invasive surgical technique targeting the abnormal vascular connections on the shared placenta. The goal is to permanently separate the circulations of the two twins. The procedure is performed while the mother is under local anesthesia and sedation, though an epidural may be used depending on the placenta’s location.
The surgeon makes a small incision (3 to 5 millimeters) in the mother’s abdomen, guided by continuous ultrasound imaging. A thin metal tube, or trocar, is inserted into the recipient twin’s amniotic cavity. Through the trocar, a fetoscope (a small camera) is passed, providing a magnified, direct view of the placental surface on a monitor.
The surgeon systematically examines the placenta to locate all connecting blood vessels (anastomoses) causing the unbalanced blood flow. Once identified, a laser fiber is threaded through the fetoscope. Laser energy is then used to coagulate and seal these vessels shut, effectively halting the harmful blood transfer and separating the two fetal circulations.
Some centers utilize the Solomon technique, where a laser line is drawn on the placental surface between the sealed vessels. This step helps coagulate smaller, unseen connections, ensuring the permanent separation of blood supplies. Once all connections are coagulated, the surgeon performs an amnioreduction, draining the excess amniotic fluid from the recipient twin’s sac through the same sheath.
Post-Procedure Care and Expected Outcomes
Following the procedure, the mother is typically monitored overnight for complications, such as preterm labor or premature rupture of membranes (PPROM). Medications to suppress uterine contractions are often administered immediately after surgery. Due to the minimally invasive nature of FLP, the mother’s recovery time is relatively short, but close monitoring remains necessary for the remainder of the pregnancy.
Specialized ultrasound and fetal echocardiogram follow-up appointments are scheduled weekly to ensure TTTS has resolved and to monitor fetal health. Resolution of the fluid discordance and normalization of Doppler findings are usually observed within the first week. Continued monitoring is necessary to watch for potential long-term issues, such as the recurrence of TTTS or the development of Twin Anemia-Polycythemia Sequence (TAPS).
The prognosis for TTTS is significantly improved with FLP compared to no treatment. With surgery, the chances of at least one twin surviving range from 85% to 90%, and the dual-twin survival rate is approximately 65% to 70%. While a small risk of long-term neurodevelopmental impairment exists, the incidence of cerebral palsy in children who undergo FLP is considerably lower than in those who survive untreated TTTS.