Sheila Beeson, 29, worked at the London home of James Longcroft, an accountant, and his wife, Anita, a lawyer, when the incident was alleged to have happened, the Old Bailey was told.
In the six weeks she had been employed as a nurse for their baby son, also called James, the relationship between her and the family deteriorated.
Ms Beeson, a qualified state- enrolled nurse, said she had been awake all night as James had cried constantly. The last straw was when Mrs Longcroft returned from the doctor with James and her two other children and told Ms Beeson it did not need her and another nanny to take off James's outdoor clothes.
Counsel for the prosecution has alleged that Ms Beeson swept past her employer and up the stairs, then she turned on the third or fourth step and threw James at his mother, saying 'you can keep your damned baby, I have had it'.
Ms Beeson denied throwing him.
She said she had always got on with previous employers. Several references were read describing her as 'a reliable, honest worker with a good personality'.
She had never before decided to walk out of a job. But substantial tension had built up and she disapproved strongly of some of the Longcrofts' instructions.
Ms Beeson, of Warburton Road, Thornhill, Southampton, denies child cruelty.
Linda Kelsey, the editor of She magazine, told the court Ms Beeson looked after her son Thomas for two years and she had never had cause to complain.
The trial resumes today.Reuse content