Pregnancy tests work by detecting levels of human chorionic gonadotropin (hCG), a markers of pregnancy in a person’s urine or blood. Home tests can usually detect pregnancy 12–15 days after ovulation.

A person can take a test at home or a doctor’s office. Knowing which type of test is most suitable, and how it works, can help ensure that the results are accurate.

In this article, we describe the types of pregnancy test, how to use them, and what the results mean.

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There are two main types: urine and blood tests. Home pregnancy tests are urine tests.

Urine tests

Whether a person has one in a clinic or at home, these tests check levels of the pregnancy hormone called human chorionic gonadotropin (hCG).

This hormone starts circulating once a fertilized egg has attached to the wall of the uterus wall, which usually happens 6 days after fertilization.

Levels of hCG change throughout pregnancy. A urine test can typically detect hCG 12–15 days after ovulation.

Home pregnancy test

Home pregnancy tests are available over the counter, and they are typically inexpensive. If a person uses them correctly, they give accurate results.

These tests usually give results within 5 minutes, though the timing of different tests may vary.

A standard home pregnancy test has a strip that changes color or displays a symbol, such as a plus or minus sign, to indicate the result. Digital tests have a screen that displays “pregnant” or “not pregnant” or a symbol. Some can even indicate how far along the pregnancy is.

Clinical urine test

This involves going to a doctor’s office to give a urine sample. A person may opt for this to avoid some of the handling errors that can happen with home tests. Otherwise, the level of accuracy is the same as with home testing.

Like home tests, clinical tests look for the presence of the hormone hCG in the person’s urine.

Waiting times for clinical results vary. Some facilities provide results immediately, while others may take up to a week.

Blood tests

These are less common than urine tests, but they can give results earlier in a pregnancy.

There are two types. A qualitative hCG blood test checks whether the hormone is present in a blood sample. A quantitative hCG blood test measures the total amount of the hormone present in the person’s system and can detect even very small amounts of the hormone.

Anyone who can become pregnant and suspects that they are should take a test. This might be an especially good idea for people who have recently had sex without a barrier method of protection, such as a condom.

Some signs of early pregnancy include:

Learn more about the early signs of pregnancy here.

A person might have a pregnancy test in a clinic or doctor’s office. Depending on the test, this involves giving either a urine or blood sample. Healthcare professionals may test this immediately or send it to a laboratory for testing. The lab usually takes a day or two to return the results.

Home pregnancy tests are simple to use, but it is crucial to follow the instructions carefully. In general, they involve:

  • urinating directly onto the testing stick
  • urinating into a clean cup, then dipping the testing stick into this for a specified amount of time
  • urinating into a clean cup, then using a dropper to apply urine to an area of the testing stick

A person’s hCG levels change rapidly throughout pregnancy. It is often best to take a pregnancy test 1–2 weeks after the first missed period. A person may want to wait a bit and test again if they suspect pregnancy but receive a negative result at first.

Many home pregnancy tests claim to be accurate up to 99% of the time. A positive result is typically correct. A negative result is more likely to be incorrect.

However, these accuracy claims assume that the person has used the test correctly.

Most tests can produce accurate results on the first day after a missed period, but to ensure accuracy, it is advisable to start testing 1 week after a missed period.

For around 10–20% of pregnant people, a home pregnancy test does not accurately detect the pregnancy on the first day of their missed period. This might result from a person having irregular periods or miscalculating when their period was due.

But various other factors can influence the accuracy of pregnancy tests, including:

  • when the person tests, as hCG levels easier to detect first thing in the morning
  • the time since conception
  • the time since ovulation
  • how quickly the fertilized egg implants
  • how well the person has followed the testing instructions
  • how sensitive the test is

A positive result typically indicates pregnancy, while a negative result tends to mean that the person is not pregnant. It is more likely for a negative result to be incorrect.

It is important for anyone using a home test to follow the instructions carefully and understand what each color change or symbol indicates.

If a person takes a clinical test, a healthcare professional explains the results.

Positive result

A positive result indicates pregnancy. This is true even if the color change, word, or symbol on a home test is faint.

Anyone who gets a positive result should contact a healthcare professional right away.

Very rarely, a false-positive result occurs. This means that the person taking the test is not pregnant, but the test says that they are. False positives can occur due to:

  • the test kit having expired
  • certain medications
  • early pregnancy loss
  • ovarian tumors
  • liver disease
  • kidney failure

Negative result

A negative result means that pregnancy is unlikely. However, false-negative results are common.

A person who gets a negative result may be pregnant, and the test may not be detecting it. This can occur for a number of reasons, including:

  • taking the test incorrectly
  • testing too soon
  • testing with urine that is too diluted
  • using an expired or faulty test

Taking another test within 1 week is a good idea, whether the first result was negative or positive. However, it is especially important if the first result was negative, if there are any signs of pregnancy, or both.

When to see a doctor

Anyone with questions about pregnancy or their test results should contact a healthcare professional.

If a home pregnancy test result is positive, a doctor can confirm this with a clinical test. Next, it is important to make a prenatal care plan with the doctor, and this should include checkups throughout the pregnancy.

If a home pregnancy test result is negative, but periods do not resume, contact a healthcare professional to identify the cause of the missed periods.

Pregnancy tests measure levels of a hormone called hCG in a person’s blood or urine.

A person can buy home pregnancy tests over the counter or have a test that involves giving a blood or urine sample in a clinical setting.

Both home and clinical tests are reliable. Some manufacturers claim that their tests are up to 99% accurate. It is crucial to follow the instructions carefully, and it is a good idea to take a follow-up test within 1 week.