Most women can remember the exact moment they saw that plus sign on their home pregnancy test (HPT), flooding them with intense emotions. Whether you're planning a pregnancy, or it's a surprise, a home pregnancy test will probably be the first bearer of the news. According to home pregnancy test manufacturers, these tests - which detect the presence of the Human Chorionic Gonadotropin (hCG) hormone in the urine - are correct 99% of the time.

Pregnancy tests can register a positive as early as two days before a missed period, depending on the type you purchase. However, because different pregnancy tests are more sensitive than others, your best chance of getting an accurate reading is the week after your missed period. Reportedly, home pregnancy tests can miss approximately 85% of pregnancies when the test is conducted on the first day of a missed period.

HCG levels start climbing upwards from the moment of conception - but aren't detectable by home pregnancy tests for approximately 12 to 14 days after conception, which typically occurs somewhere around day 10 to 14 of your menstrual cycle. Some women turn to blood tests to detect pregnancy earlier - a blood test can detect hCG as early as six to eight days after conception. A Qualitative blood test will simply detect the presence of the hormone, while a Quantitative test will measure how much hCG is in the blood. This helps to determine if hCG levels are rising, or falling, as is the case with miscarriage.

A home pregnancy test is simple to use - be sure to follow the directions of the particular type you are using. A good rule of thumb is to use the test with your morning urine, which will have a higher concentration of the hormone in it, and will be less diluted. If you take it during the day, try to hold your urine for four hours and avoid drinking a lot of fluid to avoid dilution. After you've either held the stick in your urine stream, or dipped it in a cup of urine, the results will show in the result window, which is typically next to the control window. The control window shows a line to indicate that it is working properly. Some home pregnancy tests show a positive display with a plus, a line or a happy face, while others show nothing, or a negative sign. Newer home pregnancy tests use a digital display to take the guesswork out of trying to read a faint or partial line.

False negatives can be quite common on pregnancy tests, especially if you're taking the test too early for it to detect the hCG in your urine. False positives, however, happen less frequently. These can happen if you're using hCG as a fertility treatment, or if you're having a miscarriage, and didn't know you were pregnant. Certain tumors cause a release of hCG, and may trigger a false positive on a home pregnancy test.

If you think you may be pregnant, or are actively trying to get pregnant, have a few home pregnancy tests on hand. Buy several different brands, and do two tests. If you get a negative test, and it is around your missed period, then wait a week and try again.