How reliable is the prometheus test for diganosing ibd? doctor can't do colonoscopy bc of pregnancy, but test came back positive.

Somewhat reliable: You are right when you say that colonoscopy with biopsy is the gold standard & would be preferable. Prometheus testing in the lab takes a combination of "markers" (blood reactants to inflammation in the bowel & genetic markers) & comes up with a probability estimate of inflammatory bowel disease: Crohn's or ulcerative colitis. It isn't 100%; your doc will have to interpret.