When the cramps started to kick in, Klara Dollan just assumed a painful period was starting.
She hadn't menstruated for several months, but was on the contraceptive pill continuously so hadn't thought anything of it.
There was no morning sickness, no back pain, no bump.
But yet the 23-year-old from London was pregnant - and her baby was on its way.
Dollan was at her first day in a new job as a sales executive at a marketing firm when the pain began.
After a 40-minute commute to her office in Waterloo, she launched into a two-hour meeting - all while the cramps were increasing in intensity.
She had to leave work soon after, but when she arrived home she realised she'd locked herself out of the flat she shares with her mother.
"Every so often there'd be this pain so bad I had to grab hold of the bannister," she told the Daily Mail of her two-hour wait for a locksmith. "The pains then stopped, but I couldn't stand still - I had to keep walking around, going up and down the stairs of my building."
Once she was back in her flat, Dollan spent 90 minutes pacing before realising the only place she felt comfortable was on the toilet.
"The pain suddenly became so bad I said to myself: 'I don't care, I'm going to have to scream'," she said.
A neighbour soon knocked on the door, and a heavily bleeding Dollan answered.
"I asked her to call an ambulance. Then I had this extremely painful urge to push: that's when the head came out. My neighbour was in the corridor and I was screaming: 'It's a baby, oh my God! It's a baby'."
Dollan welcomed a healthy 3.17kg daughter in her bathroom, then wrapped her in a towel.
"I couldn't believe I had a baby in my hands. I was in complete and utter shock."
The young mum was taken to hospital by the ambulance, where doctors confirmed both she and her baby were perfectly safe.
"Denied" or "cryptic" pregnancies occur more often that you may think, so much that they spawned their own television series (TLC's I Didn't Know I Was Pregnant).
A German study of births at all Berlin metropolitan area hospitals back in 1995 and 1996 showed that one in 475 women didn't know she was pregnant at 20 weeks, and one in 2455 gave birth to a viable foetus without realising she was pregnant until she went into labour.
The overall numbers are quite small - 62 for first group, and just 12 for the second - but they are enough to lead the authors to conclude that "the common view that denied pregnancies are exotic and rare events is not valid. Deliveries in which the woman has not been aware of her pregnancy until going into labour occur about three times more often than triplets".
A couple of other studies came up with similar numbers for 20 weeks' gestation.
Six-foot-tall Dollan gained 12.7kg during her pregnancy, going up just one dress size. She put the extra weight down to comfort eating following a break-up with her boyfriend of two years, Kris. Dollan believe she fell pregnant after vomiting up her pill one day while on holiday.
"I'd put on a bit of weight in most places, but I have a photo of myself in a bodycon dress at seven months pregnant and you wouldn't know it," she said. "The only thing I would say is I noticed the top half of my stomach was very hard when I touched it, about a month before the birth.
"I asked the midwife how it was possible - she said it had happened to plenty of women before, but mainly those who are overweight. My GP said I was not the first pregnancy like this he had dealt with."
Dollan is now adjusting to life with two-month-old Amelia, with support from Kris and her family.