If there's a possibility of miscarriage how long will a pregnancy test show positive?

4-6 wks: Depending on when the miscarriage occurs, you pregnancy test can stay positive for up to 30-45 days, .

Several weeks: A pregnancy test will be positive as long as there is tissue in the uterus releasing hcg, or "pregnancy hormone". A growing pregnancy will always make hcg. A miscarrying pregnancy will still have a positive urine test, but may have a decreasing trend on a quantitative (numeric) blood test for hcg. Hcg will remain present for several weeks after a complete miscarriage.