The naked body of a baby girl, who detectives called Pearl, was found on 4 April by a dog walker in Roch Valley Woods in Heywood, Greater Manchester.
Police have now arrested a 48-year-old man and a 33-year-old woman on suspicion of murder, concealing a birth and preventing a lawful burial.
According to the Press Association, the pair are believed to be related to the child.
Forensic examinations revealed the baby was born with a congenital heart defect, meaning two of her ribs were missing.
Further inquiries have including DNA testing to work out what happened to baby Pearl. Police previously said they believed the girl to be white, but possibly with some mixed race heritage.
Pearl was found at about 7.10am in the Bluebell Woods on 4 April, unclothed, without a blanket or nappy.
Detective Superintendent Lewis Hughes, who headed up the Major Incident Team investigation, said: “This continues to be an incredibly heart-breaking case for everyone involved – from the detectives working painstaking hours to find those responsible to members of the public that have felt the loss of Pearl.
“While we have two people in custody, our investigation is still very much ongoing and I would continue to urge anyone with even the smallest piece of information – no matter how insignificant it may seem – to please get in touch.
“We’re committed to finding the truth for this little girl and truly believe the public could hold the key to this tragic case.”
Detectives have taken on a behavioural psychologist as part of the investigation.