Sisters Charlotte and Emily Hinch were born two and a half years apart – but amazingly, they are non-identical twins.

Frozen in time, the "time warp twins" went on an extraordinary journey to come into this world.

When parents Lisa and Julian Hinch had IVF treatment in 2004, they had three embryos frozen to give them a chance of a second child.

Charlotte was implanted immediately, but Emily was one of the batch kept on ice – at minus 196 degrees in liquid nitrogen.

And because the eggs the embryos came from were released at the same time, Charlotte (2), and three-month-old Emily are non-identical twins.

There was a 35 per cent chance of the treatment working the first time and 10 per cent chance with the second treatment.

Mrs Hinch (36), of West Road, Tallington, near Stamford, said: "Charlotte has been a blessing. We can't imagine life without her and we couldn't rest knowing that there were three potential Charlottes sat in a freezer."

Her husband (42) said: "We didn't expect it to work the second time. It was a real rollercoaster ride."

Now they hope their experiences will inspire other couples to persevere with fertility treatment.

They went to see their doctor in 2001 after struggling to conceive naturally.

Lisa was diagnosed with polycystic ovary syndrome, which can cause fertility problems.

They were treated by the firm Care Fertility at the Fitzwilliam Hospital in Peterborough and in Nottingham.

After a nervous five-week wait, they saw Charlotte's heartbeat during a five-week scan.

Lisa said: "They say watching the cells multiply before planting is emotional, but the most emotional part was seeing the heartbeat."

Charlotte was born on August 2, 2005 by Caesarean section weighing 6lb 7oz and Emily arrived on February 17 this year weighing 7lb 14 oz.

Lisa said: "We adore them. There's not a day we don't tell them we love them."

The girls are the third generation of twins in the Hinch family.

Julian has an identical twin and his mother was also a twin.

The treatment cost £7,000 which they funded by remortgaging their home.

Lisa, who hopes to become an egg donor, said the support of the staff at Care Fertility was invaluable. She said: "We want people to know that it can really work and it really is worth trying."

Dr Simon Fishel, who is managing director of Care Fertility, who has treated a woman who had twins 25 years apart, and was part of the pioneering team that helped create the first test-tube baby Louise Brown. He said: "It's great for them."