You can test for pregnancy at home using an over-the-counter urine test or at a doctor’s office with a blood draw. Both methods detect hCG, a hormone your body starts producing after a fertilized egg implants in the uterus. Home urine tests are the fastest and most accessible option, while blood tests offer greater sensitivity and can measure your exact hCG level.
Home Urine Tests
Home pregnancy tests work by detecting hCG in your urine. You either hold the test stick in your urine stream for a few seconds or dip it into a cup of collected urine, then wait a few minutes for the result to appear. Most tests display two lines for a positive result and one line (the control) for a negative.
Not all home tests are equally sensitive. The most sensitive widely available test, First Response Early Result, detects hCG at concentrations as low as 6.3 mIU/mL, which is enough to catch over 95% of pregnancies by the day of a missed period. Other brands require significantly higher hormone levels to register a positive. Some need concentrations of 100 mIU/mL or more, which means they detect 16% or fewer pregnancies on that same day. If you’re testing early, the brand you choose genuinely matters.
When to Take the Test
Timing is the single biggest factor in getting an accurate result. After implantation, hCG levels start very low and roughly double every two to three days. At four weeks of pregnancy (which is around the time of your expected period), blood levels of hCG range from 0 to 750 µ/L. By five weeks, they climb to 200 to 7,000 µ/L, and by weeks eight through twelve they can reach 32,000 to 210,000 µ/L.
Because hCG rises so steeply, testing just a day or two later can make the difference between a negative and a clear positive. The most reliable time to take a home test is on or after the first day of your missed period. If you test earlier than that, a negative result doesn’t necessarily mean you’re not pregnant. It may just mean hCG hasn’t built up enough to be detected yet. If you get a negative but your period still doesn’t arrive, retest in two to three days.
How to Get the Most Accurate Result
Use your first morning urine whenever possible. Overnight, your urine becomes more concentrated, so hCG levels are at their highest. Drinking large amounts of water before testing dilutes the hormone and can turn what should be a positive into a false negative.
Follow the test’s instructions for how long to wait before reading the result. Most tests have a reaction window of about three to five minutes. Reading the test too early may show nothing; reading it too late (past about ten minutes) can produce a faint, colorless streak called an evaporation line as the urine dries on the strip. This streak is not a positive result.
Faint Lines vs. Evaporation Lines
A faint line that has color, even if it’s lighter than the control line, is typically a true positive. It usually means hCG is present but at a low concentration, which is common in very early pregnancy. A true positive line will be the same color as the control line (usually pink or blue, depending on the brand) and will run the full width and height of the test window.
An evaporation line, by contrast, is colorless. It looks gray, white, or shadowy and may be thinner than the control line or not extend fully across the window. If you see a questionable mark after the recommended reading window has passed, don’t trust it. Take a fresh test the next morning and read it within the time limit.
Blood Tests at a Doctor’s Office
There are two types of blood pregnancy tests. A qualitative blood test simply tells you whether hCG is present, giving you a yes or no answer similar to a home test but with higher sensitivity. A quantitative blood test measures the exact amount of hCG in your blood, reported in mIU/mL. In non-pregnant women, hCG levels are below 5 mIU/mL.
Quantitative testing is useful in specific situations. Doctors use it to estimate how far along a pregnancy is, monitor whether hCG is rising normally in early pregnancy, or help diagnose complications like ectopic pregnancies (where the embryo implants outside the uterus) or molar pregnancies (abnormal tissue growth). If your doctor suspects a problem, they may order two blood draws a couple of days apart to see whether hCG is doubling at the expected rate. For most people who simply want to know if they’re pregnant, a home urine test is sufficient, and a blood test isn’t necessary unless there’s a clinical reason.
What Can Cause a False Positive
False positives on home tests are uncommon but not impossible. The most straightforward cause is fertility medications that contain hCG itself. These injectable drugs are used to trigger ovulation during fertility treatments, and because they introduce the exact hormone the test detects, they can produce a positive result even without a pregnancy. If you’ve had an hCG injection, your fertility clinic will tell you how many days to wait before testing.
Certain other medications can also interfere with results. These include some antipsychotic medications, certain anti-seizure drugs, specific anti-nausea medications, and progestin-only birth control pills. A recent miscarriage or abortion can also cause a positive test, since hCG can take several weeks to fully leave your body.
What Can Cause a False Negative
False negatives are far more common than false positives, and the usual reason is simple: testing too early. If you test before your body has produced enough hCG to reach the test’s detection threshold, the result will be negative even though you’re pregnant. Drinking a lot of fluids before testing compounds this problem by diluting your urine.
In rare cases involving very high hCG levels, such as with molar pregnancies, something called the “hook effect” can actually cause a false negative. The hormone concentration is so extreme that it overwhelms the test’s antibodies, and the test fails to register a result. This is unusual and typically only occurs in abnormal pregnancies, but it’s worth knowing if a test comes back negative despite strong pregnancy symptoms and a significantly missed period.
What to Do After a Positive Result
A positive home test is highly reliable. Once you get a clear positive, the next step is scheduling a visit with a healthcare provider. They’ll typically confirm the pregnancy and estimate how far along you are, usually with an ultrasound rather than repeating a urine test. If you’re on any medications, that first appointment is the time to discuss whether they’re safe to continue. If you get a positive followed by a negative a few days later, or if you experience bleeding, contact your provider, as this can sometimes indicate a very early pregnancy loss.