Born at just 23 weeks and four days, Annabelle and Imogen Weir were so tiny they could each fit in only one of their parents' hands.
The infants, thought to be the youngest twins ever recorded in Britain, were whisked away to intensive care after their premature births.
With their survival hanging in the balance, they had to spend their first four months in hospital as doctors battled to keep them alive.
Forced to undergo multiple blood transfusions and emergency surgery, they couldn't even wear clothes for fear their delicate skin might tear.
But now, nine months on from their births last April, the sisters are finally at home with their parents, Claire and James, in Renfrewshire, Scotland.
A laughing and smiling pair, they are still amazing medics with their progress.
The Twins and Multiple Births Association - who have supported the family - said today the identical twins are "truly incredible" and "a miracle".
Annabelle and Imogen, who live in Paisley, were born three days under the 24-week legal limit for abortion in the early hours of April 3, 2016.
Annabelle weighed just under a pound, while her twin was just over.
Their mum, Claire, 31, said: "They are the youngest and smallest surviving twins to be born in Scotland. I'd never heard of twins so small surviving.
"It didn’t seem possible for one, let alone two.
"The consultant told us that if the girls had been born just two years ago they wouldn’t have survived - that’s how fast medical technology is advancing.
"They have surprised everyone. They will always be our little miracles."
Claire and husband James, also 31, met at university in Dundee nine years ago.
They tied the knot in 2013 and were delighted when they found out they were expecting a baby in late 2015.
However, they hadn’t even considered the possibility they were having twins.
After some bleeding at seven weeks, Claire was given an early scan and the couple were told that there were two strong heartbeats.
James, a town planner, said: "We don’t have a history of twins as a family, so it was a shock. We were over the moon and pretty overwhelmed.
"Claire had to go back for regular scans because she had some other bleeds but each time we were told the babies were OK."
Claire’s 20-week scan showed that the twins were growing well.
But just a fortnight later, at only 22-and-a-half weeks, her waters broke.
Doctors at The Royal Alexandria Hospital in Paisley warned the couple that they would not able to provide resuscitation for the infants if they were born under 28 weeks, so Claire was transferred to Glasgow's Princess Royal Maternity Hospital.
While other mums on the maternity ward were eager for their babies to arrive, Claire was desperate to prolong her pregnancy.
The mother said: "I was just trying to keep the babies inside me for as long as possible. It was a really horrible time, filled with worry.
"I just tried not to move too much - I was even worried to go to the toilet.
"After 23 weeks, they would at least have a chance of resuscitation so I hoped they would stick in there. Each day brought more hope.
"I got to more than 23 weeks but then I got very ill with a sepsis infection and they had to induce me.
"The fact that they were twins, that I had an infection and they were so premature all lowered their chance of survival.
"I didn’t have a lot of hope."
In the early hours of the morning, Annabelle was born, weighing only 15.5oz.
Ten minutes later, Imogen arrived, weighing 1lb and half an ounce.
Claire, who had to undergo an operation because she had a retained placenta and was ill with sepsis, said: "They were whisked away to intensive care.
"I didn’t even get to see them.
"I got to hold Imogen after about six days but Annabelle was smaller and more vulnerable, so I didn’t get to hold her for a few weeks.
"They were so tiny they fitted in one hand. Annabelle’s foot was about the size of James’s thumbnail. I was petrified when I first held them.
"They didn’t open their eyes or cry for a few weeks. They couldn’t wear clothes for 100 days, just a nappy and hat. Their skin was too delicate."
The babies spent six weeks in incubators linked to a hi-tech positive pressure ventilator, which delivers air in gentle "breaths".
They also received caffeine to stimulate their breathing.
Today, both of the twins still receive oxygen through a nasal tube.
However, doctors expect them to come off it soon.
Despite being nine months old, the adorable girls weigh only 11 and 12lb and have to wear 0-3 month baby clothes.
Claire, a child psychiatrist, said: "We got Imogen home first, a couple of weeks before Annabelle. I just watched her constantly to make sure she was breathing.
"When Annabelle came home, after 138 days in hospital, we were more prepared.
"It was a terrifying experience but wonderful to be at home as a family.
"Now we are experiencing all the normal struggles new parents have, but we have loved every minute. We know how lucky we are."
She added: "The first big milestone was getting the girls off the ventilator, to know they were both able to breathe with just a small bit of additional support.
"That was a huge step because we still didn't know whether they would survive or not, if they couldn't cope. There have been so many milestones since.
"When they both reached 500 grams (1.102 lb) that was another, as they both lost weight after they were born and Annabelle went down to 400 grams (0.88 lb).
"Getting them back up over 1lb was nice.
"The nurses reassured us 'don't worry, all babies lose weight', but looking back they must have been thinking 'oh my goodness, these babies can't afford to lose more weight'.
"Then their first smiles after they came home.
"We were pulling funny faces and doing all sorts to get them to do it again. Now you can't stop them smiling - they're so funny.
"They're very contented and very happy.
"They are starting to take notice of each other. For a long time they would lie and look past each other but now they interact and it is just so cute.
"They are smiling and laughing and giggling.
"They are rolling over and starting to eat food."
Claire said Imogen is a "bit more bossy", while Annabelle is "laid back".
"It's amazing really," she said.
"There is no question, if it hadn’t been for the amazing doctors and nurses at both hospitals, they would have died.
"We can't thank them enough.
The couple have received support from the Twins and Multiple Births Association (Tamba), who said the twins' story was "truly incredible".
Helen Peck, Tamba's Scottish co-ordinator, said: "We are delighted for Claire and James and the twins. Imogen and Annabelle's story is just remarkable.
"They are truly incredible - a pair of miracles.
"To see premature babies born this early and go on to do so well is incredibly rare.
"It is a testament to the wonderful medical staff that they are now growing well."
