A baby declared stillborn at the John Radcliffe was rejected by a mortuary because she was in fact still alive.
Emma Cox was 17 when she gave birth to twins in 2011 after losing a third baby early in pregnancy.
When she went into labour at 24 weeks, one baby - Hope - was resuscitated and taken to the neonatal unit.
The other, Lilly, was declared stillborn, but couldn't be accepted by the mortuary because she was later found to be alive.
The shocking allegation has been uncovered in a joint investigation into the Oxford University Hospitals Trust's maternity and neonatal unit by the New Statesman and Channel 4 News.
The investigation has heard from more than 20 families who say they have lost babies, had children born with severe disabilities, or suffered serious harm themselves, as a result of poor care at the trust.
Ms Cox said: “At 24 weeks I went into spontaneous labour. They were born. I was told that one of them was stillborn and the other one was taken and resuscitated and taken to the neonatal unit.
"A short time later Lilly was brought back to me and they said the mortuary was unable to take her because she was actually alive."
Ms Cox was denied access to the neonatal unit and said she begged for Lilly to be treated, but doctors refused, she claimed, saying it was to late to intervene.
She and her family tried to keep Lilly alive on a radiator at the John Radcliffe for 12 hours.
Both babies died. Emma’s medical notes, obtained 14 years later, reveal a doctor wrote: "I have encouraged the parents and grandparents to keep the little girl with them, and warned them she may live for many hours.”
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In September, the government announced an investigation into the Oxford Hospitals Trust's maternity and neonatal services.
Health secretary Wes Streeting told the joint investigation that the revelations were "scandalous" and pointed to a "moral failure" in the system.
He has ordered NHS England to investigate the allegations of failings contained in the reporting.
Simon Crowther, interim chief executive at Oxford University Hospitals Trust, said the trust sends its "heartfelt apologies to any family who have not received the standard of care they deserve and our condolences to those who tragically have experienced loss".
He added: "We work hard to listen with care and compassion to the concerns that have been raised, and we remain fully committed to learning from them.
"The trust is participating openly and transparently in the National Maternity and Neonatal Investigation led by Baroness Amos, and we welcome this opportunity to reflect, improve and ensure that every voice is heard."
He added: "However, we recognise that there is much more to do and we remain resolute in our determination to go further."
The trust would not comment on individual cases.
