New fluorescence endoscope for use in twin–twin transfusion syndrome: In vivo visualization of placental blood vessels

Twin–twin transfusion syndrome (TTTS) is a condition in which twins share blood disproportionately by the communicating vessels in the shared placenta, resulting in high fetal and perinatal mortality. Fetoscopic laser photocoagulation is performed to interrupt these communicating vessels; however, small vessels are often missed due to the poor image obtained with a fetoscope. We have developed a fluorescence endoscope capable of visualizing very small vessels, even in amniotic fluid, and we investigated its feasibility for in vivo visualization of placental vessels. Indocyanine green (ICG) was given at single doses of 0.5, 1.0, and 1.5 mg/kg, respectively, into the maternal circulation of pregnant rabbits, and the endoscope was used to identify the placental vessels. The vessels were detected within 15 s after ICG injection for about 10 min. The brightness difference between the intervillous space and the umbilical vessels was significantly smaller after administration of 0.5 mg/kg than after 1.0 mg/kg (p = 0.02) or 1.5 mg/kg (p = 0.01). Even very small vessels (0.2 mm in diameter) were detected. In conclusion, our new endoscope successfully provided a detailed view of the placental vessels in vivo. The results are promising for future TTTS laser surgery.