Whether you're trying to get pregnant or not, a missed or late period can feel like reason enough to take a pregnancy test. It makes sense that you'd want an answer ASAP, but you might want to pause before you wee on a stick. If you take a test too early, there's a chance you could end up with a false negative.
So, when should you take a pregnancy test? Ideally, the best time to take a home pregnancy test would be the day after your missed period — in other words, a full week after your first missed day, according to the Mayo Clinic. Tricky to be patient, but worth waiting. Taking a test at this time ensures that your results will be the most accurate they can be, which is around 99%, according to a 2014 study (and pretty much every pregnancy test box).
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Here's why the timing matters: When a person becomes pregnant, a hormone called human chorionic gonadotropin (aka hCG) is released into their bloodstream, and then makes its way into their urine, according to Medline Plus. Home pregnancy tests are designed to pick up on the presence of hCG, while pregnancy tests that you have done in the doctor's office can determine the amount of hCG in your blood (which indicates how far along the pregnancy is). At first, the amount of hCG in a pregnant person's urine increases at a rapid rate of about 50% each day. So, if you take the urine test before your body has produced enough hCG for it to be detected in your pee, then you could end up with a false negative, according to the Mayo Clinic.
Most home pregnancy tests aren't sensitive enough to detect hCG before or on the first day of a missed period, according to the 2014 study. Although many tests claim to give an accurate reading early on in pregnancy, you may take that promise with a grain of salt once you understand how the tests actually work. If you've already taken a test which came out negative, definitely take another one if it's been a week and your period still hasn't shown up.
False-positives are possible, too, according to the Mayo Clinic. For example, if you're taking fertility drugs that contain hCG, that can mess with the test. Or, if you recently had an ectopic pregnancy or lost a pregnancy, the test can be inaccurate. A false positive is a very rare occurrence, while a false negative is as easy as taking your test a day too soon.
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If you simply can't wait, you could head to your doctor to get a blood test, which tends to be more sensitive. (Your doctor also should be well versed in your medical history, including your menstrual cycle, so they might have more insights into whether you could be pregnant.)
To make sure that you're getting the most accurate read from a pregnancy test, take it first thing in the morning, while your urine is extra-concentrated, the Mayo Clinic recommends. Be sure to follow the instructions that come with the test, and wait long enough before you look at the reading. While it might be stressful to have to wait that extra day or week, it could mean the difference between a false-negative and a totally accurate test — and that's worth it, right?