How do I know if I have a bladder infection while pregnant?

Urine culture. You need to have a test called a urine culture. It takes a few days to get the results but it is very accurate.
Symptom-based. If you notice strong/foul odor; have burning w/urination; need to go repeatedly (but nothing there--not just from bladder compression w/pregnancy); fevers; low midline abdominal pain, etc., should get urine tested.