What Is Carrier Screening?
Carrier screening is a type of genetic test that can show whether you carry a gene for certain genetic disorders. When performed before or during pregnancy, it helps you understand your chance of having a child with a genetic condition.
What Is a Recessive Disorder?
Most carrier screening tests look for recessive disorders. To have a recessive condition, a person must inherit two copies of the gene—one from each parent. If someone has only one copy of the gene, they are called a carrier. Carriers often do not know they carry a gene for a disorder, as they usually have no symptoms or only mild symptoms.
What Is the Risk of Having a Child With a Recessive Disorder?
If both parents are carriers for the same disorder, there is a 25% chance their child will inherit the condition. The child has a 50% chance of being a carrier like the parents, and a 25% chance of not inheriting the gene at all. If only one parent is a carrier, the child has a 50% chance of being a carrier.
How Is Carrier Screening Done?
Carrier screening is done with a sample of blood, saliva, or a swab from inside the cheek. Test results can be negative (no gene detected) or positive (gene detected). Typically, the partner most likely to be a carrier is tested first. If that partner is not a carrier, no further testing is needed. If they are a carrier, the other partner is tested. Once you are screened for a specific disorder, you do not need to repeat the test for that condition.
When Can Carrier Screening Be Done?
Some people choose to have carrier screening before trying to conceive. It can also be done during pregnancy. Testing before pregnancy provides more options and time to make informed decisions.
Do I Have to Get Carrier Screening?
Carrier screening is your choice. You may choose to have it or not—there is no right or wrong decision.
Which Carrier Screening Tests Are Available?
Carrier screening is available for a limited number of conditions, including:
- Cystic fibrosis
- Fragile X syndrome
- Sickle cell disease
- Tay-Sachs disease
Some of these conditions are more common in certain ethnic groups. For example, sickle cell disease is more frequent among people of African descent, and Tay-Sachs is more common among Ashkenazi Jews, French-Canadian, and Cajun populations. However, anyone can carry these conditions.
Who Should Have Carrier Screening?
All women planning a pregnancy or already pregnant are routinely offered screening for cystic fibrosis, hemoglobinopathies, and spinal muscular atrophy (SMA). Additional conditions may also be screened depending on personal or family history.
What Is Targeted Carrier Screening?
Targeted carrier screening is based on ethnic background or family history. If you belong to a group with higher carrier frequency for a specific disorder, testing may be recommended. This is sometimes called ethnicity-based screening. If there is a known family history of a disorder, testing is recommended regardless of background.
What Is Expanded Carrier Screening?
Expanded carrier screening uses a single sample to test for many conditions, regardless of ethnicity or background. Companies that offer expanded screening provide their own lists of conditions, called panels. Some panels test for more than 100 disorders, usually focusing on serious conditions that affect quality of life from an early age.
Is One Approach Better Than the Other?
Before testing, you and your gynecologist can discuss the benefits and limitations of each approach. You may also meet with a genetic counselor. In some cases, both targeted and expanded screening may be combined based on your personal situation.
What If My Partner and I Are Carriers?
If both partners are carriers of the same condition and screening was done before pregnancy, options may include:
- Proceeding with pregnancy and using prenatal diagnostic testing
- Using donor sperm or eggs with IVF (in some countries; not legally available everywhere)
- Choosing not to conceive
- Considering adoption
If screening is done during pregnancy, options may be more limited, but your doctor or genetic counselor will help you understand the risks and decisions.
How Accurate Is Carrier Screening?
In rare cases, results may be incorrect. A false negative occurs if the test misses a gene that is present. A false positive occurs if the test incorrectly identifies a gene that is not there.
Are Carrier Screening Results Confidential?
In the U.S., the Genetic Information Nondiscrimination Act (GINA) of 2008 makes it illegal for most health insurers to request or use genetic test results when making coverage or rate decisions, and it prevents employers from discriminating based on genetic information. However, GINA does not apply to life, long-term care, or disability insurance.
If you discover that you are a carrier for a genetic disorder, you may choose to share this information with relatives, since they may also be at risk. However, you are not legally required to do so, and this information cannot be shared without your consent. Your doctor or genetic counselor can advise on the best way to communicate this if you choose.
