A health worker has been arrested on suspicion of poisoning an infant who died at a children's hospital.
West Midlands Police said the woman, 27, was arrested last Thursday, hours after the death, on suspicion of administering poison with intent to endanger life.
She has since been released by officers, while they wait for the results of forensic tests.
Police said in a statement: "We've arrested a 27-year-old woman in connection with the death of an infant.
"The child sadly passed away on Thursday at hospital.
"The woman was arrested on Thursday evening at a property in the West Midlands area on suspicion of administering poison with intent to endanger life.
"She has been released while the investigation continues and the results of forensic tests are examined.
"The family of the child are being supported by specially-trained officers."
A spokesperson for Birmingham Women's and Children's NHS Foundation Trust said: "Following the death of an infant at our Paediatric Intensive Care Unit at Birmingham Children's Hospital, we have asked West Midlands Police to examine what has happened, in line with our own safeguarding policy.
"The staff member involved has been suspended by the Trust after following the national process on the sudden unexpected death of a child.
"We are supporting the infant's family at this distressing time and ask that privacy is respected during this process."
Birmingham Children's Hospital is a leading centre for specialist paediatric care.
It treats children and young people up to 16-years-old.