Sometimes, people who are pregnant don't know or believe that they are actually pregnant. They might not feel any different, or they might not want to be pregnant, so they pretend it's not happening. This is called the "denial of pregnancy".
You know how sometimes you might not want to do something, like take a bath or eat food you don't like? Well, some grown-ups might feel the same way about pregnancy. But pregnancy is not like taking a bath or eating food - it's something that grows inside a woman's belly, and it's really important to take care of it.
It's like having a secret that only you know, and sometimes it can be hard to tell other people about it. But it's important to talk to a grown-up, like a doctor or a teacher, so they can help take care of the baby and make sure the mom is healthy too. Even if it feels scary or difficult, it's always better to ask for help.