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PreNatal Tests – What Do They Mean?

Throughout your pregnancy, you may have tests performed to screen for certain medical conditions that can affect either you or your baby. The following is a list of the tests with an explanation.

Pre-Conceptually OR at Your First OB Visit

Complete Blood Count (CBC)

A blood test to provide a count of red and white blood cells and platelets.

  • Red blood cells are responsible for carrying oxygen to your organs and to your baby. If you do not have enough red cells (a condition called anemia), you may become excessively tired and your baby may not be getting the oxygen she/he needs. Sometime further testing is needed. Treatment for anemia is generally iron supplements.
  • White blood cells fight infection and disease. An increased or decreased number alerts us to the need for further testing.
  • Platelets are responsible for blood clotting. Certain abnormalities in platelets may never cause symptoms but can lead to problems during delivery. An abnormal value may indicate the need for further testing.

Type and Screen

A blood test to determine your blood type and the presence of any unusual antigens (proteins on the red blood cells). The RH Factor is the most common antigen that is either present (Rh+) to absent (Rh-).

If a mother is Rh- and the father is Rh+, there is a chance the baby will be Rh+. This can cause problems if there is a crossover of the baby's Rh+ cells into the mother's blood stream. These "foreign" cells may lead to the production of a substance in the mothers blood (antibody) which actually attacks fetal red cells and may cause many problems in the baby; including heart failure, anemia, enlarged liver and spleen, jaundice (yellowing of the skin), and even still births.

If you are Rh-, you will need to have an injection of Rhogam automatically at 28 weeks or anytime you bleed during your pregnancy; and possibly after giving birth. This injection will prevent your body from making any of the potentially harmful antibodies.

You are also tested for other antibodies similar to those produced against the Rh factor, whose presence can also affect the baby.


A blood test to determine whether you have immunity to Rubella (German Measles). If a woman has not been immunized by the Rubella vaccine or contracted Rubella herself, she is at risk for getting the disease if exposed. Exposure during pregnancy is associated with numerous birth defects including mental retardation, deafness, cataracts and heart defects. If you are not immune, you will need to avoid contact with persons who have the disease. You will be offered vaccination after you baby is born.


A blood test for the sexually transmitted disease Syphilis. This disease can be passed to the baby during pregnancy and can cause certain birth defects including still births, bone and teeth defects and brain damage. Treatment for Syphilis is antibiotics.

Hepatitis B

A blood test for the viral liver infection, Hepatitis B. This condition poses a problem for the baby after delivery. If you test positive for this virus, your baby will receive immunization and special handling after birth.


A test of your urine which indicates exposure to the sexually transmitted disease Chlamydia. This disease can cause pneumonia and eye infections in babies. Treatment for Chlamydia is antibiotics.

Urine Culture

A test of your urine to determine if it is infected with bacteria that could cause urinary tract infection (UTI). Urinary tract infections are more common in pregnancy due to anatomical changes of the urinary tract and may cause no recognizable symptoms. Treatment for bacteria in the urine is antibiotics.

Genetic Testing

Such as Cystic Fibrosis or Tay-Sachs disease. Your risk of carrying the gene for some diseases depends on your inherited ethnicity. Your risks will be reviewed and recommendations for testing made. These tests will require you to sign a consent form informing you of the limitations and uses of testing.


A blood test for the presence of HIV (Human immunodeficiency virus), the causative agent for AIDS (Acquired immune deficiency syndrome) . This test is optional and voluntary and can be obtained only after you sign a consent. We encourage all women to consider this testing option as 25 percent of women who are HIV-positive and untreated will pass this disease to their babies; and because treatments like AZT can dramatically lower transmission rates. This will be fully explained to you at your first visit.


A blood test for the presence of active or past infection with the parasite Toxoplasmosis. Infection with this parasite can cause mild to severe congenital defects, and is contracted by exposure to undercooked red meats, garden soils, and cat feces. If you have exposure to these risk factors you will be tested for Toxoplasmosis. If not, we will discuss ways to avoid exposure during pregnancy.


A blood test for the presence of active or past viral infection with the organism that causes Fifth's disease. This disease is contracted by exposure to persons (most commonly young children) who have Fifth's disease. Exposure to this virus during pregnancy can cause fetal anemia or heart failure and even miscarriage. If you have extensive contact with groups of young children, you will be tested for the presence of this virus. We will discuss ways to avoid exposure during pregnancy.


A blood test for the presence of past infection with, or immunization to, the virus that causes chickenpox. If you have had chickenpox in the past you are immune to the disease and need not be tested. If you are unaware of past disease and have not been vaccinated, you will receive this test. Varicella infection during pregnancy can cause numerous birth defects and may increase the risk of miscarriage. You may be vaccinated against varicella after your baby is born.

Second Visit

During this visit you may have a complete physical examination, including a pelvic exam, and the following tests:

Pap Smear

A gentle scraping of the cervix which yields cells that are screened for cervical cancer. During pregnancy, a soft brush is used which rarely causes bleeding, although a small amount of spotting is normal. If an abnormality is found, an additional test called colposcopy will need to be performed.

Gonorrhea Culture

A test of cervical fluid for the bacteria, which causes the sexually transmitted disease Gonorrhea. Transmission of Gonorrhea can occur to the baby and cause blindness. Treatment for this infection is antibiotics.

24-28 Weeks

Glucose Test

This blood test screens you for the risk of gestational diabetes. You will be asked to drink a sweet tasting beverage called Glucola, and have your blood drawn one-hour later. An abnormal result on this test does not necessarily mean that you have diabetes. For confirmation another test called a Glucose Tolerance Test may need to be performed. This involves fasting overnight, having your blood drawn, drinking more Glucola and then having your blood drawn at 1, 2, 3-hour intervals. Gestational diabetes may lead to complications in pregnancy and with the baby. If you have diabetes, you will be evaluated by a specialist and begin a diet, exercise, and testing program developed for you.

36 Weeks

Group B Strep

Vaginal and rectal cultures that test for the presence of Group B Strep, a common non-sexually transmitted bacterium found in 30 percent of women. Babies exposed to this bacterium during birth may develop life-threatening illness unless the mother is treated. If you are positive for this bacterium you will be given IV antibiotics while you are in labor or as soon as your membranes rupture.

Contact Information

Department of Obstetrics and Gynecology
Beth Israel Deaconess Medical Center
East Campus
330 Brookline Avenue
Boston, MA 02215