How does ic/pbs affect pregnant women?

Doesn't . No direct effect on pregnancy, a few cases have reported temporary improvement during pregnancy. Elmiron (pentosan) is category b, considered safe. All medications would need discussion with your doctor.
Not much. The real question is how does pregnancy affect ic/pbs. For that answer, there is not a lot of great research. Traditionally, 1/3 improve, 1/3 worsen, and 1/3 notice no difference. I'm not aware of any data showing ic/pbs affects pregnancy other than reluctance for intercourse to achieve the pregnancy.