The teenager rang police on Wednesday evening following public appeals to say she was the mother of the child found at the Bell Waste Control centre in Scunthorpe.
She was admitted to Scunthorpe hospital for post natal care.
Investigations continued at Bell Waste throughout the day and a post mortem examination was being carried out yesterday afternoon.
A spokeswoman for Humberside Police said that the teenager, who lives locally, was in a distressed state when she called.
The spokeswoman went on: “Police officers went to meet her and she was taken to Scunthorpe General Hospital where she has been admitted for appropriate post natal care.
“Whilst it is not yet clear exactly what the circumstances of this incident are, it is believed that the baby was newborn.
“The teenage girl is now receiving the necessary care she requires and further inquiries into the circumstances of what happened will be made in due course.”
The baby was found on a belt where cardboard, wood, metal and paper and other objects are separated for recycling.
At first the worker who found the child thought it was a doll, but quickly realised the truth.
He has been given time off work to recover.
The firm has been checking through its records to assist the police investigation.