What Is a Pregnancy Blood Test?

A pregnancy blood test can confirm whether or not a person is pregnant by checking for the presence of human chorionic gonadotropin (hCG), a hormone that the body produces during pregnancy.

Pregnancy blood tests are done at a healthcare provider's office or medical laboratory. The process involves drawing a blood sample from the vein using a small needle.

Your healthcare provider may recommend a pregnancy blood test as a follow-up to an at-home urine test or if there are other special circumstances, such as ongoing fertility treatments or a potential pregnancy issue.

Types

Healthcare providers use two different types of pregnancy blood tests to check levels of hCG in the body.

A qualitative pregnancy blood test tells you whether hCG is present and has roughly the same accuracy as an at-home urine pregnancy test. This test is done when a simple “yes, you’re pregnant” or “no, you’re not pregnant” answer is needed.

A quantitative pregnancy blood test (also known as a beta hCG test) measures exactly how much hCG is in your blood, providing more information than simply whether or not you are pregnant. This test is highly sensitive, detecting even trace amounts of hCG.

A quantitative pregnancy blood test can help your healthcare provider determine how many weeks you are pregnant. They can also use it in combination with other tests, like ultrasound, to diagnose pregnancy loss or other complications.

Purpose

Pregnancy blood tests are usually done in special circumstances, like when there may be infertility issues, a high-risk pregnancy, or other potential complications. They’re also sometimes recommended as a follow-up to confirm home pregnancy test results or compare hCG levels during various points in the pregnancy.

In addition to confirming a pregnancy, blood pregnancy tests can provide information to the clinician that may help in screening for or determining:

• A “multiples” pregnancy (twins, triplets, or more)
• The age of the fetus
• An abnormal pregnancy, such as an ectopic pregnancy (when a fertilized egg implants outside of the uterus) or molar pregnancy (when a mass of tissue grows inside of the uterus instead of a placenta)
• A miscarriage
• Down syndrome

In some cases, pregnancy blood tests can also be used to screen for pregnancy ahead of certain medical procedures that could be harmful to a fetus, like magnetic resonance imaging (MRI) or X-ray.

Importance

A pregnancy blood test is more sensitive than a urine test, meaning it can detect a pregnancy earlier and measure hCG levels. In fact, a pregnancy blood test can sometimes detect pregnancy even before you’ve missed a period. The test can usually detect hCG as soon as eight days after conception.

In normal pregnancies, hCG levels rise rapidly in the first trimester before they start to decline. So if a pregnancy blood test reveals that your hCG levels are not rising as they should, it may be an indication that there’s an issue with the pregnancy.

On the other hand, an extremely high hCG level could suggest that the person is carrying twins or could have an abnormal pregnancy. In these situations, your healthcare provider will discuss the meaning of the results with you and may order repeat tests every few days to get a better read on the hCG levels.

Risks

Pregnancy blood tests are considered a safe, simple, and effective way to determine hCG levels in the body, and there’s very little risk with having one done. Aside from any minor pain or discomfort for a few seconds when the needle is injected, most people don’t experience other side effects from having blood drawn.

Like any blood draw, it’s possible to feel lightheaded or dizzy. In more rare cases, there’s a chance for fainting, excessive bleeding, and infection or bruising at the site where the needle went in.

The size of veins differs from person to person, so getting a blood sample could be more difficult or require more attempts to locate a vein for some people. Let your healthcare professional know if you have ever had issues with having your blood drawn so that they can try to make the process as quick and painless as possible.

Accuracy

Pregnancy blood tests can be 99% accurate. But just like with an at-home urine pregnancy test, there’s still a chance you can end up with an inaccurate result, like one that says you’re not pregnant when you really are (a false negative) or one that finds you’re pregnant when you aren’t (a false positive).

A common reason for an inaccurate test result is having your blood drawn too early, before your hCG levels have had a chance to rise. Another example is having hCG detected in your blood for another reason, such as taking the test shortly after taking fertility drugs containing hCG, or in cases of certain medical issues.

Every person’s body and pregnancy are different. If you believe that you received an inaccurate test result from testing too soon, talk to your healthcare professional about repeating the test in another 48 to 72 hours.

A Word From Verywell

While pregnancy blood tests can be useful and informative, remember that they’re just one way healthcare professionals gather information about a pregnancy. If you have concerns about your results or hCG levels, talk to your healthcare professional about further hCG testing and other diagnostic tools that may be helpful.

An early ultrasound can be done during the first trimester to provide you and your healthcare provider with additional insight into the pregnancy along with the hCG numbers.