Blood test in pregnancy

A blood test is a routine test used by your doctor as part of your prenatal care. Although blood tests are used for pregnancy screening, the following describes how blood tests are used as part of antenatal care.

How is a blood test done?

Your doctor will take a small sample of blood, usually from a vein in your arm. The blood sample will be sent to a laboratory for analysis.

When are blood tests done?

A blood test should be expected at your first prenatal checkup. Additional blood tests may be ordered to monitor for possible complications, such as anemia, or to diagnose possible infections, such as toxoplasmosis.

What does a blood test show?

A blood test is used to evaluate blood type (A, B, AB, and O), Rh factor (Rh positive or negative), glucose, iron, and hemoglobin levels. A blood test is also used to see if you are immune to rubella, to find out if you have a sexually transmitted disease, or to find out if you have a toxoplasmosis infection. The blood test is also part of the triple screening test.

Blood tests can also be used to diagnose certain genetic disorders such as familial hypercholesterolemia, cystic fibrosis, sickle cell anemia, thalassemia, and Tay-Sachs disease.

What can my blood test results tell me?

Blood Type: A blood test will determine your blood type. You will either be A, B, AB or O.
Rh factor: A blood test will also show whether you are Rh negative or Rh positive. If you do not have the Rh antigen in your blood, you are Rh negative. If you have it, then you are Rh-positive. This test is important because problems can arise if the mother's blood does not have the Rh factor but the baby does.
Glucose levels: A blood test is used to measure the body's ability to process sugar and to detect gestational diabetes. If your glucose level is between 130 and 140 milligrams per deciliter of blood, your doctor will order a glucose tolerance test.
Iron levels: A blood test will determine if you have an iron deficiency in your blood. Even if your blood is low in iron, it doesn't mean you have anemia, but it does make you more susceptible to anemia. If your levels are low, your doctor may prescribe iron tablets or injections.
Hemoglobin level: A blood test will determine the level of hemoglobin, which is the oxygen-carrying capacity of red blood cells. The expected level is 12 to 14 grams. You will be treated for anemia if your levels fall below 10 grams.
Sexually transmitted diseases: A blood test is a diagnostic test used to determine if you have syphilis, hepatitis B or HIV.
Rubella (German measles): The results of the blood test will determine if you have rubella antibodies and if you are immune.
Toxoplasmosis: The results of the blood test will determine if you have a toxoplasmosis infection. Toxoplasmosis is harmless to you, but it can cross the placenta and harm the baby.

What are the risks and side effects of a blood test for the mother or baby?

Apart from the discomfort of drawing blood, the blood test poses no risk to the mother or the developing fetus. This test is an integral part of your prenatal care.