Image of some blood tests

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

How is a blood test performed?

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

When are blood tests performed?

A blood test should be expected during your first prenatal exam.  Additional blood testing may be requested to monitor potential complications, such as anemia or diagnosis of possible infections, such as toxoplasmosis.

What does a blood test look for?

A blood test is used to assess 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 assess whether you are immune to rubella, to see if you have a sexually transmitted disease, or to see if you have a toxoplasmosis infection. A blood test is also part of the Triple Screen Test.

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

What can blood test results tell me?

Blood Type: The blood test will diagnose your blood type. You will either be A, B, AB or O.

Rh Factor:The blood test will also reveal whether you are Rh negative or Rh positive. If you do not have the Rh antigen in your blood, then you are Rh negative.  If you do have it, then you are Rh positive. This test is important because problems may arise if the mother’s blood does not have the Rh factor and the baby’s blood does.

Glucose Levels: The blood test is used to measure the body’s ability to metabolize sugar and screen for gestational diabetes. If your glucose level is between 130 to 140 milligrams per deciliter of blood, then your healthcare provider will request a glucose tolerance test.

Iron Levels: The blood test will determine if you have iron deficiencies in your blood. Even if your blood is low in iron, it does not mean you are anemic, but it does make you more susceptible to anemia. If your levels are low, your healthcare provider may prescribe iron tablets or injections.

Hemoglobin Levels: The blood test will identify the level of hemoglobin, which is the oxygen-carrying power of your red blood cells. The expected level is between 12 to 14 grams. Treatment for anemia will be prescribed if your level falls below 10 grams.

Sexually Transmitted Diseases: A blood test is a diagnostic test used to determine whether you have syphilis, hepatitis B, or HIV.

Rubella (German measles): The results of the blood test will determine if you have antibodies for rubella and whether or not you are immune.

ToxoplasmosisThe results of the blood test will determine if you have the toxoplasmosis infection. Toxoplasmosis is harmless to you, but it may cross the placenta and cause harm to the baby.

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

Outside the discomfort of having blood drawn, a blood test poses no risks to the mother or developing fetus. This test is a routine part of your prenatal care.

Compiled using information from the following sources:

1. Nemours Foundation

2. William’s Obstetrics Twenty-Second Ed. Cunningham, F. Gary, et al, Ch. 8.