The collision happened between a BMW and a Toyota on Cooks Lane in Solihull in 2022.
Officers released an image of a man they would like to speak to in connection with the incident. They believe he may have been the driver of the BMW.
They have also arrested an 18-year-old man from the BMW on suspicion of theft of motor vehicle and he has been released on police bail while enquiries continue.
The woman and her family have agreed to release this private and sensitive information to show the impact the collision has had on their lives.
Detective Constable Rachael Johnson, from Force CID, said: "This has had a lasting impact on the family who were left devastated that day at the loss of their unborn baby.
"We have carried out CCTV enquiries and spoken to witnesses and our investigation continues.
"I would appeal directly to the suspect to do the right thing and get in touch with us. Anyone who has any information on his whereabouts or about the incident please get in touch."
Anyone with any information is being encouraged to contact Live Chat on the police website or by calling 101 quoting investigation number 20/471463/22.