Little did she know that she was going to give birth to a little giant.
When Jack arrived at 37 weeks he weighed an astonishing 14lb 8oz.
Health problems kept him in the hospital for 4 months after his birth.
Tests showed that Jack had grown so big because of a condition called hyperinsulism which causes the body to produce too much insulin, leading to weight gain.
His heart muscle had thickened since it had to work extra hard because of his size.
At the age of 14 weeks he had 95 per cent of his pancreas removed to treat his condition. The operation was a success and doctors allowed him to go home with medication.
Today, Jack weighs nearly 22lb, compared with the average weight at six months of 16lb, and wears clothes for a child aged 12 to 18 months.
Sara describes him as “such a happy baby, always laughing and giggling. People can’t believe that he’s only six months old when I take him out in his pram.”