What is Carrier Screening and Why is it Important for Fertility?

researcher in lab

What is carrier screening?

Carrier screening is a type of genetic test. It looks specifically for genetic variations that can negatively affect one’s children. Adults may “carry” these genetic variations (often simply called “variants”) without showing any signs or symptoms of the condition themselves, while still being at risk of passing it on to future offspring. Progyny partner Fulgent Genetics broke down the ins and outs of carrier screening, to give you an important picture.

Is it possible for me to be a carrier for a condition that doesn’t run in my family?

Yes – the idea behind the conditions that carrier screening tests for is that they often won’t show up in a family until two genetic contributors (or biological parents) are carriers for the same condition.

Who is carrier screening recommended for?

Carrier screening is recommended for anyone who is currently pregnant or planning to become pregnant in the future, according to current guidelines put forth by organizations such as the American College of Medical Genetics and Genomics, the American College of Obstetricians and Gynecologists, and the American Society for Reproductive Medicine. Usually, both genetic parents need to be carriers for the same condition for their children to be at risk of inheriting it, which is why both partners (or egg/sperm donors) may opt for carrier screening.

What are the advantages of expanded carrier screening over ethnic-based screening?

You may be offered something called “expanded” or “pan-ethnic” carrier screening, which looks for more conditions than other “ethnic-specific” carrier screening tests. These terms can mean slightly different things to different testing labs, but the idea behind expanded screening is that it covers both common and less common risks for people of all ethnic backgrounds.

In the early days of carrier screening, tests were reserved for people of specific ethnicities who were more likely to be carriers of certain conditions. But genetic conditions are not necessarily limited to one ethnic group, and many patients have mixed (or even unknown) ethnicities. Because of this, and because science now allows for more universal testing, it’s often recommended that patients opt for an expanded carrier screening test.

What kinds of conditions does carrier screening test for?

Conditions included in carrier screening tests are generally early-onset conditions that could result in severe health issues. Common carrier conditions include cystic fibrosis, fragile X syndrome, spinal muscular atrophy, and sickle cell disease, although there are hundreds of possible conditions ranging from relatively common to very rare. If you’re offered carrier screening by your care team or are looking into it yourself, you may be able to obtain a full list of conditions tested for by the laboratory performing your test.

If I test positive, what are my chances of having a child affected with a genetic condition?

Usually, your chances are still low unless your partner or egg/sperm donor is also a carrier for the same condition. Most carrier conditions are autosomal – meaning they occur within one of the 22 pairs of chromosomes that are not sex chromosomes. In these cases, when both genetic parents are carriers for the same condition, each child has a 25% chance of being affected with the condition. If only one genetic parent carries the condition, the risk of having an affected child is not zero but is extremely low.

Less common cases can include positive carrier results for an X-linked condition (related to a gene on the X chromosome). Risks for these cases can vary, but each individual report should explain what condition(s) you carry and should also explain your specific risks. Your care team or a genetic counselor can also help with interpreting results should you have any questions.

If I test negative, can my child still be affected?

A negative result means that your risk of being a carrier for the conditions included in your test is very, very low. However, it’s important to note that no test is perfect or able to guarantee the birth of a healthy baby, due to limitations in technology as well as our current understanding of genetics. If your carrier screening test is negative, though, that’s a great indicator that you likely don’t carry a variant that could affect your child (particularly for the genes included on your test).

What actions can I take based on my results?

Knowing your carrier status can allow you to make more informed family planning decisions. Individuals choosing an egg or sperm donor can use the information in their selection to help maximize the chance of a healthy baby. Reproductive couples who are carriers for the same condition can consider options such as IVF paired with preimplantation genetic testing, adoption, or using an egg or sperm donor. Alternatively, some parents may simply wish to prepare for the potential birth of a child affected by a genetic condition. All family planning options should be discussed with your healthcare provider.