What Is a Blood Pregnancy Test and How Does It Work?

A Quantitative (hCG) or Blood Pregnancy Test Tells a Great Deal

A close-up of a pregnant woman's arm at a medical office
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In This Article

Most pregnant women find out they are pregnant by taking a urine-based home pregnancy test. Sometimes, doctors suggest that you also take a blood pregnancy test. In specific cases, there are multiple reasons why a blood test may be preferred, but usually, a urine test is all you need. Below, we explain exactly what a blood pregnancy test is and how it differs from a urine test.

Overview

A blood pregnancy test is usually a quantitative blood test that shows how much human chorionic gonadotropin (hCG) is in your blood. This is the type of blood pregnancy test that most people are referring to when they talk about blood tests for pregnancy. To test your blood for hCG, a simple blood sample is taken from one of your veins, usually in the arm, through a procedure called a venipuncture.

HCG is a hormone secreted in pregnancy and detectable beginning a week to two weeks (or more) after conception, depending on the test. Whether using a home pregnancy test that uses urine or a blood pregnancy test from your doctor, the results will be based on measurements of this hormone in your urine or blood. Both types of tests are very reliable, producing about 99% accuracy when used correctly.

What's the Difference?

A pregnancy blood test is more sensitive than a urine test and can offer more information. Most blood tests can detect slightly lower amounts of hCG, which means they can tell if you're pregnant a few days earlier. Urine tests tend to require slightly more hCG to read positive, making false-negative results a bit more likely with urine tests, although the rates are quite low overall.

Urine hCG Test
  • Needs slightly more hCG for a positive reading

  • Qualitative test

  • Tells you if you are pregnant or not, not how much hCG is in your blood

  • Accurate a few days to a week after a missed period

Blood hCG Test
  • Slightly more sensitive than urine tests

  • Can be qualitative or quantitative

  • Can track hCG levels over time

  • Can be accurate before a missed period

Qualitative Tests

Urine tests are qualitative, meaning they either detect hCG in your blood, giving a positive reading, or they don't, which is a negative reading. You may also have a qualitative blood hCG test to measure hCG in your blood. Again, the results are very clear: yes, you are pregnant because we found hCG in your blood or, no, you are not pregnant because we didn't find it.

Urine pregnancy tests can usually detect pregnancy by about 10 days after conception. Blood pregnancy tests can pick up hCG in the blood six to eight days past ovulation.

It's recommended to wait a week (or at least a few days) after a missed period before taking a urine pregnancy test for optimal efficacy.

Quantitative Tests

Another option is getting a quantitative hCG blood test (also called the beta hCG test). These tests can give your doctor or midwife more information than just whether or not you're pregnant. Quantitative hCG tests can pick up even tiny amounts of the hormone and measure exactly how much hCG is in your blood. This information can be compared over time.

In general, your hCG levels will nearly double about every two days in early pregnancy.

By having multiple blood tests about 48 hours apart, your doctor can track your hCG levels to get a better read on your pregnancy, if needed. These serial blood tests can help your provider monitor your pregnancy for miscarriage or ectopic pregnancy as well as the possibility that you’re carrying multiples.

Due to stress, expense, and other factors, these tests are not done routinely (or needed) for every pregnant woman. Talk to your doctor or midwife if you think that a blood test for pregnancy is right for you. If your specific circumstances don't warrant a blood test, you should be able to rely on the results of your home pregnancy tests (HPT) instead.

When a Blood Test Is Used

In routine pregnancies with healthy women, at-home urine tests are more than sufficient and effective. Blood tests are primarily used in doctors' offices, specifically, if there is a potential issue with the pregnancy or some other complicating factor (such as multiples), in which the greater sensitivity of the blood test is needed.

Blood tests may be ordered for higher risk pregnancies, during fertility treatments, when urine tests read negative but a period hasn't come, to confirm or rule out a possible miscarriage or multiples, and to diagnose a potential ectopic or tubal pregnancy, as well as due to other pregnancy complications.

Efficacy of Urine vs. Blood Pregnancy Tests

Urine tests are low-cost, painless, easy-to-use, can be done in the privacy of one's home, and are very accurate (in most scenarios), which is why they are the standard test used for most pregnancies.

A blood pregnancy test is warranted due to complicating factors. These tests are also very accurate, providing quick results that can give doctors more detailed information about your pregnancy.

Interpreting the Results

Normal results from a quantitative hCG blood pregnancy test would show that hCG levels are rising rapidly during the first trimester of pregnancy and then declining slightly after around 10 weeks. At around 16 weeks, the hCG levels stabilize for the remainder of the pregnancy. Abnormal results, on the other hand, can mean a variety of things.

Higher hCG Than Expected

A higher than normal level of hCG may indicate:

  • Infection or malignant tumors of the uterus
  • More than one fetus (for example, twins or triplets)
  • Non-cancerous tumors of the uterus
  • Ovarian cancer
  • Sometimes, just an indication of a normal pregnancy, farther along in gestation
  • Testicular cancer (in men)

Lower hCG Than Expected

Lower than normal levels of hCG may mean:

  • Ectopic pregnancy
  • Incomplete or complete miscarriage
  • Possible death of the fetus

Risks

There is very little risk associated with a blood pregnancy test. Aside from minor pain when the needle is injected, most people don't have any other side effects from having blood drawn. Occasionally, some people will have bruising at the site of the injection.

In rare cases, some people experience excessive bleeding, fainting, or infection from having blood drawn. Let your doctor know if you have ever had an issue with having blood drawn. 

A Word From Verywell

For most women, a urine-based, at-home pregnancy test will more than suffice to confirm pregnancy. Occasionally, a blood pregnancy test, either the qualitative or quantitative type, is needed to provide more information, particularly in medically complex situations. Both tests are safe, simple, and effective ways to know if you are pregnant. Blood tests are best when something else might be going on.

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