Blood-Based Pregnancy Tests

Taking blood for a pregnancy test

Although home pregnancy tests are more accurate than ever before, a blood-based pregnancy test is typically performed by health practitioners to determine pregnancy. In addition, there are other common blood tests performed during pregnancy.

Urine Versus Blood-Based Pregnancy Tests

There are typically two ways to detect the HCG levels in a woman's body to confirm or deny pregnancy. Many urine-based pregnancy tests are sold over the counter. These tests measure the amount of HCG that is present in the urine at the time of the test.

Blood-based pregnancy tests also measure the level of HCG present in a woman's body, but these are typically performed at a doctor's office or health clinic. Even if a woman has taken a home pregnancy test, a blood-based test is usually administered to confirm the pregnancy. It can also be scheduled if a woman suspects she is pregnant and has not yet taken an at-home test. A blood pregnancy test typically picks up the hormones earlier than a urine based test.

How the Blood Tests Work

Qualitative vs. Quantitative Tests

There are two different types of blood tests to check for pregnancy: qualitative and quantitative. A qualitative test can determine exactly what amount of HCG is present in the blood, while a qualitative test simply determines whether any HCG is present.A qualitative test may be performed to initially confirm the pregnancy. A quantitative test may be performed ensure that the HCG levels are increasing normally and identify potential problems. It is not uncommon for a woman to receive several quantitative tests in early pregnancy.

How the Test is Performed

The test is performed by a nurse or lab technician drawing blood from a vein in the arm, typically the forearm or hand. The blood is collected in a syringe or vial. The test may be performed at you practitioner's facility or at a medical lab at a separate facility. The results of the test are sent to the appropriate section of the lab for testing and your doctor will receive the results. The time it takes to receive the results depend on a variety of factors, in some cases the results will be available the same day, while in other cases you may have to wait several days. Talk to your physician to find out what is common for his or her office.

Common Questions About Blood Pregnancy Tests

Is there any way that a blood pregnancy test can be wrong?

Although the blood-based pregnancy test is highly accurate, there are certain circumstances and conditions which can affect its results and possibly give an incorrect reading. This includes:

  • Situations with women who are using fertility drugs. The test may show a false positive for pregnancy when it is, in fact, detecting the HCG hormones present from the treatments.
  • The test is performed too soon. Although uncommon for a blood test, it's possible the levels may be too low to detect. This is more common in urine-based tests since a blood test can detect pregnancy hormones six to eight days after ovulation.

Why do I need the blood test?

If you've already taken a home pregnancy test and it is positive, you will almost always still need to take an initial blood pregnancy test. The reasons for this include:

  • Your practitioner can confirm the pregnancy and begin your prenatal care.
  • Your practitioner can determine whether the pregnancy is progressing normally and discuss any issues that may arise with you.
  • You may need confirmation of the pregnancy for public health care or other publicly funded programs such as WIC.

Other Blood Tests Performed During Pregnancy

In addition to checking HCG levels to determine pregnancy and its normal progression, there are a number of other pregnancy blood tests that may be performed during pregnancy.

  • Pregnancy-Associated Plasma Protein Screening (PAPP-A): This blood test measures the levels of a certain protein produced by the placenta. Unusual levels may identify chromosome abnormalities.
  • Alpha-Fetoprotein Screening (AFP): This blood test is performed during the second trimester of pregnancy. Results can signal:
    • Presence of twins
    • More accurate due dates
    • Possible neural tube defects (such as spina bifida) and Down's Syndrome
  • Genetic Screening: When there is a family history of genetic disorders, genetic screening tests may be performed. These are done by blood tests and other methods.
  • Blood tests are also performed during pregnancy to check:
    • Mother's blood type/ RH factor
    • Presence of any sexually transmitted diseases
    • Anemia
    • Gestational diabetes
    • Presence of antibodies for diseases that could be dangerous in pregnancy, such as chicken pox and rubella

Speak with Your Doctor

A blood test is the most accurate way to confirm pregnancy, and tests following the initial determination can help doctors monitor the health of you and your child. Always ask your doctor or nurse about any tests performed if you need more information or have any concerns about any blood test.

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Blood-Based Pregnancy Tests