Is a cryptic pregnancy a real thing?

Hey everyone, I need your help proving a point to my boyfriend. I was telling him about cryptic pregnancies and he firmly believes that it's fake. I've shown him videos, googled information on it and he still doesn't believe me. It someone can prove him wrong and explain how a cryptic pregnancy works that would be amazing.

Edit: my boyfriend had asked that I specify my question, he wants to know if a woman of an average height and weight is able to have a cryptic pregnancy and if they would have any birth defects or complications.