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Carrier Testing for Genetic Disorders

We now know that everyone is a carrier for one or more genetic conditions.  Therefore, the American College of Obstetricians and Gynecologists (ACOG)  recommends all couples considering having children be offered carrier testing prior to or during pregnancy.  

What is Carrier Testing?

Typically the term ‘carrier' is used when describing someone who has a gene that does not work properly but does not have the condition because they also have a gene that compensates for the faulty one.  Therefore, most people who are carriers would never know they are a carrier. In the past, only when two individuals had an affected child did they find out they were both carriers of a gene mutation.  Now it is possible to test couples for one or more genetic conditions prior to becoming pregnant or during the course of pregnancy.

Who Should Consider Carrier Testing?

Since its inception, carrier testing was based primarily on ethnicity.  For example, African Americans were recommended to test for sickle cell anemia while Caucasians were offered testing for cystic fibrosis.  In the past few years, expanded carrier testing has become a hot topic.  Should all couples be tested for all conditions?  Providers wondered if couples would be able to handle all the information that may come from testing for 100 or more conditions.

Since expanded carrier testing has become more common place, we have found that only about one percent of couples will actually be at risk.  In fact, most couples end up being reassured by testing.

What Difference Does Carrier Testing Make?

One question commonly asked is, “why would we do carrier testing, we wouldn't do anything different anyway?” 

Carrier testing may not change how a couple proceeds with conception, but it could change management after delivery.  For many genetic conditions, there are treatments or therapies.  With early detection, individuals with some genetic conditions can have very healthy, fulfilling lives.  Today, all states now offer newborn screening, because if a condition is detected early enough, it could save a child's life.

However, newborn screening has limitations.  First, it only tests for about 30 to 40 conditions.  Another limitation is that the results are not always returned in time for treatment.  If a couple knew they were at risk, the child could be tested during pregnancy or right at birth to know if the child was affected.  If nothing else, treatment could start in the event that testing did come back with a positive result.  

Carrier Testing Before Conception

Carrier testing could also impact how a couple decides to proceed with conception.  Some couples with a child with a genetic condition will pursue pre-implantation genetic diagnosis (PGD) in subsequent pregnancies.  In PGD, a woman undergoes egg retrieval through a process called in vitro fertilization, and those eggs are then fertilized.  All embryos that are created are tested for the carrier condition and only those without the condition are placed back into the mother's uterus in hopes for a successful pregnancy.  

Lessons Learned

Carrier testing has been available for some time and can be very helpful for future parents. For example, one of my patients had twins who had features similar to cystic fibrosis at birth.  Because they were born premature, testing for CF was delayed.  During those few days of waiting for genetic testing results, the mother and I had a conversation about carrier testing.  Prior to delivery, she felt there was no good reason to do carrier testing.  After delivery and during the waiting period though, she expressed how she wished that we would have made them do the testing so she could have a better idea of what the twins were dealing with and how to best prepare for their needs.  This experience cemented in my mind the importance of educating future parents about the significance of being empowered with this information.

The hope of every parent is to have a healthy child.  While carrier testing can't guarantee a healthy child, it can help a couple make the best decision for their family.  Whether it is for reassurance, care of an infant, or pursuing PGD, all couples should be offered carrier testing prior to conception or during pregnancy so they can make the best decisions possible for their family. 

If you have questions about carrier testing or would like to undergo carrier testing, a genetic counselor can help.  They can walk you through the decision-making process, help you decide what testing option is best for your family and will make sense of the results when they are complete. You can connect with a genetic counselor in your area using NSGC's “ Find a Genetic Counselor ” tool. 

Jay Flanagan, MS, CGC , is a preconception and prenatal expert for the National Society of Genetic Counselors and is a genetic counselor at Sanford Health in Sioux Falls, South Dakota.