Hours after finishing work at Croydon University Hospital in London, Claire Clarke-Wood, 28, from Hawkhurst, Kent, delivered baby Esmay in her bathroom.
Her contractions came so quickly there was no time for her to make it to hospital.
Baby Esmay was born before paramedics arrived, just after 07:30 GMT on 11 December, weighing 6lb 12oz (3.06kg).
“Me and my colleagues had joked: ‘Wouldn’t it be funny if I ended up delivering my own baby?'” Mrs Clarke-Wood said.
“But never in a million years would I have thought it would actually happen.”
The first-time mother said she had just finished a 13-hour shift at the south London hospital.
“It was very busy and we had quite a few deliveries that day,” she said.
“I went to bed as normal and at around three o’clock, I had a bit of backache and thought it might just have been from work because you bend over a lot.”
She said she had woken up her husband Tim at about 05:00 GMT when regular contractions began.
“I went to have a bath to see if that would settle things but things carried on very quickly,” she said.
“I got to the point where contractions were very close together and thought I’d check to see what stage I was at, and lo and behold the baby was coming.
“I never thought I’d be that far gone. It was very quick and unexpected, particularly for someone who’s quite petite.”
Mrs Clarke-Wood crouched in her bathroom using her mother’s make-up mirror to deliver the baby.
She said she “went into autopilot”.
“My husband came to find me and I was clearing up towels and making cups of tea.”
She said Esmay, who was born “a bit over three weeks early”, was “doing really well”.