Preconception

Genetic Carrier Screening: A Comprehensive Guide

Options, Timing, and Why It Matters

Carrier screening is genetic testing that can tell you if you carry the genes for certain genetic disorders, and can be done before or during pregnancy. A family health history of genetic disorders, birth defects, developmental disabilities, or newborn screening disorders, puts your baby at higher risk for having the same disorder(s). Understanding your family health history (and your partner’s) can help you consider all your options. Depending on your family health history or your ethnicity, your provider may refer you for genetic counseling and you may decide to have genetic carrier testing.This guide will cover what genetic carrier screening is, why it’s important, available options, timing of the testing, understanding results, and implications of test results.

What Is Genetic Carrier Screening?

Genetic carrier screening mostly tests for recessive disorders. Imagine your baby inherits two copies of each gene, one from you and one from your partner. Now, if one of you is a carrier of a gene for a condition, it means you’ve got one normal copy and one defective copy of that gene. Now, here’s where things get interesting. If both you and your partner are carriers of the same recessive disorder gene, there’s a 25% chance your baby could inherit both defective copies and end up with the disorder. However, there’s a 50% chance they’ll simply be a carrier like you, which usually means no symptoms or just very mild ones.Carrier screening is about checking for genes linked to particular inherited disorders. Some of these disorders are more prevalent in certain ethnic groups. For example, Tay-Sachs disease is more common among Ashkenazi or Eastern European Jewish populations, while sickle cell disease is more prevalent among Black communities. The screening can also detect other recessive disorders like fragile X syndrome, thalassemia, cystic fibrosis, and spinal muscular atrophy.    

What Should You Expect During Genetic Carrier Screening?

Carrier screening involves testing a sample of blood, saliva, or a cheek swab (buccal swab). This sample is sent to a lab where technicians analyze it for specific changes in DNA, chromosomes, or proteins indicating certain disorders. Results are either negative, meaning the person doesn’t carry the gene for the disorder, or positive, indicating they do. This testing can be done before or during pregnancy. Screening before pregnancy provides more options for managing positive results.

Why Is Genetic Carrier Screening Important?

Knowing you and your partner’s carrier status empowers you to make informed decisions about pregnancy, adoption, and assisted reproductive technologies. Screening before conception allows you to identify any potential risks early and plan accordingly, whether you choose to proceed with pregnancy, explore options like IVF with autologous or donor eggs or sperm, or opt for adoption. Genetic counseling, both before and after testing, is an invaluable resource to help you navigate genetic results—which can be challenging and emotionally taxing. Genetic counselors are available to offer support, guidance, and understanding of results and what they mean for you and your family. Whether you’re feeling anxious, confused, or just need someone to talk to, genetic counselors offer a compassionate ear and can connect you with additional resources and support groups to help you through the process.

What Are the Pros and Cons of Different Screening Options and Techniques?

Traditional genetic carrier screening targets testing for a single gene, usually based on factors like your ethnicity, family history, or if you’re known to be a carrier. Expanded carrier screening, on the other hand, is more comprehensive. It checks for multiple genetic disorders, regardless of your background or family history.In expanded carrier screening, testing companies create their own lists of disorders to screen for, often including over 100 different disorders, with a focus on severe ones. The big advantage here is that you can learn about a wide range of genetic disorders, even if you have no family history of them or aren’t from an affected ethnic group. The downside? You might find out you’re a carrier for disorders you never knew about. In rare cases, you might even discover you’re a carrier for something that could affect your future health.Expanded carrier screening employs advanced techniques like next generation sequencing (NGS) and microarray analysis. These methods have become more accurate and sensitive in recent years, allowing for rapid sequencing of hundreds or thousands of genes or even whole genomes.

When is the Optimal Timing for Genetic Carrier Screening?

Preconception screening offers clear benefits as it allows individuals to know their carrier status before trying to conceive. If one or both partners are carriers, they can understand the risks and make informed decisions about their options. Consider carrier screening if either partner has a family history of a disorder, comes from an ethnic group with known risks, or has a history of miscarriage or birth defects in previous pregnancies.When considering prenatal genetic screening, think about how you would use the results in your pregnancy care. Some parents want to be prepared for the possibility of their baby being born with a genetic disorder, so they can plan for necessary medical care. Others may decide to terminate the pregnancy under certain circumstances. Your personal beliefs and values should guide your decision to test or not.If you undergo carrier screening during the first trimester of pregnancy and one of you is found to be a carrier, your provider may suggest chorionic villus sampling (CVS) to test your fetus. If you haven’t had carrier screening before, your provider may recommend CVS. Factors leading to recommendation for CVS include history of genetic disorders, if you’re over 35, or if first-trimester screening shows an increased risk of birth defects. CVS, typically performed at 10 to 13 weeks, tests a small piece of placental tissue for genetic conditions.Usually, carrier screening doesn’t need to be repeated. However, if there are new risks or changes in family history, your provider may suggest retesting, though this is uncommon.

Understanding Results and Implications

Genetic counselors and your OB/GYN or another healthcare provider will help interpret the genetic test results. A positive result indicates being a carrier for a genetic disorder, while a negative result means not being a carrier for a specific gene variant. Sometimes, results don’t provide useful information, termed uninformative, inconclusive, ambiguous, or indeterminate. Such results can’t confirm or deny a specific diagnosis, but testing other family members may help interpret them.If preconception screening shows carrier status for a genetic disorder, genetic counseling assists in understanding the implications. It helps assess the risk of the fetus having or being a carrier of the disorder and discusses implications for offspring. If prenatal screening reveals a genetic disorder, options are discussed.Throughout, genetic counselors offer emotional support, coping strategies, and decision-making guidance. They help in making informed decisions about family planning, reproductive options, and necessary interventions. Results need to be communicated to relevant healthcare providers, partners, and family members, with the genetic counselor providing support and coping strategies.

Making Informed Decisions for Your Family’s Future

If you have a family history of genetic disorders or belong to an ethnic group which is at higher risk of certain disorders, genetic carrier screening can be an invaluable component of family planning and your reproductive health. Preconception screening especially empowers you to make decisions proactively before getting pregnant. People who are planning to get pregnant or are expecting can seek information as early as possible, ask questions, and collaborate with their health care providers to make informed choices.

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