Prenatal Genetic Testing
What is Prenatal Genetic Testing?
More than 95% of all newborns are born without birth defects, however, approximately 3-5% of infants will be born with some type of birth defect, and many of these birth defects are caused by genetic disorders. Examples of genetic disorders are trisomy 21 (Down’s Syndrome), cystic fibrosis, and sickle cell disease. Prenatal genetic testing refers to tests offered during pregnancy to look for these and other genetic disorders.
There are two types of genetic tests.
1) Screening tests help expectant parents understand if they are at low risk or high risk for having an infant with a genetic disorder. They do not give a yes or no answer – they provide an estimate of whether a disorder may be present. These tests create no risk to the pregnancy. Common screening tests include the Nuchal Translucency test for Down’s Syndrome and the Cystic Fibrosis carrier test.
2) Diagnostic tests are used to confirm whether or not a condition is present in an infant. Chorionic villus sampling and amniocentesis are diagnostic tests. Diagnostic tests do involve a risk of miscarriage.
Will I have prenatal genetic testing?
Testing for cystic fibrosis and trisomy (13, 18, 21) are offered to all of our patients in their first trimester. In addition, all patients are offered the AFP test at 16 weeks to help determine their risks for having a baby with spina bifida. Certain ethnic groups are at risk for other genetic disorders, and those patients will be offered additional testing. Your provider will talk with you about genetic testing at your first visit and will help you decide which tests are appropriate for you. Genetic testing is optional and there are several questions to consider when you are deciding if you want genetic testing.
- Do I want the information provided by genetic testing?
- Do I want to know about these birth defects before my baby is born?
- Will having this information help me make choices about my pregnancy?
- Will doing these tests make me feel less anxious about my pregnancy?
There is no right or wrong choice about genetic testing. Your provider will talk with you more about genetic testing at your first visit and try to help you with your choice. If you have additional questions or have had a previous pregnancy affected by a genetic disorder we may arrange for you to see a genetics counselor.
Which genetic tests are available to me?
The following are the genetic tests we offer. Links to the tests will provide more specific information about each test. These are all screening tests.
Autosomal recessive disease screening
Blood tests offered to patients based on ethnicity or other factors that may increase their risk for having a child with an autosomal recessive disorder.
First Trimester Screening with Nuchal Translucency
Offered between 11 and 14 weeks and includes an ultrasound and a blood test. Used to predict the risk of having a baby with trisomy 13, 18 and 21.
Cystic Fibrosis Carrier Screening
A blood test offered at your first visit to see if you are a carrier of the cystic fibrosis gene.
A blood test ordered at 16 weeks to test for trisomy 13, 18 and 21. This test if for patients for whom the Nuchal Translucency test could not be completed.
Non-Invasive Prenatal Testing (NIPT)
A blood test ordered at 10-12 weeks to test high-risk patients for trisomy 13, 18, and 21. Only those patient at increased risk for trisomy are eligible for this test.
Offered to all patients at 16 weeks to predict the risk of having an infant with a spinal cord defect.
All patients are scheduled for a screening ultrasound between 20-22 weeks to look for a variety of birth defects.
Diagnostic tests are available through referral to a Maternal Fetal Medicine specialist. Diagnostic tests may be recommended if you have had a previous pregnancy with a genetic disorder or if you are at higher risk for a genetic disorder due to your own medical or family history. Diagnostic tests are also offered to patients that have an abnormal screening test.
Are other genetic tests available?
Advances in genetic testing means that new tests are frequently marketed to expectant parents. The tests that are available change frequently and may or may not provide useful information regarding risks for your own pregnancy. These tests are not routinely offered to our patients. You should speak with your provider if you have questions about other genetic tests that are available.
For additional information:
Frequently asked questions about screening tests for birth defects:
Video – Chromosome Abnormalities: Prenatal Screening and Diagnosis
Video – Genetic Disease Carrier Screening