When Archie and Harley Garthwaite were born at 23 weeks with holes in their hearts, their parents were told to expect the worst.
The twins weighed just 1lb 4oz and 1lb 6oz each and doctors said it would be a miracle if even one of them survived unscathed.
As well as the holes in their hearts, the boys, who are not identical, had bowel problems and were unable to breathe for themselves.
At just two weeks old, Archie had to undergo gruelling open heart surgery, with his brother following a fortnight later.
Medics also operated on them both to correct bowel problems, performed laser treatment to stimulate their underdeveloped eyes, and put them on ventilators and oxygen to help them breathe.
And despite the odds being stacked against them, the twins have clung to life.
Their mother Hayley Kennedy, 20, said: ‘It was the scariest time of our lives.’
Miss Kennedy, who is engaged to the children’s father, Billy Garthwaite, had a smooth pregnancy until her waters to Archie’s sack broke at 21 weeks.
The couple, who live in Hartlepool, County Durham, spent the next two weeks at the University Hospital of North Tees in Stockton with doctors desperately trying to prevent Hayley going into labour, due to the risks of giving birth too prematurely.
But at 23 weeks, Miss Kennedy began suffering cramp-like pains and realised Archie’s arrival was imminent.
He was born 15 minutes later and placed straight into an incubator and onto a ventilator. Harley arrived two-and-a-half hours later.
It soon became clear that both boys had holes in their hearts. They underwent risky three-hour heart and bowel operations at the Royal Victoria Infirmary in Newcastle.
Miss Kennedy, who was originally given a due date of last week, said: ‘The doctors told us to be prepared to lose them because the chances of even one of them surviving the surgery was so small.
Archie, who now weighs 5lb, has been allowed home, but requires a round-the-clock supply of oxygen.
At 4lb 8oz, Harley is still in hospital but should be discharged over the next few weeks.
‘To get to this stage with one of them home and the other almost ready to come home is just mind-blowing,’ said Miss Kennedy. ‘We never thought we’d get to this stage.
‘I am the proudest mum in the world and they’re our little miracles.
‘We are so lucky to have them both with us and I wouldn’t wish what we have been through on anybody.
‘I cried every night because I couldn’t hold my babies, we weren’t allowed to touch them. I didn’t feel like a proper mum.
‘Now after everything they have been through, we just can’t believe they are still here.’
She added: ‘Archie is laid back and quiet like Billy, but Harley is bad-tempered and loud like me.’
Dr Chidambara Krishna Iyer Harikumar, a consultant neonatologist at the University Hospital of North Tees and the doctor who helped deliver the babies, said they are the only set of twins he has ever known to survive being born so prematurely in his 20-year career.
He described the miniature pair as ‘unique and a complete rarity’.
He said: ‘Only about one in 10 babies born at 23 weeks survives and of those who make it, one in two of them will be brain damaged.
‘Therefore we’re talking about just one out of 20 babies will come out of this without damage.
‘For both twins to make it and to make it without brain damage is very, very rare to say the least.
‘In fact, I am not aware of any 23-week twins surviving in this region and it is definitely a first in this hospital.
‘I was there when they were born and I did not think they would survive, they were very, very small, and had very thin skin.
‘They have had some complications and operations in the early days, but it is heartening to know that both of them have come out of this winners and virtually unscathed.It is just amazing.’