Liz and Jeff Barrett were devastated when they lost their daughter Mollie just two days after Liz went into premature labour at 23 weeks.
But they were thrilled and amazed when her smaller twin Freya-Grace refused to give up the battle for survival despite only weighing 13oz at birth.
Over eight months she had nine blood transfusions, a plasma transfusion, and a delicate heart valve operation.
Britain's smallest twin: Liz with newborn Freya-Grace, who weighed just 13oz at birth
The feisty youngster was allowed home from hospital today to Deri in South Wales with an oxygen supply to help strengthen her lungs.
Many hospitals leave babies born before 24 weeks to die because they only have a two per cent chance of survival and often have severe disabilities.
However, doctors are hopeful that Freya-Grace will go on to live a normal life.
Mrs Barrett said: 'We are so proud of her. It's just fantastic Freya-Grace is home and putting on weight every day.
'She already brings us so much joy and her fighting spirit has got her through.'
Liz and her self-employed builder husband Jeff, 33, kept a cotside vigil - taking it turns to be with their little girl.
When their daughter was born she fitted easily into Liz's hand and her skin was so transluscent some of her veins were visible.
Home at last: Freya-Grace, pictured with her mother Liz, has left hospital today weighing nine pounds - still less than some full-term babies
Customer service advisor Liz said: 'At first, we were shocked that Freya had survived - she was the smallest of the two girls.
'We thought the doctors had made a mistake - we thought Mollie was going to live.
'When I saw Freya, she reminded me of cooked chicken. She was so small. Her skin was shiny, you could almost see straight through her.
'She didn't look like a normal baby should. It was horrible to see her hooked up to all these wires. I wanted to hold her but she was too fragile to touch.'
But she said her brave little girl is living proof that babies are viable at 23 weeks.
She is furious after a leading consultant questioned whether babies should be resuscitated when born at 23 weeks.
Dr Daphne Austin, of the West Midlands Specialised Commissioning Team, told a BBC documentary that rescuscitating '23-weekers' was doing more harm than good.
Liz, who became pregnant through IVF treatment, said: 'I was infuriated by her comments.
'I would like to meet Mrs Austin, ask her to look into Freya-Grace's eyes then ask whether she thinks treating 23-week babies is a waste of money.'
Liz and Jeff say they will always be grateful to the doctors and staff at the specialist neo-natal unit at Singleton Hospital, in Swansea, where Freya-Grace spent her first eight months.
Freya-Grace weighs in at 9lbs now - still less than the birth weight of many babies.
Liz said: 'She's a determined little girl. She's already pulling herself up and arching her back. She's so strong.
'Every milestone that Freya reaches is that little bit happier, I'm just so grateful she's still here.'
The previous smallest surviving twin born in Britain was in July 2010 to Amanda Staplehurst in Portsmouth to a boy weighing 1lb 4oz. His sister, weighing 1lb 20z also survived.