What is Carrier Screening?

Written by Shirah Segal, reviewed and edited by Rachel Baer, MSc, and Andrew McCarty, MS, CGC

 

What is carrier screening?

Carrier screening is a type of genetic test that can determine whether someone carries a disease-causing variant that can be passed on to their biological children. The conditions that are included in carrier screening tests are often though not always recessive, meaning that a child would only be affected if they inherit one changed copy of the gene from each parent. Individuals who have only one affected gene are called carriers. Carriers are often healthy and symptom-free, but they may pass on the variant to their biological children. Carrier screening can help reproductive partners determine their risk of having a biological child with certain inherited genetic conditions (1).

Who should get carrier screening?

Carrier screening is recommended for anyone who is planning a pregnancy or who is currently pregnant, regardless of family history or ethnicity. The purpose of carrier screening is to identify the risk of passing on certain inherited genetic conditions to biological children (2). 


When to get carrier screening?

Carrier screening is ideally performed when considering a pregnancy, in order to allow time for reproductive decision-making. However, if not performed before conception, carrier screening can still be done throughout the pregnancy. If the results show that the reproductive partners are both carriers for the same genetic condition, additional diagnostic tests may be available to determine if the embryo is affected. These tests may include procedures such as an amniocentesis and chorionic villus sampling (1).

What Types of Disorders Can Be Identified by Carrier Screening?

Recessive Conditions

In autosomal recessive conditions, a child inherits a non-functional copy of a gene from each parent. There are several ways this can happen:

  1. If both parents have the recessive genetic condition, neither of them has any functioning copies of the gene and 100% of their children will also have the recessive genetic condition.

  2. If one parent has the recessive genetic condition themselves, then both copies of the gene are non-functional. If their reproductive partner is also a carrier for this condition, that means there is a 50% chance for each child to inherit the condition:

    • No matter what, they will inherit a faulty copy of the gene from the affected parent. Then they will either inherit the functioning copy of the gene from their other parent, making them a carrier for the condition, or they can inherit a second non-functioning copy of the gene from their second parent and they will be have the genetic condition themselves.

  3. If one parent has the recessive genetic condition themselves, but the other parent does not have the condition and is not a carrier for the condition, 100% of their children would be carriers of the condition, but would not have the condition themselves.

  4. If one parent is a carrier for the recessive genetic condition and the other parent is not, there is a 50% chance for each of their children to be a carrier.

  5. If both parents are carriers for the recessive genetic condition:

    • There is a 25% chance for each child to have the recessive genetic condition

    • There is a 50% chance for each child that they will be a carrier for the genetic condition

    • There is a 25% chance for each child that they will neither be a carrier for the condition, or have the condition themselves

X-linked Conditions

X-linked carrier screening detects changes in genes on the X chromosome. Females have two X chromosomes, so if one copy of an X-linked gene carries a disease-causing variant, the other functioning copy often prevents symptoms. Males have only one X chromosome, so if they inherit a variant in an X-linked gene, they will be affected by the condition. 

For an adult male affected by an X-linked condition, the chance of passing on the condition to biological children depends on the sex of the child:

  • Male children inherit a Y chromosome rather than the affected X chromosome, so male children would not be affected by the condition.

  • All female children would inherit the affected X chromosome and would be carriers of the condition. 

If a female is a carrier of an X-linked condition, with each pregnancy, there is:

  • A 25% chance of having an affected male child

  • A 25% chance of having an unaffected male child

  • A 25% chance of having an unaffected female child

  • A 25% chance of having a carrier female child (25, 26, 27)

What are the possible Results of Carrier Screening?

Carrier screening can not detect 100% of carriers, and there are diseases with complex inheritance patterns or whose genetic cause is unknown.

There are two types of results that can be returned from carrier screening (1):

  1. Negative

    • This means that the genetic test did not detect a disease-causing variant in the individual. No test is perfect, but this means that the risk of passing down a genetic condition that was tested for is significantly reduced.

  2. Positive

    • This means that the individual carries one or more changes in their DNA, which can be passed down to their biological children

    • If the individual’s reproductive partner is not a carrier for the same variant, the risk of having a child with that condition is much lower. However, with each pregnancy, there is a 50% chance of the child being a carrier of that variant

    • If both reproductive partners are positive for the same variant in an autosomal recessive case, with each pregnancy, there is a:

      • 25% (¼) chance of the child inheriting a changed gene from each parent, and the child will be affected by the condition

      • 50% (½) chance of the child inheriting one gene with the variant and one gene without the variant. The child will not be affected by the condition, but they will be a carrier and can pass down the variant to their future children

      • 25% (¼) chance of inheriting two copies of the gene without the variant. This child will not have the condition and cannot pass down the variant to their future offspring

Options for testing in individuals identified at high risk:

There are several options available for reproductive partners who are carriers of the same disorder and wish to avoid the risk of passing it down to their biological children.

  • Partners may choose to conceive naturally, and then perform prenatal fetal testing such as an amniocentesis or chorionic villus sampling. These testing options can allow partners to determine whether the fetus is affected by the genetic condition and can lead to further reproductive decision-making.

  • Another option available for partners who are both carriers is In Vitro Fertilization (IVF) with Pre-Implantation Genetic Testing for Monogenic Disease (PGT-M). During this process, eggs are collected from the female partner and fertilized with sperm from the male partner. The embryo initially develops outside of the body, in a specialized laboratory setting (40). Once the embryo reaches the blastocyst stage, a few cells are removed and tested for the known genetic condition. This allows embryos that are not affected by the condition to be selected for transfer into the uterus (41). 

 

How Can Clover Genetics Help?

We can provide risk assessments and assist in helping individuals or couples understand their likelihood of passing on a genetic condition to their future children

  • We can facilitate carrier screenings by request in coordination with an individual’s physician or facilitated through our team.

Citations:

  1. “Carrier Screening.” Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/carrier-screening 

  2. ‌“Carrier Screening for Genetic Conditions.” American College of Obstetricians and Gynecologists. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/03/carrier-screening-for-genetic-conditions 

  3. “Cystic Fibrosis.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/9358-cystic-fibrosis 

  4. “Basics of the CFTR Protein." Cystic Fibrosis Foundation. https://www.cff.org/research-clinical-trials/basics-cftr-protein 

  5. “Tay-Sachs Disease.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/14348-tay-sachs-disease 

  6. “Tay-Sachs Disease.” Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/tay-sachs-disease/symptoms-causes/syc-20378190 

  7. “Sickle Cell Disease.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/12100-sickle-cell-disease 

  8. “Sickle Cell Disease.” National Heart, Lung, and Blood Institute. https://www.nhlbi.nih.gov/health/sickle-cell-disease/causes 

  9. “Thalassemia.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/14508-thalassemias 

  10. “Alpha Thalassemia.” Medline Plus. https://medlineplus.gov/genetics/condition/alpha-thalassemia/#causes 

  11. “Beta Thalassemia.” Medline Plus. https://medlineplus.gov/genetics/condition/beta-thalassemia/#causes 

  12. “Thalassemia.” Medline Plus. https://medlineplus.gov/thalassemia.html 

  13. “About Thalassemia.” CDC. https://www.cdc.gov/thalassemia/about/ 

  14. “Congenital Adrenal Hyperplasia.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/17817-congenital-adrenal-hyperplasia  

  15. Krone N, Arlt W. Genetics of congenital adrenal hyperplasia. Best Pract Res Clin Endocrinol Metab. 2009;23(2):181-192. doi:10.1016/j.beem.2008.10.014 ; https://pmc.ncbi.nlm.nih.gov/articles/PMC5576025/ 

  16. “Spinal Muscular Atrophy.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/14505-spinal-muscular-atrophy-sma 

  17. “Spinal Muscular Atrophy.” Medline Plus. https://medlineplus.gov/spinalmuscularatrophy.html 

  18. “Canavan Disease.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/6013-canavan-disease 

  19. “Canavan Disease.” Medline Plus. https://medlineplus.gov/genetics/condition/canavan-disease/ 

  20. “Familial Dysautonomia.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/24220-familial-dysautonomia 

  21. “ELP1 Gene.” Medline Plus. https://medlineplus.gov/genetics/gene/elp1/ 

  22. “Gaucher Disease.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/16234-gaucher-disease 

  23. “Gaucher Disease.” Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/gauchers-disease/symptoms-causes/syc-20355546 

  24. “What is Gaucher Disease?” National Gaucher Foundation. https://www.gaucherdisease.org/about-gaucher-disease/what-is/ 

  25. “Horizon Advanced Carrier Screening.” Natera. https://www.natera.com/womens-health/horizon-advanced-carrier-screening/patients/ 

  26. “Carrier Screening.” Washington State Department of Health. https://doh.wa.gov/you-and-your-family/genetic-services/health-care-providers/carrier-screening 

  27. Bin Shlhoob R, Tanaka J, Pandya AM. Genetics, X-Linked Inheritance. (Updated 2026 Mar 22]. In: StatPearls (Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557383/   

  28. “About Fragile X Syndrome.” CDC. https://www.cdc.gov/fragile-x-syndrome/about/ 

  29. “Fragile X Syndrome.” Medline Plus. https://medlineplus.gov/fragilexsyndrome.html 

  30. “Fragile X Syndrome.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/5476-fragile-x-syndrome 

  31. “How Fragile X Syndrome Is Inherited.” CDC. https://www.cdc.gov/fragile-x-syndrome/about/how-fragile-x-syndrome-is-inherited.html 

  32. “About Duchenne Muscular Dystrophy.” National Human Genome Research Institution. https://www.genome.gov/Genetic-Disorders/Duchenne-Muscular-Dystrophy 

  33. “Duchenne Muscular Dystrophy.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/23538-duchenne-muscular-dystrophy-dmd 

  34. “Duchenne Muscular Dystrophy.” Muscular Dystrophy Association. https://www.mda.org/disease/duchenne-muscular-dystrophy#what-is-dmd 

  35. “Hemophilia.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/14083-hemophilia 

  36. “Hemophilia.” Medline Plus. https://medlineplus.gov/hemophilia.html 

  37. “Hemophilia.” Medline Plus. https://medlineplus.gov/genetics/condition/hemophilia/#causes 

  38. “Fabry Disease.” Medline Plus. https://medlineplus.gov/genetics/condition/fabry-disease/#causes 

  39. “Fabry Disease.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/16235-fabry-disease 

  40. “In Vitro Fertilization.” Medline Plus. https://medlineplus.gov/ency/article/007279.htm 

  41. “Preimplantation Genetic Testing.” Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/preimplantation-genetic-testing-pgt