The family of Sophie Burgess are pursuing a negligence case against the Royal Wolverhampton Hospital NHS Trust after she died at New Cross Hospital four years ago.
The trust said a three-hour delay in transferring the 19-year-old, from Telford, to intensive care and failure to provide the correct management to treat her deteriorating condition contributed to her death.
It said lessons had been learned and it was helping to improve treatment.
Sophie’s mother, Mandy Burgess, said they wanted people to know the truth.
“A lot of people assume that Sophie died in childbirth but we want people to know that she didn’t - she died because mistakes were made in that hospital,” she said.
"I am still very bitter. Sophie wouldn’t have given up without a fight but they never gave her that chance. They took it away from her.
"She was young and healthy and would have survived.
“You feel like you have let your kids down. It’s hell.
"I knew I should never have left her on her own in that hospital the night she died. The guilt will be there for the rest of my life.”
Law firm Lanyon Bowdler is handling the case for the family.
Kay Kelly, head of clinical negligence, said: "“The family are still completely devastated by the tragedy which occurred on March 13, 2015.
“Sophie Burgess was a happy and healthy 19-year-old who was excitedly looking forward to being the mother of twins, but she never got to meet her babies due to failings in her care.
"The NHS Trust has accepted opportunities were missed to provide Sophie with the urgent specialist treatment she needed.
"The three-hour delay in transferring her to intensive care was due to a lack of leadership and management of the two conditions which led to her death - sepsis and HELLP Syndrome.
"Sophie’s family are understandably very angry and have pursued a clinical negligence case against the NHS Trust on behalf of Sophie’s infant twins, and now want to raise awareness to help other families avoid having to go through the same nightmare.
"They have been incredibly brave and strong throughout a terrible ordeal which no family should have had to face, and I am glad we have managed to prove the case.”
A spokeswoman for the Royal Wolverhampton Hospital NHS Trust, said: "The trust would once again like to offer our condolences and regret for the circumstances which led to the death of Sophie following the birth of the twins.
"The lessons identified from our investigation have been shared within the Trust and continue to help us to identify and manage sepsis as early as possible."
'We don't want this to happen again'
Sophie’s family say they are still trying to get to terms with her death.
“It happened four years ago but life isn’t getting any easier, it’s getting harder,” Mandy said.
“The twins are four now and starting to understand that they don’t have a mom.
“Mother’s Day was just so hard. We went to Sophie’s grave, which we call Sophie’s garden, and tried to explain to them why their mom isn’t here anymore. It’s just heartbreaking.
“The twins are being brought up by their dad, who has done really well, and we all help as much as we can but it’s just incredibly hard and we are all exhausted.”
Sophie’s brother, Craig Burgess, said the family was now campaigning to raise awareness of Sepsis and HELLP Syndrome, a variant of pre-eclampsia, which is a little-known but life-threatening pregnancy complication.
“Life has been so hard for everyone, especially the twins, since it happened,” he said.
“There is always something to remind us of Sophie, like Mother’s Day, and the twins’ birthday is always going to be the same day that we lost Sophie which is just absolutely heartbreaking,” he said.
“There has been no closure whatsoever and we are hoping that the legal case coming to an end will help with that. We also hope telling Sophie’s story will help in some way.
“We want to raise awareness of Sepsis and HELLP Syndrome, because many people don’t realise how dangerous they are – especially HELLP Syndrome. We had certainly never heard of it before.
“”If we can help to save one person’s life by sharing Sophie’s story then we would be happy with that.
“The hospital wrote to us to apologise but I haven’t been able to bring myself to read it properly.
“They can apologise all they want but they won’t be able to bring Sophie back.”