Rationale: Monochorionic twins share one placenta and are connected to each other via vascular anastomoses at the placental surface, allowing the blood to transfer bi-directionally between the two fetuses. Unbalanced inter-twin blood transfusion can result in twin anemia-polycythemia sequence (TAPS). Management options include: fetoscopic laser surgery, intrauterine blood transfusion (IUT) with or without partial exchange transfusion (PET), preterm delivery, selective feticide and expectant management. The optimal treatment for TAPS is not clear. Fetoscopic laser surgery is the only causative treatment option, but data on the feasibility of this procedure are mainly based on case reports and small cohort studies. A large randomized controlled trial is needed to evaluate the possible beneficial effect of fetoscopic laser surgery and to determine the optimal treatment option for TAPS.

Objective: The aim of this trial is to investigate whether fetoscopic laser surgery improves the outcome for TAPS twins as compared to the control group (standard care consisting of expectant management, IUT, preterm delivery). The hypothesis is that fetoscopic laser therapy will improve neonatal outcome by prolonging pregnancy.

Study design: International multi-centered open-label randomized controlled trial to assess whether fetoscopic laser surgery (experimental group) improves the outcome of TAPS twins compared to standard care (control group).

Study population: Monochorionic twin pregnancies with TAPS stage 2 (spontaneous or post-laser) diagnosed between 20 and 28 weeks of gestation.

Intervention: In the experimental group fetoscopic laser surgery is performed, whereas the control group is treated with standard care (expectant management, IUT (with PET), selective feticide and/or preterm delivery, depending on the opinion of the fetal surgeon).

Main study endpoints: The primary outcome is gestational age at birth. Secondary outcomes include: perinatal mortality or severe neonatal morbidity, hematological complication, procedure related complications and long-term neurodevelopmental outcome at 2 years.