The abbreviation stands for "human chorionic gonadotropin," a hormone associated with pregnancy. After conception, the placenta produces hCG, which in turn prompts the release of estrogen and progesterone, more hormones needed to sustain pregnancy. hCG is excreted in urine, so pee-on-a-stick tests are designed to detect its presence. If any is sensed, you'll get a positive result. hCG levels start out at zero and increase as the embryo grows. So if you test very soon after you conceive, you may get a negative test result or a very faint positive one. After a few days, if the pregnancy is viable, the results will be more definitive. A blood test can reveal the exact level of hCG in your system as early as 6 to 8 days after ovulation.