144 hour Visa qualification

Hi, i'm traveling to Shanghai fron Frankfurt via Doha (FRA-DOH-PVG). I will stay 4 days and then continue to Miami, again via Doha (PVG-DOH-MIA). Do I qualify for the 144s free transit or is my trip considered a roundtrip from Doha to Shanghai (DOH-PVG-DOH)?

Thanks!