Oh my god, I remember seeing a movie once where this happened and I thought it was fiction. I am astounded to read the advancement of medicine which can even make a person size increase as if they were pregnant. I have heard of "person with pseudocyesis" who may feel pregnant and have signs of pregnancy, but a pregnancy test, blood test or ultrasound will show they aren’t pregnant. https://my.clevelandclinic.org/health/diseases/24255-pseudocyesis
But then tricking a person for a whole 9 months is unbelievable.