The 37-year-old was arrested after the stabbing in Croydon which left the woman, aged 26, dead and her baby in critical condition.
The Metropolitan Police said: “Police were called by London Ambulance Service (LAS) at 3.30am on Saturday June 29 to reports of a woman in cardiac arrest inside an address at Raymead Ave, Thornton Heath.
“Officers attended along with the LAS and found the woman, aged 26, suffering from stab injuries.
“It was also established that she was approximately eight months pregnant. Despite the efforts of paramedics, the victim sadly died at the scene.
“Her baby was delivered at the scene before being taken to hospital. The child (we are not confirming gender at this stage) remains there in a critical condition.”
The force said the woman’s next-of-kin have been informed, and that at this early stage, officers retain an open mind as to any motive.
Detective Chief Inspector Mick Norman, who is leading the investigation, said: “This is a horrific incident in which a young mother has lost her life and her child is critically ill.
“Our sympathies go out to her devastated family; they are being supported by specially trained officers following this awful event, and I would ask that they are left alone at this time as they come to terms with the enormity of what has happened.
“A large crime scene is in place, and is likely to be in place for some time. Residents should be aware that if they have any concerns, or information they would like to share with us, that they can speak to any of the officers there, or call our incident room on 020 8721 4005. Alternatively please use the anonymous methods of reporting information to the police, such as Crimestoppers, if you wish.
“At the forefront of our enquiries is understanding what exactly has lead to these tragic circumstances, and we are doing everything we can to establish the facts.”
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