Many women who think they might be pregnant, or have been trying to get pregnant, want to know for sure as soon as possible. Home pregnancy tests that detect the presence of hCG, often called the pregnancy hormone, in urine can offer a convenient way to find out. In order to get results that are as accurate as possible, people need to understand how soon they can use the tests and carefully follow the manufacturer’s directions.
Although doctor's offices can also perform urine pregnancy tests, many women prefer to use a home test first, then call their doctor to confirm a positive or unclear result. Not all brands of home pregnancy tests are equally sensitive. Some early-result urine tests can confirm pregnancy up to five days before a woman misses her period by detecting variants of the pregnancy hormone. While these tests can give early results for some women, they may not work that soon for everyone.
Most home pregnancy tests can give accurate positive results within a few days after a women misses her period. Early-result tests that claim to work up to five days before a missed period may give reliable positive results, but not reliable negative results, during this time. For example, one popular brand of early-result test states that while it’s 99 percent accurate at detecting pregnancy by the day of a women’s expected period, only 58 percent of women who turned out to be pregnant got a positive result four days before their expected period. Three days before, 80 percent got a positive result, and by two days before, 90 percent did. By one day before their expected period, 94 percent of women got a positive result.
Urine pregnancy tests work by detecting a hormone known as hCG, or human chorionic gonadotropin, that the body starts producing once the developing embryo implants itself in the uterus. This happens about one week after fertilization takes place. Early result tests may also detect a variant of this hormone, hCG-H or hyperglycosylated hCG, that occurs slightly earlier. Since the level of hCG rises significantly during early pregnancy, and may double every few days, urine pregnancy tests generally become more accurate later after fertilization than they are early on.
Women who have already missed their period can choose just about any brand of home urine test for pregnancy. Women who have not yet missed their period may want to try an early-result test up to four days before their expected period, with the understanding that they may need to test again later if the results are negative. The cost of pregnancy tests can vary widely between brands and stores, and some brands of pregnancy tests are less expensive in multipacks. Women who use early-result tests may benefit from buying a multipack, since they may need to test several times before getting a final positive or negative result.
Women who receive a negative result on a urine test for pregnancy may want to wait several days to a week, then test again. While false positive tests are rare, many women who get an early negative result may get a positive result later. Some situations, such as ectopic and chemical pregnancies, can cause false positive or unclear test results. Women who have unclear test results, or still have not had a period a week after the expected date, should contact their doctors, who can check for pregnancy or problems that might cause the missed period.