Anyone had blood tests to discover babys blood group?

Mary • Mum of 4 expecting our 5th exciting!
Im r neg blood type and usually get offered anti bodies injection at 28wks preg incase babys blood isnt compatible with mine. However i dont want to take the shot if not needed! I read a simple blood test can detect the babys blood dna so we know if baby is same as me or not. Anyone else know anything?