Why is carrier screening recommended?

Carrier screening is one of many tests that provides information to you and your doctor about your reproductive risks prior to or during pregnancy. With each pregnancy there is a small chance of having a baby with a severe genetic disorder. Carrier screening helps determine what this chance is for you.

What is a carrier?

Everyone has two copies of each gene, one from their biological mother and another from their biological father. Being a carrier means that one copy of a gene has a change, called a mutation, which causes it to not work properly. Carriers still have one working copy of the gene, so they typically do not have any health problems associated with carrying a mutation. Therefore, many people can be carriers of a disease-causing mutation without even knowing it. Being a carrier, however, means there is an increased chance that your child could be born with a genetic disorder. Genetic disorders include conditions such as cystic fibrosis, spinal muscular atrophy, and Tay-Sachs disease.

Could I be a carrier?

Anyone can be a carrier of a genetic disorder, even if no one in your family is affected. Most people do not know they are carriers until after they are screened because carriers do not have symptoms. The chance of being a carrier is based on your ethnic background and family history; however, some disorders are fairly common regardless of these factors.

How is carrier screening done?

Carrier screening is typically done through a simple blood test. Your doctor will decide which tests are appropriate for you, draw one to two tubes of blood, and send them out for testing. It takes about two weeks to get your test results.

Is carrier screening right for me?

Carrier screening can provide you with information that might be helpful if you:

  • Are planning a pregnancy
  • Have a family history of a genetic disorder
  • Are at increased risk for specific conditions based on ethnicity, such as the following ethnic groups: Ashkenazi Jewish, French Canadian, and Cajun
  • Would like additional information about your reproductive risks

Discussing the benefits and limitations of carrier screening with a qualified health care professional, like a genetic counselor, may help you decide if carrier screening is right for you.

How do I receive my test results?

Once completed, your results will be provided to your ordering doctor who will then share them with you.

Who talks to me about my results?

Typically your doctor or a member of the medical staff will talk to you about your results. If you have any questions, you can speak with a certified genetic counselor. You can find a local genetic counselor by visiting www.NSGC.org.

What happens if I am a carrier?

For most disorders, if you are a carrier, the next step is to have your reproductive partner tested to see if he/she is also a carrier. The likelihood that your reproductive partner is a carrier of the same disorder depends on the disorder and his or her ethnic background.

Fragile X syndrome is a special situation. Fragile X syndrome is inherited on the X chromosome, and passed on from a female to her children. If a female is identified as a carrier, no further testing is necessary on her partner.

What if my partner and I are both carriers for the same genetic disorder?

If both you and your partner are carriers of the same disorder, there is a 25% chance that your child will inherit the mutation from each of you and, therefore, have the disorder.  The probability is the same regardless of your ethnic background or your family history.

For couples who have an increased risk of having a child with a specific genetic disorder, there are several reproductive options available for you and your partner:

  • Continue with family planning and pregnancy without prenatal testing
  • Prenatal testing by chorionic villus sampling (CVS) at 10-12 weeks of pregnancy or amniocentesis at 15-18 weeks of pregnancy
  • In vitro fertilization (IVF) and preimplantation genetic diagnosis (PGD) of the embryos prior to implantation and pregnancy
  • Egg or sperm donation; screening the donor for the specific high-risk disorder is recommended
  • Adoption is also available to couples who wish to have a child

Because the genetics of Fragile X syndrome and Alpha Thalassemia are complex, carriers of these disorders have different reproductive risks than those discussed here.

Speaking with your doctor or a genetic counselor will help you better understand your results, risks, and reproductive options.

Contributed by: Good Start Genetics