Types of Genetic Testing

Prenatal genetic testing ranges from screening tests, done with ultrasound and/or bloodwork, to diagnostic tests, which look at samples of amniotic (amniocentesis) or placental (chorionic villus sampling) tissue.1,2,3,4,5,6,7 Here are the primary types of genetic testing, their timing and what each explores:

Screening Test: Non-invasive Prenatal Testing

Non-invasive prenatal testing (NIPT), also known as cell-free DNA testing, is performed with a blood draw and is the most accurate prenatal genetic screening test.2 You can have NIPT starting in week 9 or 10 of your pregnancy, but there’s no limit to how late you can take this test.2 During pregnancy, your baby’s placenta releases DNA into your blood stream. By examining the placental DNA in your blood, this test detects the potential for various possible chromosome differences.2 These include Down syndrome, trisomy 13 and 18, and Turner Syndrome.1,2,3 While NIPT can reveal the likelihood of these chromosomal differences, a diagnostic test can provide more definitive results.1,2,3

Screening Test: Nuchal Translucency Ultrasound

Between weeks 10 and 13 of pregnancy, a nuchal translucency (NT) ultrasound can be used to take a close look at the thickness of the fluid buildup at the back of the fetus’ neck.7 If this area is thicker than normal, it could signal the potential of chromosomal differences including Down syndrome and trisomy 18 or heart issues.7

Diagnostic Test: Chorionic Villus Sampling

Chorionic villus sampling (CVS) is an optional diagnostic test that is usually done between weeks 10 and 13 of a pregnancy.6 A small sample of tissue from the placenta is collected and examined.6 This test can determine if a baby is at risk for having a genetic condition such as Down syndrome or diseases that can run in families such as Tay-Sachs disease or hemophilia.

Diagnostic Test: Amniocentesis

What is amniocentesis? It’s an optional diagnostic test that can be performed at or around week 16 of pregnancy, though it’s sometimes offered later.1,4 In this procedure, a small quantity of amniotic fluid is removed from the uterus.4,5 That fluid is then tested to show the likelihood of several chromosomal differences such as Down syndrome.4,5 Amniocentesis also reveals fetal sex and maturity.4 Amniocentesis can’t identify many common birth defects such as cleft lip, cleft palate or heart abnormalities.

A Few Caveats

While genetic testing may offer information many families would like to have, it has limitations. Here are a few caveats to keep in mind:

  • Screenings can’t detect every instance of these genetic conditions, but they do predict most of them.1
  • No screening or test can guarantee the health of a baby.
  • NIPTs aren’t recommended if you are expecting multiple (more than two) babies or if you’ve experienced co-twin demise, where one twin is lost.2
  • The earlier you begin prenatal genetic testing, the more options of tests you have.1
  • Diagnostic tests may involve the risk of miscarriage or complications.
  • Please consult your medical professional for full details of all genetic screenings and tests.

Prenatal genetic testing is an option for those who want it and have access, but it’s not medically required. For those who choose them, these tests can provide some peace of mind and insight during a process that is naturally filled with mystery. For more information about pregnancy and ways to support the development of your baby, please visit our Prenatal Hub.