Prenatal Testing

During pregnancy, most women have certain routine lab tests completed.  These tests can help your provider detect possible problems with your health and your baby’s health.  You also may have additional tests ordered, depending on your medical history, family or ethnic background, or previous test results.  This page will tell you more about

• tests that are done on most pregnant women
• why and when these tests are done
• other tests that may be offered or needed

Lab tests ordered at your first nurse visit:

After the nurse completes your medical and pregnancy history forms, this information is reviewed and a provider will order your lab testing. This testing includes:

1. Blood Typing – This test determines your blood type, Rh type, and antibody factor. If your blood type is Rh negative, special monitoring of your blood may be necessary to check for Rh incompatibility.
2. Antibody Screen – detects unusual antibodies that may have arisen in a prior pregnancy or from a blood transfusion.
3. CBC (Complete Blood Count) – This test checks levels of different types of cells in your blood such as white blood cells, red blood cells and platelets.  Anemia (or low iron count) may occur in pregnancy and this test may help to determine if you are anemic.  Platelets are necessary for coagulation (or clotting).  An increase in white blood cells may indicate infection.
4. Rubella Test (German Measles) – an antibody test to determine if you are protected from Rubella.
5. Syphilis Screening (RPR/VDRL) – tests for exposure to syphilis. If present, treatment can be initiated so that the fetus is not harmed.
6. Hepatitis B (HBSAG) – checks for infection with the Hepatitis B virus, which can be passed to an unborn child.
7. HIV – checks for the HIV virus. If you have HIV infection, you can be treated during pregnancy, which will reduce the chances of you passing the virus to your unborn child. This test is included in your routine lab testing unless you indicate that you do not wish to be tested.
8. Thyroid Stimulating Hormone (TSH) – a test to determine thyroid function.
9. Urinalysis - A urine screen is used to assess bladder or kidney infections, diabetes, dehydration and preeclampsia by screening for high levels of sugars, proteins, ketones and bacteria. Repeated findings of sugar in the urine may require further testing for diabetes.. Higher levels of protein may suggest a possible urinary tract infection, or kidney disease. This test is processed through a laboratory.  A urine dipstick for protein and glucose will be completed in our office at each of your prenatal appointments.

Other initial lab tests may be ordered based on your medical history, such as:

1. Glucose levels– The level of sugar in your blood is measured to test for diabetes. For this test, you may be required to drink a special sugar mixture and then wait a period of time (determined by your provider) before your blood is tested in the lab. This test may be ordered early or later in your pregnancy. If you have risk factors for diabetes, it is done earlier.
2. Hepatitis C – Hepatitis C is a viral infection of the liver. A simple blood test can be completed if your history reveals you may be at risk.
3. Cystic Fibrosis Carrier Screening – A screening test (genetic) to determine if you may be a carrier of the Cystic Fibrosis gene mutation.  You will receive further information regarding this test during your appointment.
4. Based on your history, other genetic or diagnostic tests may be ordered.  Please ask your provider if you have questions about tests that have been ordered for you.

Testing at your first visit with your healthcare provider

On your first visit with the provider, a Pap test will be completed to check for abnormal cells of the cervix and the HPV virus.  At the same time, a sample of cervical cells will be taken to check for certain sexually transmitted infections, such as gonorrhea and Chlamydia. If an STI is present, you will be treated with antibiotics. 

Lab test results from your nurse visit will be reviewed with you.  Your provider will also discuss your options for testing for possible birth defects.

Testing for possible Birth Defects

A variety of tests are available based on the stage, or trimester, of your pregnancy.  Your provider will explain the risks and benefits of these screening tests to help you make the best choice.  If there is a history of birth defects in your family, your provider may recommend you visit a genetic counselor for more detailed information about your risks.

First Trimester Screening

First trimester screening includes a blood test and an ultrasound.  This test is usually down between 11 and 14 weeks of pregnancy and is used to detect risk for Down syndrome and trisomy 18.  The blood screens measures the levels of two substances in the mother’s blood:

• Pregnancy–associated plasma protein–A (PAPP–A)
• Human chorionic gonadotropin (hCG)

An ultrasound exam, called nuchal translucency screening, is used to measure the skin thickness at the back of the neck of the fetus. An increase in this space may be a sign of Down syndrome, trisomy 18, or other problems.

The results of the nuchal translucency screening are then combined with those of the blood tests and the mother's age to assess the risk for the fetus. In the first trimester this combined test detects Down syndrome in about 85% of cases. When the nuchal translucency thickness is increased, the fetus may have a heart defect or other genetic condition. In this case, your doctor may suggest a more detailed ultrasound exam at around 20 weeks of pregnancy.

Second Trimester Screening

In the second trimester, a test called “multiple marker screening” is offered to screen for Down syndrome, trisomy 18, and neural tube defects, such as spina bifida. This test measures the level of three or four of the following substances in your blood:

1. Alpha–fetoprotein (AFP)—A substance made by a growing fetus, which is found in amniotic fluid, fetal blood, and, in smaller amounts, in the mother's blood.
2. Estriol—A hormone made by the placenta and the liver of the fetus.
3. hCG
4. Inhibin–A–A hormone produced by the placenta.

The test using the first three of these substances is called a triple screen. When the fourth substance (inhibin–A) is added, the test is called a quadruple or “quad” screen. These tests usually are done around 15–20 weeks of pregnancy. The stage of pregnancy at the time of the test is important because levels of the substances measured change during pregnancy. The triple screen test detects Down syndrome in 70% of the cases. The quad screen detects Down syndrome in 80% of the cases. The AFP test detects neural tube defects in 80% of the cases.

Ultrasounds

An ultrasound exam is a test that makes an image of your fetus from sound waves. These sound waves are produced by a device called a transducer. The transducer is either moved across your abdomen or placed in your vagina, depending on the structures that need to be viewed.
An ultrasound exam may be done to find out the age of the fetus. It also can be used to check how the baby is growing. In some cases, it helps to confirm a diagnosis or check a possible problem. Ultrasounds are ordered by your provider based on your stage of pregnancy and your medical condition.  Many insurance plans will only cover one ultrasound during your pregnancy unless medically necessary.

Tests order later in pregnancy

At approximately 28 weeks, your provider will test your glucose level and check for anemia (or low iron) (a CBC or Hemoglobin and Hematocrit level). 

At approximately 36 weeks, you will be tested for group B streptococcus (GBS). For this test, a swab is used to take cell samples from your vagina and anal area. GBS can be passed to a baby during birth and cause problems in the first weeks of a baby's life.

If your test is positive for GBS, antibiotics can be given during labor to help prevent the baby from being infected.

In conclusion

Some tests are given to all pregnant women to help find problems that could pose a risk to the mother or the baby. Other tests are given based on risk factors, family or ethnic background, or other test results. Finding problems early allows your healthcare provider to treat them or to plan for any special care you or your baby may need.

 

Back to Top