"Pump" twin - normal biometry and morphology. There is a small pericardial effusion but no evidence of cardiomegaly or hydrops.
Acardiac twin - distorted and underdeveloped anatomy, severe hydrops with cystic hygromas. A single umbilical artery with flow towards the fetus.
Single posterior placenta. There is a large artery to artery anastomosis on the superficial aspect of the placenta between the pump and acardiac cord insertions (see the second stack).
The cervix is closed.