Common Pregnancy Blood Tests and Pregnancy Screening Tests

When you’re expecting a baby, you know how important it is to keep up with your prenatal visits and to follow the advice of your healthcare team. One part of the pregnancy journey that can feel overwhelming is the set of decisions you’ll have to make about pregnancy blood tests and other screening tests available to you.

In this article, we will walk through the most common blood tests, including those that monitor your health, your baby’s health, and the progress of your pregnancy.

Be sure to discuss these tests during pregnancy with your doctor or midwife. Your healthcare provider will suggest several routine tests that are offered to all pregnant women. If you are at higher risk of certain conditions because of your health history, they may also recommend advanced testing to identify risk factors.

It’s important to note that screening tests are optional. While some women prefer to undergo screening and diagnostic testing for genetic issues, others prefer not to pursue this testing in their pregnancy. Be sure to discuss all your questions and health concerns about screening options with your doctor. Keeping an open dialogue with your healthcare team will help you stay informed about all your risks and testing options.

Common Blood Test Screenings

During your pregnancy, there are two main types of tests: screening and diagnostic tests. Screening tests are noninvasive tests that can help identify pregnancies that face a higher than average risk of a certain condition or outcome. Diagnostic tests are used to confirm the presence of a certain condition. Your doctor may recommend these tests when the results of screening tests show an increased health risk to women or their babies.

Human Chorionic Gonadotropin

Human chorionic gonadotropin (hCG) is commonly measured as part of a first trimester blood test. HCG is a hormone that is produced by the placenta during pregnancy. Abnormal levels of hCG in pregnancy can indicate a higher risk of genetic problems. The hCG test can also help your healthcare provider determine the gestational age of your baby and identify potential health problems, such as an ectopic pregnancy or a miscarriage.

Pregnancy-associated Plasma Protein A

Pregnancy-associated plasma protein A (PAPP-A) is a protein that the placenta makes during pregnancy. Together with hCG, A PAPP-A test is a first trimester screening typically done between weeks 11 and 13. The testing screens for chromosomal abnormalities—such as Down syndrome, as well as other pregnancy conditions like preeclampsia.

Alpha-fetoprotein (AFP)

Alpha-fetoprotein (AFP) is a protein that comes from the baby’s liver and circulates in the mother’s blood. AFP levels are helpful in screening for neural tube defects like spina bifida, and genetic issues like Down syndrome. This prenatal screening is usually done between weeks 15 and 20 of pregnancy. If the results are abnormal, your doctor will recommend further testing to diagnose possible problems.

Blood Tests for Infectious Diseases

There are several blood tests that are given early in pregnancy to diagnose infections that may affect your baby. These tests include:

• Human Immunodeficiency virus (HIV)
• Rubella (German measles)
• Syphilis
• Hepatitis B
• Hepatitis C
• Varicella
• Cytomegalovirus

If you have any of these infectious diseases, your doctor will treat them so you can have a healthy pregnancy and delivery. For more information on the diseases that can affect a pregnancy or a healthy birth, check out this resource from the American College of Obstetricians and Gynecologists.

Full Blood Count

A full blood count, also called complete blood count or full blood examination, measures the components of the blood, including red and white blood cells and platelets. This count gives important health information about whether you may have anemia, a condition where there are not enough healthy red blood cells to transport oxygen to cells. This screening is typically performed in the first trimester, but may be repeated throughout your pregnancy if needed.

Blood Type

It’s important to have a simple test to tell your doctor which blood type you are. This information will be useful in case you need a blood transfusion at some point during your pregnancy or delivery. There are four blood type groups: A, B, O, and AB.

Rhesus Status Testing

Part of your blood type testing will include a test for Rhesus status, or Rh status. You can be either Rh positive or Rh negative. If you are Rh positive, no treatment will be needed. If you are Rh negative and your baby is Rh positive, your body may make antibodies which will not hurt your first baby, but which can be harmful for later pregnancies. If you are found to be Rh negative, your doctor will provide treatments to prevent your body from producing these antibodies.

Second Trimester Maternal Serum Screen

A blood test in the second trimester, called the Maternal Serum Screen or Quad Screen, helps doctors identify if you are at a higher risk of having a baby with certain birth defects, like neural tube defects or Down syndrome. This second trimester screening measures levels of AFP, hCG, estriol, and inhibin-A in the blood.

PreTRM Test for Preterm Birth Risk Management

The PreTRM Test is a blood test that your doctor can order during weeks 18-20 of your pregnancy. This test measures the level of two proteins in your blood: Insulin-like growth factor binding protein (IBP4) and sex hormone binding globulin (SHBG). Scientists have discovered that the ratio of these proteins in the blood of pregnant women can provide information on each pregnancy’s individual risk of ending in spontaneous preterm birth. With the information from the PreTRM Test, doctors and mothers can work together to adjust pregnancy care plans as needed. For more information on the PreTRM Test, see PreTRM FAQs for Moms.

Genetic Conditions Screening Tests

Carrier tests are screening tests that check a sample of your blood or saliva to see whether you may be a carrier of certain genetic conditions. Cell-free fetal DNA testing is a way to check your blood for your baby’s DNA to screen for certain genetic conditions. If this pregnancy screening is positive, your doctor may offer you diagnostic tests to confirm the presence of this genetic condition. The March of Dimes has great resources to learn more about genes, chromosomes, and testing for chromosomal abnormalities during pregnancy.

Some of the genetic disorders that can be identified through pregnancy screening and diagnostic tests are:

• Down syndrome. Associated with a range of physical and cognitive features, including developmental delays and heart defects.
• Cystic fibrosis. Affects the respiratory, digestive, and reproductive systems.
• Duchenne muscular dystrophy. Characterized by progressive muscle weakness.
• Hemophilia A. Caused by a lack in blood clotting factor that can result in prolonged bleeding.
• Polycystic kidney disease. Causes growths in the kidneys, which can lead to poor kidney function.
• Sickle cell disease. Affects red blood cells, causing them to form sickle shapes, leading to blocked blood vessels and other issues.
• Tay-Sachs disease. Causes damage to nerve cells, leading to developmental delays, loss of motor skills, and early death.
• Thalassemia. Causes abnormal production of hemoglobin, an important blood protein.
• Edwards syndrome. Also known as Trisomy 18, a rare disorder that affects growth and development.
• Patau syndrome. Also known as Trisomy 13, a rare disorder that affects the development of the face, brain, and heart.

Other Common Pregnancy Tests

Ultrasound

Ultrasounds are useful in giving your healthcare team pictures and measurements of your baby inside the womb. You may receive several ultrasound tests, including a transvaginal ultrasound, over the course of your pregnancy, to confirm the gestational age, screen for possible birth defects, identify your baby’s sex, measure the cervix, and track the health of the baby. For a detailed look at the types of ultrasounds used during pregnancy, check out our blog about prenatal tests.

Fetal Monitoring

At every prenatal visit, your healthcare provider will use a fetoscope (a type of stethoscope) to measure your baby’s heartbeat. When you are in labor, you may also have external fetal heart rate monitoring that measures both the baby’s heartbeat and the strength and timing of your contractions. In this type of testing, doctors strap a sensor to your belly that sends signals to a monitor.

In some cases, doctors may need more detailed information about the baby’s heart rate. If your water has broken and they need this health data, they may use internal fetal heart rate monitoring. In this test, your doctor will place a thin wire called an electrode through the vagina onto the baby’s scalp. For more information on how doctors measure contractions and fetal heart rate, read our blog about monitoring contractions.

Glucose Challenge and Glucose Tolerance Test

Your healthcare team may give you a glucose challenge test between weeks 24 and 28 to see how your body processes sugar. For this testing, you’ll drink a sugar solution and your blood will be measured at regular intervals to test for problems. If the results of this test are abnormal, your doctor may give you a glucose tolerance test to see if you have gestational diabetes. If you are diagnosed with gestational diabetes, you and your doctor can work together to treat it effectively and maintain a healthy pregnancy. The American Diabetes Association has excellent educational resources about how gestational diabetes affects pregnancy.

Group B Streptococcus Screening

Group B strep (GBS) is a bacterium found in the lower genital tract. Although it is usually harmless to adults, the bacteria can be dangerous when passed on to babies during delivery. This screening test involves a swab of the vagina and rectum. If a GBS infection is detected in the sample, you will get treated before delivery to protect your baby.

Less Common Prenatal Tests

Amniocentesis

In cases where results of other screening tests have an abnormal result, doctors may recommend amniocentesis to identify certain health conditions. This test involves inserting a thin needle through the belly to collect a small amount of amniotic fluid from the amniotic sac. The test is done with the help of ultrasound and is generally considered to be safe for both mom and baby. However, it does carry a small risk of complications, including infection, bleeding, and miscarriage.

Chorionic Villus Sampling (CVS)

Chorionic villus sampling, or CVS, is a diagnostic test your doctor may offer if your pregnancy is in a high risk category for certain genetic conditions. This involves taking a sample of tissue from the placenta. It is not offered to all pregnant women, as it raises the risk of miscarriage.

Percutaneous Umbilical Blood Sampling

Percutaneous umbilical blood sampling is also known as cordocentesis or fetal blood sampling. It is performed during the second or third trimester if there are concerns about the health of the fetus or to diagnose certain genetic disorders or infections. This blood test involves inserting an ultrasound-guided needle through the mother’s belly to collect a blood sample from the umbilical cord. While it is generally considered to be safe, it does carry some risks, including injury to the developing baby.

Pregnancy blood tests are an important part of your prenatal care. It’s important to understand the purpose of each test during pregnancy, and to know that you always have the choice to undergo screening. Be sure to discuss all your testing options with your healthcare provider.

FAQs about common Prenatal Tests

How early can Down syndrome be detected?

Screening for Down syndrome can be done as early as the first semester of pregnancy with ultrasound and blood tests. It can also happen in the second semester with a Quad Screen. If the results of screening are abnormal, more invasive tests like amniocentesis or chorionic villus sampling can diagnose the genetic condition.

What two blood types are not compatible for pregnancy?

Problems can happen when a mother is Rh negative, and the baby is Rh positive. In a first pregnancy, there is no risk to the baby. But in subsequent pregnancies, the mismatch can cause problems for the baby. There are treatments available to prevent the mother from creating antibodies that can cause harm to the baby when blood testing identifies the risks.

There is also a situation where a mother has Type O blood, and a baby has A, B, or AB blood. While the mother’s body will also make antibodies to the baby’s blood type, they are too large to cross the placental barrier and cause harm to the baby. In rare cases where a delivery causes a risk to the baby, doctors can give the mother a blood transfusion to solve the problem.

How long after implantation does hCG rise?

HCG levels vary across pregnancies. In general, however, hCG levels begin to rise between six and 12 days after implantation.

HCG can be detected in either blood or urine. However, a blood test is more accurate because it can detect smaller amounts of hCG.

What blood tests are done in the first trimester of pregnancy?

During your first prenatal visits, you will be tested for blood type and Rh factor, complete blood count to screen for anemia (low iron), and infectious disease testing for rubella, hepatitis B, syphilis, HIV, and other sexually transmitted diseases.