Susan Tollefsen, from Romford, east London, was sent to hospital for emergency tests on her swelling belly eight weeks ago, but was instead congratulated by the sonographer who told her she was almost 30 weeks pregnant.

She will become one of Britain's oldest mothers when she gives birth to a baby girl, who she has already named Freya, by caesarean section next week.

She said: "We're very excited about it. It's our miracle baby."

The pregnancy follows several years of attempts by Ms Tollefsen, a special needs teacher, and her partner, Nick Mayer, 46, a warehouse manager, to have a baby by IVF treatment in foreign clinics, they told the Daily Mail.

Ms Tollefsen said she was referred to hospital after an examination by a private GP revealed a "hard abdominal mass".

She had just undergone an examination at the private Nuffield Hospital in Brentwood, Essex, when the sonographer turned to her and said 'congratulations', she said.

The couple thought their hopes of having a baby through IVF were over when Ms Tollefsen suffered an apparent miscarriage within four weeks of two fertilised embryos being implanted at a Russian fertility clinic.

She said her GP told her she had miscarried and a blood test and home pregnancy test appeared to confirm this by showing negative. She now believes she miscarried one of the twins and the other survived.

All the scans had shown the baby was developing normally, Ms Tollefsen said.