A pregnant woman stole another woman's identity to try to stop her own baby from being removed from her care.
The woman, who has not been identified, pretended to be Kay Costin when she gave birth at Walsall Manor Hospital in August and was then able to leave with the child.
A leaked document from the hospital said the identity details were taken from a social-networking site.
But Mrs Costin has denied making her personal details publicly available.
Walsall Manor Hospital said such cases were "very rare".
Mrs Costin, who was also pregnant, had been booked in to give birth at Birmingham City Hospital.
The woman who stole her identity has since had her own baby taken away.
The incident only came to light when Mrs Costin attended a GP appointment while she was still pregnant.
However, her GP had notes to show she had given birth on 31 August.
Mrs Costin told the BBC the only information that she had made public on social media was her name.
"No address, no date of birth, no doctors, it's all private," she said.
"I think she knows me, I think it was someone I was friends with, but we haven't been told who it is," Mrs Costin said.
The document obtained by the BBC shows the woman who stole the identity referred herself to Walsall Healthcare NHS Trust while in labour.
Police said a 24-year-old woman had been questioned in September, but no charges were pursued.
The woman had previously had three children removed from her, all of whom were placed in the care of the local authority.
The health trust said the woman had provided details of her assumed identity but did not have her pregnancy records with her.
Instead, she said the notes were with the community midwife.
The hospital midwife in Walsall called the neighbouring hospital to confirm the pregnancy details of Mrs Costin, who the woman in labour claimed she was.
Mrs Costin said she would like an apology from the hospital for the "distress" she went through, which she believes caused her to need an emergency caesarean.
The Walsall Healthcare Trust said it had carried out an investigation into what happened.
It said it had now strengthened its procedures for admitting women in labour and had reassessed how it then discharged them and their babies.
The trust said anyone turning up without their notes would need to have their identification formally confirmed by the hospital, social services and the police.
Anyone who cannot get their identity confirmed may be prevented from being discharged from the hospital.
Richard Kirby, the trust's chief executive, said: "The incident related to an identity theft by an individual using our maternity service. Although this is a very rare occurrence, the learning from this incident has been of value across the organisation."
Kat Tremlett from the UK Safer Internet Centre, said: "Pregnant women and new mums often use online forums to share experiences.
"You are talking to people you believe are going through the same experiences and perhaps you let down your guard a little.
"We would urge women to take the same precautions they would use on any other internet site."
Jo Walker, from the Suzy Lamplugh Trust, which campaigns on the subject of personal safety, said: "It's easy to think you know people you have met online and that they are your friends and and you can end up sharing a lot of information with them.
"But you have no idea if what they are saying is true and how they are going to use that information."