Zoe, now four months old, defied expert opinion when she was born at Simpson's Memorial Maternity Hospital in Edinburgh.
Her mother, Joanne McAleese, 26, was taken to hospital on 27 July with high blood pressure but four days later doctors told her that they would have to risk delivering Zoe by Caesarean section.
She was so small her mother was not allowed to hold her because she was too weak and the only parental contact was through gentle stroking while Zoe clung to life in the incubator. But Zoe, who weighs 2.77kg, has been declared well enough to go with her mother and father, Colin, 28, to their home at Addiewell, West Lothian. Yesterday Ms McAleese said: "I could see from the doctors' faces they were concerned but I didn't realise both me and my baby's life were in danger.
"When they lifted her out I could see a tiny glimpse of her and she was wriggling about, so I knew she was alive. Then, as they rushed her away, I heard her cry, which I knew was another good sign. But I was so ill I didn't see her until the following day and when I did my heart just melted. She was so much smaller than even the other premature babies I had been shown. She was so tiny I could have held her in my hand. At eight weeks I was allowed to hold her for the first time and it was the happiest moment of my life. The nurses placed her on a cushion on my knee."
A consultant, Ben Stenson, said: "She was the smallest baby we had ever looked after. We are absolutely thrilled that Zoe is doing so well.
A baby as small as she is has to overcome an awful lot and has to have a great deal of strength and courage, as do the parents."
Britain's smallest surviving baby was Marianne Taggart, who weighed 10oz when born in South Shields, Tyne and Wear, in 1938.
The smallest baby to have survived weighed 9.9oz and was born in the US in 1989, according to The Guinness Book of World Records. A baby has to live for a minimum of 29 weeks to qualify for the title.