Fetoscopic demonstration of feto-fetal hemorrhage before actual demise of a monochorionic twin, successful antenatal treatment, and narrative review of the literature.

Feto-fetal hemorrhage (FFH) through placental vascular anastomoses is believed to be responsible for the death or damage of a "second twin" after the demise of a "first twin (co-twin)" in monochorionic twin pregnancies. However, the timing of FFH has been difficult to determine. The resulting anemia in the surviving twin can be suspected by the finding of an elevated middle cerebral artery peak-systolic velocity (MCA-PSV), but this elevation may lag for at least 4 h after the demise of the first twin. Knowledge of the timing of FFH may have important clinical implications, as it may dictate if and when attempts to prevent death or damage to the second twin by delivery or intrauterine fetal transfusion would be warranted. We present a case that supports the notion that FFH occurs before the actual demise of the first twin. A review of the literature was also conducted.