Pregnancy Blood Test

This page will help you understand some of the blood tests related to pregnancy.

Finding Out If You're Pregnant: Pregnancy Blood Test vs. Urine Test

Pregnancy tests look for a hormone called human chorionic gonadotropin (HCG), which is associated with pregnancy. Pregnancy urine tests are very accurate. If you’re just trying to find out if you’re pregnant, most of the time a urine test is all you need.

A pregnancy blood test can measure not just the presence of HCG, but the amount of it in your blood. It can also detect lower levels of HCG than a urine test can. It can confirm pregnancy as much as two weeks before a urine test.

Levels of HCG in your blood rise in a predictable way throughout your first trimester. If the pregnancy is normal, HCG can be used to help determine the age of the fetus. Abnormal HCG levels can signal a problem with the pregnancy.

Routine Prenatal Blood Tests

At your first prenatal appointment, your doctor or midwife will probably want you to have blood tests for the following:

• Infection. Certain sexually transmitted infections can be very harmful to the baby. Pregnant women are usually checked for Hepatitis B and syphilis. Your doctor may check for other infections, too, including HIV.
• Antibodies to German measles (also called rubella) and chickenpox. These infections can cause birth defects. If you have the antibodies, it means you’ve had either the vaccine or the illness. You should now be immune to both diseases.
• Anemia. Being anemic means you have a shortage of red blood cells, often due to not getting enough iron in your diet. Anemia can make you feel run-down and tired. It may also put you at risk of having a premature baby.
• Blood type, including Rh factor. If you are Rh-negative and your partner is Rh-positive, you may need treatment to protect your baby from a blood problem.
• Cystic Fibrosis gene test. Cystic Fibrosis (CF) is a genetic lung disease. If you and your partner are both carriers of the gene, your baby could be at risk. If you’re not offered this test, ask if you should have it.

Depending on your genetic background, you and your partner may also want to have a pregnancy blood test for genetic problems such as sickle cell disease or Tay-Sachs.

The Triple Screen (or Quadruple Screen)

The triple screen is a pregnancy blood test that’s done around the 15th to 18th week. It checks for Down’s syndrome and also certain neurological defects. It’s called a triple screen because it looks for three substances in the blood: alpha-feto protein (AFP), human chorionic gonadotropin (HCG), and unconjugated estriol. Some versions of the test also include inhibin-A, which seems to make the test for Down's syndrome more accurate. In that case, the test is called a quadruple screen.

The triple or quadruple screen does not tell you if your baby definitely has a problem. If it is positive, you may need additional tests, such as ultrasound or amniocentesis, to find out if anything is really wrong. A negative test is reassuring, but it’s not a guarantee. For example, a quadruple screen catches Down’s syndrome only about 75 to 80% of the time.

The Glucose Tolerance Test

Near the end of your second trimester, you will probably be given a glucose tolerance test, which checks for gestational diabetes. Pregnant women are at risk of developing this special kind of diabetes, which comes on during the pregnancy and goes away afterward. You’ll be given a sweet liquid to drink. About an hour later, you’ll have blood drawn to check the glucose level.

Other Tests

During your pregnancy, blood tests may be needed for other reasons. You doctor or midwife may need to check your kidney or liver function, re-check you for anemia, or look for other problems.

You can also expect to have other kinds of routine tests, including urine tests, ultrasounds, and gynecological exams.

Talk with your health care provider to find out exactly what tests you need.