1. The basic principle of how long it takes to detect pregnancy using test strips. How long does it take to detect pregnancy using test strips? Generally speaking, women can detect pregnancy through hCG (human chorionic villus) in urine about 10-14 days after conception. hCG is a hormone produced by the embryo and placenta. It begins to be secreted after the fertilized egg implants, and gradually increases as the pregnancy progresses. The principle of the test strip test is to determine whether you are pregnant by detecting hCG levels in urine. 2. What