Up to one in every 600 mothers-to-be remain unaware they are pregnant until they give birth.
Writing in the British Medical Journal, the researchers of a study said: "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."
Many mums find it hard to believe that a woman could go the whole nine months without even an inkling that she is pregnant. Most of us will experience some difficult to ignore pregnancy 'symptoms' like weight gain, backache, swollen ankles, morning sickness and difficulty finding a comfortable sleeping position.
But the mums in the gallery below thought they were having periods, had no visible bump and didn't notice a single kick!
On the one hand they were lucky - they avoided months of nausea, worry and backache. But on the other hand, they missed out on vital preparation time.
Pregnancy lasts nine months for a reason - to give you plenty of time to draw up a shortlist of baby names, to stock up on essential items and most importantly to give you time to get your head around the fact that you will soon be responsible for another human being.
Can you imagine what it must feel like... one minute you're happily going about your daily business and the next you have a fully formed little baby to look after, without so much as a missed period or a craving for pickles to serve as a warning!