If anyone can believe it, and trust me when I say my family didn't, my cousin didn't know she was pregnant until she was in labour.
We have asked countless times how she didn't know and she does cop to a lot of denial, but also she was quitting smoking, working a lot trying to lose weight etc. Attributed the lack of regular periods to all that (she said she did have some periods). She is a curvy girl so she didn't notice movement she says, and I can say honestly no one in her family who saw her regularly knew. Wasn't until her mom took her to the ER cuz she couldn't drive due to stomach pain and saw her bare stomach it clicked. Her sons now 2.5 and totally healthy lol.
I guess it happens, congrats though!!
Similar happened to a friend of mine from uni, her dad was posting on FB that they were taking her to A&E because she had horrific stomach pains, then posted a pic of her with cannulars in, the next picture came a day later, surprise baby! She is curvy but didn't look like she'd put weight on, going by her FB pictures. She'd gotten a new, very physical job and taken up rock climbing so I guess she was losing weight whilst putting on baby weight, staying the same size! She was literally scaling a massive cliff the day before giving birth!