Ok, so there are women who don’t know they’re pregnant until they give birth. This is called a cryptic pregnancy, and can be caused for several reasons including unconscious denial by the mother.
There are also women who believe they are pregnant, despite no evidence. Pregnancy tests and ultrasounds are negative. These women believe they can be pregnant for up to 5 years… with few symptoms and no positive tests. In my searching, there is no medical evidence for these cases, although there are several on the other type, where women don’t know they’re pregnant until a baby is born.
Humans are weird.
https://www.kidspot.com.au/parenting/real-life/reader-stories/meet-the-women-who-believe-theyve-pregnant-for-years/news-story/6fdacb4c57d2b8e342725d40ea59bf02