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Tests During Pregnancy: Tests for Women at Risk

Screening Tests

In addition to the standard prenatal visit tests, women who are at higher risk for certain conditions should undergo further screening tests. Pregnant women who have lived in regions where tuberculosis is common should have a tuberculin skin test at their first prenatal visit; women who are at risk for diabetes should undergo a glucose tolerance test; and women who are at risk for ectopic pregnancy or miscarriage should have their blood tested for levels of beta-hCG hormone.

Screening for Tuberculosis

The tuberculin skin test is administered by injecting a small amount of fluid (the tuberculin antigen) under the skin of the forearm. Two to three days later, the site of the injection must be checked by your doctor or nurse for any reaction. If a bump has developed and measures more than 10 mm in a high-risk area (or 15 mm in a low-risk area), the test is interpreted as positive. A positive skin test reaction indicates that you have been exposed to tuberculosis at some time during your life. (Skin test results are accurate even when you received the BCG vaccination against tuberculosis as a child-as long as it has been 10 years since your last BCG injection. Although used worldwide, the BCG vaccine is not routinely administered to patients in the U.S.)

If your skin test is positive, you will need a chest x-ray to rule out the possibility of active tuberculosis. A chest x-ray is safe during pregnancy when you wear a lead shield over your abdomen-radiation exposure to the fetus is minimal and the benefits of ensuring that you do not have tuberculosis during pregnancy outweigh any risks associated with the x-ray.

If your chest x-ray is normal, you are healthy, and you are under 35 years of age, you should receive a course of treatment with isoniazid (Nydrazid) after pregnancy to prevent the development of active disease.

If your chest x-ray shows any evidence of tuberculosis, your sputum (mucus coughed up from your lungs) should be tested for tuberculosis and your provider should send you for immediate evaluation by a pulmonologist (a doctor specializing in conditions of the lung) or infectious disease specialist. If your sputum is positive or your chest x-ray is highly suspicious, your provider will most likely want to treat you for tuberculosis during pregnancy so that your baby is not born with tuberculosis and does not contract tuberculosis after birth.

Screening for Diabetes

Risk Factors for Gestational Diabetes

  • Previous delivery of a baby heavier than 9 pounds at birth (macrosomia)
  • History of gestational diabetes
  • Family history of diabetes
  • Advanced maternal age (older than 35 years)
  • Obesity
  • Certain ethnicities (Pima Indians)
  • History of unexplained stillborn baby

If you have any risk factors for developing diabetes during pregnancy (gestational diabetes), your provider will have you take a one-hour glucose tolerance test during your first prenatal visit.

The one-hour glucose tolerance test involves drinking a cup of a flavored sugar solution (containing 50 grams of sugar) and having your blood drawn one hour later to check your blood sugar (glucose) level.

  • If the results are normal (glucose level less than 140 mg/dL), the test will be repeated between 24 and 28 weeks gestation to check for any changes.
  • If the test is abnormal, you should undergo a three-hour oral glucose tolerance test (OGTT) to evaluate your metabolism of carbohydrates.

Three-Hour Glucose Tolerance Test

  • You will need to be on a special high carbohydrate diet for three days before the test is performed.
  • On the morning of the test, you will go to the office or hospital after an 8-hour, overnight fast. You will have your blood drawn before you have anything to eat or drink.
  • You will then drink a cup of flavored sugar solution (containing 100 grams of sugar), and your blood sugar (glucose) levels will be checked every hour for three hours.
  • If two or more of these values are elevated, then your doctor will diagnose diabetes in your pregnancy.

If you are tested in the first trimester and have an abnormal three-hour glucose tolerance test, you most likely had diabetes before you became pregnant, rather than true gestational diabetes. This distinction is important in planning your pregnancy with diabetes.

Quantitative Beta-hCG Hormone Testing

If you experience vaginal bleeding or lower abdominal pain or have a history of recurrent miscarriages or ectopic pregnancies, your provider may want to test your blood for your beta-hCG hormone level (beta-hCG is produced by the placenta and is the hormone that is measured in pregnancy tests). In normal pregnancies, beta-hCG levels rise very quickly, doubling at least every 48 hours.

Abnormal levels of beta-hCG may indicate an ectopic pregnancy (a pregnancy outside of the uterus) or an impending miscarriage. If you have an abnormal level of beta-hCG hormone for your stage of pregnancy, your provider will probably order an ultrasound to determine whether the pregnancy is developing normally.

Ultrasound can identify pregnancies that are non-viable (not capable of surviving). For example, if there is a large amniotic sac and no evidence of a fetus, the pregnancy is probably non-viable. In other circumstances, the developing fetus may be seen on ultrasound, but there is no heartbeat. This is called a missed abortion.

If there is no evidence of pregnancy in the uterus and your bhCG levels are high, you may have an ectopic pregnancy. This is a serious situation and must be aggressively treated with medications or surgery.

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