Prenatal tests are medical tests you get during pregnancy. They help your health care provider find out how you and your baby are doing. 

First-trimester Prenatal Screening Tests

First-trimester screening is a combination of fetal ultrasound and maternal blood testing. This screening process can help to determine the risk of the fetus having certain birth defects. Screening tests may be used alone or with other tests.

  • Cell-free fetal DNA testing (also called noninvasive prenatal screening or testing). Tests your blood for your baby’s DNA to see if he may have certain genetic conditions, like Down syndrome. This test is done after 10 weeks of pregnancy. Your provider may recommend the test if an ultrasound shows that your baby may have a birth defect or if you’ve already had a baby with a birth defect. It’s not recommended for women who aren’t likely to have a baby with a birth defect or who are pregnant with multiples (more than one baby, like twins or triplets). It’s called noninvasive because it’s done with a blood test. It doesn’t require any other tools that break the skin or enter your body. If you have this test, your provider may recommend you have an invasive test, like amniocentesis, to confirm the results.
  • Chorionic villus sampling (also called CVS). A test that checks tissue from the placenta to see if a baby has a genetic condition, like Down syndrome. CVS is done at 10 to 13 weeks of pregnancy. Your provider may want you to have CVS if you’re older than 35, if genetic conditions run in your family, or if your first-trimester screening shows that your baby is at increased risk for birth defects.
  • Cystic fibrosis (also called CF) carrier screening. Tests to see if you have the gene that causes CF. CF is a disease that affects breathing and digestion. If you and your partner have the gene, you can pass CF to your baby. You and your partner can have this test any time during pregnancy.
  • Early ultrasound (also called first-trimester ultrasound). Confirms (makes sure) that you’re pregnant. It also dates your pregnancy, so you know how many weeks pregnant you are. An ultrasound uses sound waves and a computer screen to show a picture of your baby inside the womb.
  • First-trimester screening. Tests to see if your baby may be at risk for some birth defects, like Down syndrome and heart defects. You get a blood test and an ultrasound as part of this test. The test usually is done at 11 to 14 weeks of pregnancy.

 If the results of these first-trimester screening tests are abnormal, genetic counseling is recommended. More testing such as chorionic villus sampling, amniocentesis, cell-free fetal DNA, or other ultrasounds may be needed for accurate diagnosis.

Second-trimester Prenatal Screening Tests

Second-trimester prenatal screening may include several blood tests, called multiple markers.  These markers give information about a woman’s risk of having a baby with certain genetic conditions or birth defects. Screening is usually done by taking a sample of the mother’s blood between the 15th and 20th weeks of pregnancy (16th to 18th is ideal). The multiple markers include:

  • Alpha-fetoprotein screening (AFP): This blood test measures the level of alpha-fetoprotein in the mothers’ blood during pregnancy. AFP is a protein normally produced by the fetal liver and is present in the fluid surrounding the fetus (amniotic fluid), and crosses the placenta into the mother’s blood. The AFP blood test is also called MSAFP (maternal serum AFP). Abnormal levels of AFP may signal:
  • Open neural tube defects (ONTD), such as spina bifida
  • Down syndrome
  • Other chromosomal abnormalities
  • Defects in the abdominal wall of the fetus
  • Twins–more than one fetus is making the protein
  • A miscalculated due date, as the levels vary throughout pregnancy

Abnormal test results of AFP and other markers may mean more testing is needed. Usually, an ultrasound is done to confirm the dates of the pregnancy and to look at the fetal spine and other body parts for defects. An amniocentesis may be needed for accurate diagnosis.

  • Maternal blood screening (also called quad screen). Tests your blood to see if your baby is at risk for some birth defects, like Down syndrome. It’s called a quad screen because it measures four substances in the mother’s blood: alpha-fetoprotein (AFP), estriol, human chorionic gonadostropin (hCG) and inhibin A. The test is done at 15 to 22 weeks of pregnancy.
  • Amniocentesis (also called amnio). Tests the amniotic fluid from around your baby to see if he has a genetic condition, like Down syndrome. The test usually is done at 15 to 20 weeks of pregnancy. Your provider may want you to have an amnio for the same reasons as for CVS.
  • Ultrasound. Helps your provider make sure your baby is growing and check for birth defects. It’s usually done at 16 to 20 weeks of pregnancy.
  • Glucose screening. Tests to see if you have gestational diabetes. This is a kind of diabetes that some women get during pregnancy. You get this test at 24 to 28 weeks of pregnancy.

Tests During The Third-Trimester 

In your last trimester, your provider does a test for group B strep (also called GBS). Group B strep is an infection you can pass to your baby during birth. The test checks fluid from your cervix to see if you have GBS. You get this test at 35 to 37 weeks of pregnancy.

Finally…

You can have several tests in your first trimester. Talk to your provider to find out which tests are right for you. Additionally, be sure to tell your provider if you notice any change in how often your baby moves. We are here for you. Contact us if you have any questions or to set up an appointment.

(Some information provided by the University of Rochester Medical Center and March of Dimes).