Monochorionic twin fetuses with a single placenta have anastomotic vessels joining the twin fetuses. A state in which the balance of blood flow between the twins via these blood vessels is disrupted is known as twin-twin transfusion syndrome (hereinafter referred to as TTTS).

Cases in which TTTS occurs prior to 26 weeks’ gestation are treated with Fetoscopic Laser Photocoagulation of the placenta anastomotic vessels (hereinafter, referred to as laser surgery). Please see the TTTS page for further details.

Laser surgery is applied to TTTS cases prior to 26 weeks’ gestation. Cases that meet the criteria for TTTS but are beyond 26 weeks’ gestation do not undergo laser surgery in Japan. For cases in which laser surgery is not applied, the fetus may be delivered early and neonatal management implemented, or treatment such as amniotic fluid removal may be implemented in order to extend the period of pregnancy. Since the onset of TTTS beyond 26 weeks’ gestation has a worse prognosis than usual, however, the opinion has been expressed that it would be preferable to be able to improve the condition of the fetus while still inside the mother, by implementing laser therapy.

Laser surgery is implemented with regard to TTTS between 26 and 29 weeks’ gestation in Europe, and reports suggest it is as effective as when used prior to 26 weeks. For this reason, we in Japan are now implementing a clinical trial involving using the therapy on patients with TTTS at between 26 and 27 weeks (under 28 weeks), and considering its effectiveness and safety.