Premature twins Grace and Olivia Oman have defied the odds to start school
The little girls, who should have been triplets, were smaller than the palm of their mum's hand and weighed just 1lb 14oz when they were born three months early in July 2013.
Doctors told parents Vicki, 32, and Mark, 30, from Morpeth, Northumberland, there was very little chance the tiny tots would even live an hour.
The devastating news came as the parents were still grieving the loss of a third baby who had died when Vicki was 14 weeks pregnant.
But battling Grace and Olivia proved doctors wrong and now four years on they are due to start school on Tuesday.
Proud mum Vicki describes the plucky siblings as her "determined little miracles".
She said: "We can't quite believe we have got to this point, it is quite surreal. We are so lucky to have them here.
"The doctors didn't know if they would survive an hour, never mind four years and having them start at school. They have come on so far.
"They came into the world fighting, they are very determined little girls and don't give up easily. They take everything that's been thrown at them on the chin."
Vicki and Mark, who also have six-year-old son, Jake, were originally due to have triplets but sadly the third baby, who the couple named Eleanor, died when she was 14 weeks' pregnant.
While still grieving for the loss, the waters around Grace then broke and it was feared the family would lose her too because her lungs wouldn't develop properly without the fluid.
But the waters built back up and everything seemed stable.
Then at 26 weeks, Vicki was rushed to Wansbeck General Hospital with contractions and in the early hours of July 26 she gave birth to the identical twin girls.
The twins were born just over an hour apart in July 2013 weighing just 1lb 14oz and the couple were warned it would be touch and go whether they would survive.
They were transferred to the neo-natal intensive care unit at Middlesbrough's James Cook Hospital, where they stayed for the next 14 weeks.
But, on November 6, 2013 the twins were split up when Olivia was discharged and Grace was moved to Newcastle's RVI as she still had problems breathing.
At the age of just eight weeks and weighing just 3lb, Grace was fitted with a tracheostomy - a surgically made hole that goes through the front of the neck into the trachea, or windpipe to help with breathing.
She was allowed home for the first time aged nine months and has since had the tracheostomy removed following reconstructive surgery of her airway using rib cartilage.
The brave youngster is beginning to live a normal life and her speech - hindered by her ordeal - is beginning to develop.
Vicki said they are now looking to the future as the girls have reached the milestone of starting school.
**WATCH: Actor Chris Pratt shares the story of his son's premature birth **
She said: "We still have some small hurdles to face, especially Grace, but we will continue to get through them like we have the last four and a half years.
"We don't take anything for granted and know how lucky we are to have them with us.
"They are looking forward to starting school; it is going to be an emotional day and there will be tears."
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