What Blood Tests Do You Need During Pregnancy — and Why?

Pregnancy can be an exciting time — and also one filled with uncertainty. You might be caught off guard to realize that there are routine blood tests that are part of pregnancy checkups. Here we’ll review what blood tests are done during pregnancy, so you can show up to your visits knowing what to expect. 

What health issues do blood tests in pregnancy check for?

Blood tests in pregnancy look for conditions that can affect your health and your developing baby’s health. Since a pregnant woman and fetus share a blood supply, many health concerns can affect both mom and fetus. Blood tests in pregnancy are done to check for:

• Infectious diseases 

• Anemia 

• Blood disorders, such as sickle cell disease or thalassemia 

• Genetic conditions in the fetus and mother

• Blood type and the  Rhesus (Rh) factor

• Gestational diabetes

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Blood tests are done several times during pregnancy. Here we’ll break down exactly what your doctor or medical professional will be testing, and why these tests are important. 

Pregnancy complete blood count

A complete blood count is a blood test that looks at many different parts of your blood. This is often used as a screening test to look for a wide range of conditions. It measures:

• White blood cells: These are part of your immune system. Testing for the number and different subtypes can help identify problems with the immune system or infections.

• Red blood cells: These cells deliver oxygen from your lungs to the rest of the body. During pregnancy they also help deliver oxygen to your baby. A low red blood cell count can indicate anemia. 

• Platelets: These cell fragments help form clots and prevent bleeding. Low platelets during pregnancy can be due to gestational thrombocytopenia or other, less common pregnancy-related conditions. 

• Hemoglobin: Hemoglobin is an oxygen-carrying protein that’s found inside your red blood cells. It’s low if you have anemia from iron deficiency. A low hemoglobin level can also happen in conditions like sickle cell or thalassemia (more on this below). 

Blood test for sickle cell disease and thalassemia

Sickle cell disease and thalassemia are types of genetic disorders that can cause low hemoglobin levels. Most people with these conditions will be diagnosed in childhood with episodes of pain, fatigue, or jaundice. But other people are carriers for these conditions, meaning they carry the gene but don’t have any symptoms or problems. And because they don’t have symptoms, they may not know they’re carriers. 

You may think — no symptoms, no problem! Why does this matter? It matters because if you‘re a carrier for one of these conditions, and you have a baby with someone who’s also a carrier, then your child could be born with the condition. So knowing ahead of time will help your care team plan ahead to prevent complications for your baby. They may also recommend more frequent monitoring during your pregnancy.

The American College of Obstetrics and Gynecology (ACOG) recommends that every pregnant woman should be screened for these disorders, either before they get pregnant or at the first prenatal visit.

Your pregnancy care team may recommend one of the following tests:

• Hemoglobin electrophoresis: This is a blood test that will look specifically for disorders of red blood cells like sickle cell disease and thalassemia. 

• Molecular genetic screening: This is a test that uses your blood — or saliva — to test for DNA that’s associated with many different types of genetic disorders, including sickle cell and thalassemia.  

Blood type test

During pregnancy you’ll have a blood test to check what blood type you have. Your blood type depends on what kinds of protein are on your red blood cells. There are four main types of blood: A, B, AB, and O. It’s important to know what blood type you are in case you need a blood transfusion.  

Your blood type test will also include a test for Rh blood typing. That’s the + or - symbol that accompanies your blood type. The Rh factor is a protein that can exist on red blood cells. If you don’t carry the protein, but your baby does, it’s called Rh incompatibility. In this scenario, the mother’s immune system can react against the baby’s blood cells, which leads to health problems for the baby. 

All Rh negative mothers are at risk for Rh incompatibility if they have a Rh positive child. So if you’re Rhesus negative, you’ll need treatment with RhoGAM. This is a shot given at 28 weeks pregnancy and shortly after birth. It’s a safe and effective way to prevent complications from Rh incompatibility.  

Blood tests for infections

Some infections can be transmitted to a baby during pregnancy, even if you don’t have symptoms from the infection. But, medical treatment can lower the chance of transmitting these infections to the baby. 

Because of this, you’ll be offered blood tests to check for the following infections: 

• Human immunodeficiency virus (HIV)

• Hepatitis B

• Hepatitis C

• Syphilis

You’ll also have blood tests to see if you have immunity — through vaccination or past infection — to:

• Chickenpox

• Rubella

If your tests show that you don’t have immunity to these viruses, it means that you and your baby are at higher risk of getting these diseases. Both chickenpox and rubella can cause serious health problems for a pregnant mom and baby. Since the vaccines are live virus vaccines, they aren’t recommended to give during pregnancy. You’ll be advised to get vaccinated before your next pregnancy. And, if you’re exposed to these infections during this pregnancy, you should reach out to your pregnancy care team. 

If you have risk factors that place you at higher risk for having tuberculosis (TB), you should also be screened for TB. This can be done with a skin test or a blood test.

Glucose test

Your healthcare team will order a blood sugar test to screen for gestational diabetes. This is a type of diabetes that develops during pregnancy. This screening test is usually done after 24 weeks of gestation. If you have risk factors for diabetes, your healthcare professional might recommend doing this test earlier. 

The test is called a glucose challenge screening test. You start by drinking a liquid that contains glucose. One hour later, your blood will be drawn to measure the glucose level in your blood. 

If your blood sugar level is too high in the glucose challenge screening test, you’ll be asked to complete a 3-hour glucose tolerance test. Once again, you’ll drink a liquid that contains glucose. You’ll have your blood glucose measured before you drink the liquid, then every hour for 3 hours. 

Genetic testing

These tests are done to screen for certain genetic disorders in the fetus. ACOG recommends that all pregnant women should be offered genetic screening tests regardless of maternal age or risk level. 

If you decide to have genetic screening done, your healthcare professional will order one of the following two screening tests:  

• Genetic blood tests: Blood tests measure two substances — pregnancy associated plasma protein A (PAPP-A) and beta-human chorionic gonadotropic hormone (beta-HCG). Elevated levels could mean an increased risk of a genetic disorder.

• Cell-free DNA test: Cells in the placenta are released into the mother’s bloodstream after 10 weeks of pregnancy. So a blood draw from the mother for a cell-free DNA test can be tested for genetic disorders in the developing fetus. 

You may also be offered testing — through a blood test or saliva test — to see if you are a carrier for known genetic disorders. This is often called carrier screening. These are conditions in which you don’t have symptoms of a disease, but you carry a gene that you could pass on to your child. If you test positive as a carrier, you’ll need genetic counseling and more genetic tests may be recommended.  

When and how often is your blood tested during pregnancy?

Most people will have their blood tested at least three times during pregnancy: 

• First trimester: Healthcare professionals may perform blood counts, blood type, and infection screen. 

• Late second trimester: A glucose challenge is done — this may happen earlier if you have a higher risk for diabetes in pregnancy. 

• Genetic testing: This can happen in the first and/or second trimester, depending on the test. 

If any of your blood tests are abnormal, your obstetrician will likely order follow-up blood tests. So how often your blood work is checked will depend on your results and what conditions are being monitored. 

What other tests may be performed during pregnancy?

There are other routine screening tests during pregnancy that don’t involve a blood draw. 

Group B streptococcus swab 

Group B streptococcus (GBS) is a common bacteria that lives on the body and doesn’t usually cause health problems. But it can cause health problems for your baby if they get it from you during delivery. To prevent this, you’ll have a vaginal and rectal swab toward the end of your pregnancy, to test for GBS. If the test is positive, you’ll receive antibiotics during your delivery to protect your baby from infection. 

Urinalysis

Urine tests are common throughout pregnancy. These check for protein in your urine or signs of a urinary tract infection (UTI). 

Blood pressure checks

Blood pressure checks are also routine in pregnancy. These involve a quick and painless measurement of your blood pressure, at each office visit. Blood pressure checks screen for preeclampsia, a serious blood pressure disorder that can develop during pregnancy or soon after you give birth. 

Ultrasounds 

You should have at least one ultrasound exam during your pregnancy. This usually happens between 18 and 22 weeks of pregnancy. Many women also have an ultrasound in the first trimester. And some may have more regular ultrasounds during the pregnancy, especially if your care team is monitoring health issues. 

Why trust our experts?

Written by:

Karen Hovav, MD, FAAP

Karen Hovav, MD, FAAP, has more than 15 years of experience as an attending pediatrician in a variety of clinical settings. She has worked in a large academic center in an urban city, a small community hospital, a private practice, and an urgent care clinic.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. An experienced and dedicated pulmonologist and hospitalist, she spent a decade practicing and teaching clinical medicine at academic hospitals throughout London before transitioning to a career in health education and health technology.

Reviewed by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined her interests in clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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