Prenatal Tests
Many women who become pregnant for the first time are unaware of the numerous tests that are recommended and offered in pregnancy. Often the first visit with their provider may be a first time meeting. During this visit, part of the goal is to assess maternal health and well-being in order to assess fetal health and well-being. Some tests are done routinely on all women to assess blood type and for infections and to check for anemia. There are additional tests that are offered as optional to assess for fetal conditions such as chromosome abnormalities, structural abnormalities or other genetic conditions. It is important to note that there is no way to test for all congenital structural or genetic conditions with prenatal testing. The goal is to minimize risk, yet offer women the most accurate testing available to detect fetal conditions.
Prenatal testing includes both screening tests and diagnostic tests. Screening tests can identify whether your baby is more likely to have a certain condition, but don’t actually make a definitive diagnosis. Screening tests pose no risk to the pregnancy (considered non-invasive). Diagnostic tests are performed if the screening test reveals an increased risk for a certain condition or if the mother is at an increased risk due to age or other factors. Diagnostic tests are more invasive and they may pose an increased risk to the pregnancy.
Routine Tests
Generally at the first visit, your health care provider will order blood tests to determine/screen for:
- Blood type (A,B, AB or O)
- Rh factor (Rh positive or Rh negative)
- Anemia
- Rubella immunity status
- Hepatitis
- Human Immunodeficiency Virus
- Sexually transmitted diseases
- Thyroid function
Special Tests
(offered to certain “at risk” populations)
- Cystic Fibrosis
- Sickle Cell Disease
- Thalassemia
- Tay-Sachs
- Canavan
At each prenatal visit, your health care provider will check your urine for protein, sugar and for evidence of bacteria. In addition, your blood pressure and your weight will be checked. Your provider will also listen to your baby’s heartbeat and will measure your abdomen to follow your baby’s growth. A normal heartbeat and growth rate are important signs that your baby’s development is on track. In the beginning of the third trimester, you will be tested for diabetes and for anemia again. Finally, in the last 4-5 weeks you will be tested for colonization with Group B Streptococcus (GBS). If you test positive for the presence of GBS, antibiotics will be recommended during labor to prevent infection of the baby at the time of birth.Ultrasound:
Ultrasound
Ultrasound is generally offered to further assess fetal well-being. It is offered by most providers as routine in the second trimester when all fetal organs are developed. Ultrasound uses sound waves to show a picture of the baby on a screen. The ultrasound is not painful and is non-invasive.
Ultrasound can detect:
- Many birth defects early in pregnancy that otherwise could go undetected until birth
- Number of babies present
- Baby’s growth/confirmation of due date
- Placental position
Ultrasound is a screening test. It may miss certain conditions and it may detect findings that have no bearing on the pregnancy. Additional prenatal tests are offered to further evaluate for risks, these tests are considered optional and are generally screening tests that would require follow-up with a diagnostic test such as an amniocentesis. These optional tests are generally offered to improve the detection of a problem, but still require confirmation with a diagnostic test.
Optional Tests
- Nuchal Translucency (NT) screening – is a high-resolution ultrasound examination of the baby’s neck area (a fold of skin at the back of the neck) measured between 11-13 weeks gestation. The results can be combined with the mother’s age, and measure of specific blood proteins to determine the risk for Down syndrome or certain other chromosome abnormalities (integrated or sequential screening).
- Quad screen – is a blood test done between 15 and 20 weeks to test maternal blood levels of certain proteins to determine the risk of Down syndrome, other chromosome problems, neural-tube defects or other rare congenital defects.
If these screening tests are abnormal, an amniocentesis is recommended for definitive diagnosis. An Amniocentesis is a procedure in which a small amount of amniotic fluid is obtained and then analyzed for chromosomes and alpha fetal protein (which is usually elevated if the baby has spina bifida). The amniocentesis may risk pregnancy loss up to 0.5 percent. It is important to remember that the amniocentesis detects chromosome problems, however many genetic conditions are not tested or detected by amniocentesis unless a patient has a specific known genetic condition.