Thames Valley Police have released a CCTV image of a man they want trace in connection with the assault.
The 34-year-old woman was in the Co-op on Water Eaton Road in Bletchley when she was approached by a man who directed racial remarks at her.
He followed her to a car then kicked her to the ground. As a result of the assault the woman lost her baby. The man also hit another man with a bag of ice and a bottle.
The incident happened on Saturday 6 August. Police are appealing for witnesses and are asking if anyone who recognises the man in the CCTV image to contact the Thames Valley Police enquiry centre on 101.