The half life of marijuana in the body to show up on a test averages 45 days but can be longer. If you tested positive you are definitely inhaling enough to register a level in your blood. Only time and not smoking, or staying very far away away from secondhand smoke, will eventually make your test negative. Certain states have reporting rules if a baby tests positive on a blood test for any kind of drugs, so you may need to document a negative test before the birth in order to avoid problems.