What is a pregnancy test? A pregnancy test is an easy-to-use diagnostic tool used to detect whether a woman is pregnant. It determines pregnancy by detecting human chorionic gonadotropin (hCG) levels in urine. Pregnancy tests usually consist of a special strip of test paper and a reader that detects the dark and light streaks that appear on the paper. Generally speaking, if there are two lines on the pregnancy test stick, it means that the woman is pregnant; if there is only one line, it means that the woman is pregnant.