Function

• Blood serum tests done early in the first trimester of pregnancy may be performed to determine if there is a pregnancy. This type of screening, called a qualitative hCG test, tells you whether you are pregnant or not, and can detect pregnancy several days before urine based home pregnancy tests will be accurate. According to Healthopedia, a quantitative hCG test may be performed to measure the exact level of the pregnancy hormone hCG, or human chorionic gonadotropin, in order to date the pregnancy and make sure it is progressing normally. Blood tests are performed later in pregnancy to test for Rh antibodies, viruses, drugs, anemia and to screen for the likelihood of birth defects.
  
  

Procedure

• A blood sample is usually taken at a doctor's office from the inside of your arm below the elbow. The area is cleaned with antiseptic gauze, and a rubber tourniquet is tied tightly around the upper part of your arm. You may be asked to make a fist to enlarge the vein. A needle is inserted into the vein as the tourniquet is taken off, and you may be asked to open your hand. Drawn blood is placed in a vial for analysis and a cotton ball or bandage is placed over the needle mark.
  
  

Time Frame

• Blood tests will be sent to a laboratory to be analyzed; depending on where the lab is located and what information you are getting back, the procedure can take minutes or it can take weeks. You will probably get the results of a blood test to determine whether you are pregnant on the same day as your doctor's visit, while tests measuring quantitative hCG numbers may arrive the same day or take a few days to be processed. According to the American Pregnancy Association, results of an Alpha Fetoprotein Test or other triple screen tests meant to assess the likelihood of neural tube defects or chromosomal problems may take one to two weeks to be processed.
  
  

Benefits

• Blood serum screening tests can determine the likelihood of certain types of problems happening during your pregnancy. Screening of this type can also eliminate risk factors such as being Rh negative. According to CIGNA, if an Rh negative woman is treated early in her pregnancy with Rh immunoglobulin there is very little risk of fetal problems later on.
  
  

Warning

• Other than the discomfort of having your blood drawn, blood serum tests are not harmful to either you or your unborn child. The results of such tests, however, should not alone be used to make decisions about treatment. Confirm the results of blood serum tests through fetal ultrasound, additional blood tests or amniocentesis, as necessary, before treating any potential pregnancy or fetal complications.