Is there a way to find out if someone has ever been pregnant?

Yes, sort of. Is this about someone you know?

Define pregnant? Carried a child to term? Had a fertilized egg implant? Does this include abortions or miscarries?

I think the question for me is why you want to know? And why is asking the person NOT an option?

No, there is not a medical test that will determine if someone was ever pregnant.