"Late pregnancy"

I have heard alot of storys of women not finding out they are pregnant until they are at the 2nd or 3rd trimester. On 2 newspaper websites (not a hoax or a fake website) there was 2 women who didnt know they were preggo until they actually gave birth. I know 2 girls who didnt find out until they were at the 2nd trimester... Has this happened to anyone or do you know anyone ?