A mother lost her unborn twins after she was sent home from hospital and told her pain was a strained muscle.
Mother-of-three Nicola Jaffray, 32, from Middlesbrough, had gone to James Cook University Hospital complaining of pain in her ribs.
But despite having contracted the serious condition twin-to-twin transfusion syndrome, she was sent home by staff who told her she had pulled a muscle.
Days later she lost both her babies after she was rushed back into hospital by ambulance and the diagnosis was made too late.
Her partner David Bielicki, 36, said: "It has been a living nightmare.
"To be told and assured by a midwife that your babies are perfectly fine and then days later you are cradling them - lifeless, well it is devastating and hard to get your head around."
As a result, South Tees Hospitals NHS Foundation Trust apologised to the couple, saying an ultrasound scan should have been performed when she first told them about the pain.
In a letter, the trust said this could have resulted in treatment being arranged sooner, but they said the outcome for the twins would still have been "uncertain".
A spokesman said: "We would like to offer our condolences to Ms Jaffray and Mr Bielicki at this difficult time.
"We have investigated their concerns and reported back our findings to them. We would urge them to contact us again if they have any further questions or concerns they would like us to address."