At birth little Janey Blake weighed just 1lb 2oz and was given a one percent chance of survival by her doctors.
But now the bubbly three-year-old from Garston is getting ready to start her first day of school.
Proud parents Stephen and Kim said Janey, who celebrates her fourth birthday tomorrow, has shocked everyone by beating the odds.
Kim, 36, said: "It’s a miracle she pulled through. The chances she was given were near enough non existent.
"And now she’s absolutely fine, she has really shocked everybody."
Janey stopped growing 20 weeks into the pregnancy because of a condition called intrauterine growth restriction (IUGR), which left her umbilical cord like cotton wool.
Kim was admitted to specialist neonatal hospital Addenbrooke’s in Cambridge.
Four times doctors prepared her for theatre, but changed their mind at the last minute to allow the pregnancy to go on as long as possible.
The heavier Janey was, the better her chances.
At 30 weeks - after Kim had been in the hospital ten days - doctors had to deliver. Janey’s birth weight was a dangerous 1lb 7oz, which dropped to 1lb 2oz.
Mum-of-three Kim said: "The doctors said we would only have an hour or two together after she was delivered.
"They gave her a one percent chance of surviving the day."
But the little fighter surprised everyone and pulled through, even battling off a life threatening infection at just a week old.
Kim, who is also mum to eleven-year-old Jason and ten-year-old Jodie, continued: "She was very, very small. She couldn’t have milk for five days, and then only half a millilitre - I think it was two drops.
"We very nearly lost her when she had the infection. When I came in that morning I knew instinctively she was seriously ill. She needed a blood transfusion, but she fought it off."
When she was two kilograms, Janey was transferred to Watford General.
After three months in hospital, she was allowed to go home - just in time for older brother Jason’s birthday.
Now Janey is excited to start at Alban Wood Primary School full time in September, already proudly stomping around in her uniform.
Kim said: "She’s a little small, but it is nowhere near as noticeable as maybe a year ago. Sometimes people do a double take when they find out her age, but she’s happy and healthy.
"Everything they told us about the various problems she would face because she was born so small was all wrong.
"She’s come through everything, it’s amazing."