Alisha Khan, who is 36 weeks pregnant, was taken to Royal Manchester Children’s Hospital after she fainted while she was out shopping.
The 19-year-old girl then left the hospital without treatment and was last seen at around 12.20am on Saturday.
Police said she has not been seen or heard from since - and a spokesman confirmed today that she remained missing.
Detective Sgt Simon Halliwell said: “She left the hospital without treatment or checks and we are concerned she may have an ongoing condition that could harm her or the baby.
“We’d like Alisha to contact us to let us know she is ok.”
“She left the hospital without treatment or checks and we are concerned she may have an ongoing condition that could harm her or the baby"
Alisha is described as mixed race and slim, with brown eyes.
She usually has long dark hair, but is believed to currently have blonde hair tied back into a ponytail.
She was last seen wearing all black clothing, but is known to have a grey jacket and jeans with her.
Anyone with information is urged to contact police on 101.