Are house accidents common if a dog is going into heat?

I have never heard of urination accidents if a dog is going into heat. she may have a urinary tract infection and is trying to tell you by showing you something isn't right. she can still get fixed if she is already in heat. some vets don't like to do it though because her female parts are swollen so the vet has to look a little harder to find what needs to be tied off. And I don't want sound like a meany, but she can also be fixed if she is pregnant. I work at an animal shelter and the less we bring accidental and unwanted pups into the world the better off they will be.