How do I know if my mare is pregnant without a vet?

I have a ten year old paint and I think she might be pregnant but I want to be more then 50% sure before I take her to a vet. She's a rescue horse and I'm concerned that because she was malnourished severely the foal may be dead. And i'm measuring her belly and I've noticed that her belly protrudes more on her right side then the left. help