A placenta from a premature baby boy was found discarded in woodland by a dog walker is "definitely human", a police investigation has found.
The remains were found in South Woodchester, near Stroud in Gloucestershire, when a woman walking her dog saw the animal nosing around a plastic bag, containing the placenta, a bowl and medical equipment.
Police said they were very concerned for the mother and for the newborn, who they believe would be around 17 weeks premature.
Detective Inspector Steve Bean, of Gloucestershire Police, said: "Although we were always relatively certain the placenta was from a human, it was not until it was tested in a laboratory that we could be sure.
"The testing has now been carried out and we can say for certain that it was from a human birth. We have also had it confirmed, through DNA testing, that the placenta would be from the birth of a baby boy.
"We are continuing to investigate this discovery, and as yet have not been able to trace the mother, which has been our focus throughout.
"We would still like to hear from anyone with information about who left these items. All calls will be dealt with sensitively."
Inquiries have also been made with local maternity units, however none has admitted a woman who has given birth to a baby of that age, police said.
Anyone with information is asked to ring 101 quoting incident number 433 of July 26.