What Is Carrier Screening?

A couple talking to a genetic counselor

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Carrier screening is a type of genetic testing that checks if a person who is pregnant (or intending to get pregnant) carries genes for specific genetic disorders. This testing allows people to assess their risk of passing on certain genetic conditions to their children.

Carrier screening is a tool that people who are pregnant and hoping to get pregnant can use to assess some of the potential health challenges their future baby may face. Your OB/GYN and/or genetic counselor can help you determine which genetic conditions to screen for and will assist you in interpreting your results. Learn more about carrier screening, which genetic conditions are tested for, what the results mean, and what your options are if you test positive.

What Is Carrier Screening?

There are numerous possible screenings that can be done before and during pregnancy. Carrier screening is one of these options that's often recommended during prenatal care. You and your healthcare provider can decide whether carrier screening makes sense for you, and if so, which genetic disorders to test for.

"Carrier screening is a genetic test that can be done through blood work or a saliva sample to help identify individuals who may have a higher chance of having a child with certain genetic disorders such as cystic fibrosis, sickle cell disease, or spinal muscular atrophy," says Trisha Shires, a certified genetic counselor in the department of obstetrics and gynecology in the center for Advanced Maternal and Fetal Care and High-Risk Pregnancy at the University of Kansas Health System.

Being a carrier means that you have a gene in your DNA for that condition. It does not mean your baby will get the condition or that you have the disorder. Instead, this testing is an informational tool that can help you make decisions about getting pregnant and/or your pregnancy. Additionally, your results can impact the care you and your future baby receive during pregnancy and the postpartum period.

When Is Carrier Screening Done?

Carrier screening can be done before or during pregnancy. "I always advocate that the best time to do carrier screening is before getting pregnant, but the testing often occurs after conception as people don't usually know about it beforehand," says Cori Feist, a licensed certified genetic counselor at Oregon Health Sciences University in Portland, Oregon.

Knowing your carrier screening results ahead of pregnancy allows time to weigh all the information and offers the choice to pursue other ways of having a baby (such as in vitro fertilization (IVF) and adoption) that will reduce the risk of passing on a genetic disorder, explains Hannah Elfman, MS, CGC, a genetic counselor at Children’s Hospital Colorado and University of Colorado Hospital.

Plus, testing allows for more informed care during pregnancy and after the baby is born. However, the testing can—and often is—also done during pregnancy.

Knowing that you have increased odds of having a baby with a certain genetic disorder gives you the option to screen the growing fetus for the disorder in utero. This can often be done with chorionic villus sampling (CVS) or amniocentesis. These tests can be performed late in the first trimester or early in the second trimester, respectively.

What Does Carrier Screening Test For?

There are many options available for carrier screening. They range from testing for one or two specific genetic disorders to having an expanded carrier screening panel done that includes evaluation for several hundred genetic disorders, explains Shire. It's really up to you and your provider to decide how much information you want or need and what to test for.

"Each person who gets carrier screening will have a higher or lower risk of having genes for different genetic disorders," says Elfman. People also have different comfort levels or beliefs around whether or not they want to know this information and what they will do with their results. They will be screened for the specific panel of genetic conditions that makes the most sense for them. Other people decide not to do carrier screening at all.

"The type of testing done can depend on the level of information that an individual wants as well as the individual’s family and medical history," says Shire.

Other factors that influence which disorders you are screened for are the recommendations and preferences of your healthcare provider, the health facility you are working with, and your insurance coverage. "A lot of insurance companies will cover carrier screening once you’re pregnant but may not preconceptionally," notes Feist. It's important to check with your insurance company to determine what will be covered and how much your out-of-pocket cost will be.

While everyone is screened for a different set of disorders, the most common are cystic fibrosis, fragile X syndrome, and muscular dystrophy, says Fiest. These (and the other genetic disorders that are screened for) fall into two main categories: autosomal recessive inheritance and X-linked inheritance.

Autosomal Recessive Inheritance

The vast majority of genetic disorders on carrier screening panels follow autosomal recessive inheritance. "With this type of inheritance, both parents must be carriers for the same genetic disorder to be at risk for having an affected child," says Shires. If only one parent carries the gene, then the baby might end up being a carrier, but they will not end up with the disorder. These conditions include cystic fibrosis, sickle cell disease, Tay–Sachs disease, and muscular dystrophy.

Some genetic disorders are more common in certain ethnic groups and/or run in families. Depending on your background, your healthcare provider or genetic counselor may recommend some conditions be screened for these reasons. This is called targeted carrier screening. When screening is done that isn't linked to a specific ethnicity or reason putting you at higher risk, this is often called expanded carrier screening. You may choose either option or a combination of both.

X-Linked Inheritance

Additionally, a small number of disorders on carrier screening panels follow X-linked inheritance. "In X-linked inheritance, the genetic variant is linked to the X-chromosome and is typically passed primarily from women to sons. One exception is fragile X syndrome which can be passed from women to sons or daughters," explains Shire.

Note that carrier screening technology is improving and changing quickly, says Feist. "The conditions we test for and the ability to detect the disorders is rapidly changing." Plus, new treatments for these disorders are also continually in development. Your genetic counselor can provide the latest information to you on what is available.

What Happens If You Test Positive for a Condition? 

Testing positive for being a carrier of a genetic disorder does not mean that your future baby will get a certain genetic disorder. Rather getting positive results lets you know if you are a carrier of the tested condition and can help you understand what the odds are that you may pass it on to your child, explains Elfmann.

"In most cases being a carrier for a genetic disorder does not cause an individual any health concerns. Thus, most people are unaware that they are carriers. Also, most carriers have no family history of the genetic disorder," explains Shires. For most people, finding out that they are a carrier is a big surprise.

How Genetic Inheritance Works

When someone tests positive for being a carrier, follow-up carrier screening is recommended for their reproductive partner to determine the risk of having an affected pregnancy. If that person tests negative, then the baby is most likely not at risk of developing the condition. "For genetic disorders that follow recessive inheritance, a couple is only at risk to have an affected child with a genetic disorder if they are both carriers for the condition," says Shire.

Note, however, that it is still possible for a baby to end up with a genetic disorder even if neither or only one parent tests positive for the genetic variant. While very rare, this is possible because carrier screening is not 100% accurate and may miss some instances of a person carrying the genes for a specific disorder, explains Elfman. Additionally, it is also possible for the baby to have a different genetic disorder that wasn't tested for.

However, in most cases, if both parents test negative or only one tests positive, then the baby will not have the genetic disorder. However, they have a 50% chance of being a carrier themselves. "If both parents are carriers for the same recessive genetic disorder, there is a 25% chance with each pregnancy that a child would be affected," explains Shire.

Testing is done first on the person who will be (or is) carrying the baby. If that person's results are negative, meaning they do not carry the genetic variations tested for, then no testing is needed from their partner. These disorders can only pass on to the future baby if both partners are carriers. So, even if the other person carries a gene for a genetic disorder, it will not trigger the condition in the baby. If the intended pregnant person's results are positive, then their partner may be tested.

"Genetic counseling is recommended for carrier individuals or couples to discuss options for testing and treatment for affected pregnancies and children," says Shire. If it is determined that a fetus does have a genetic condition, there may be interventions available to reduce the impact on the child. Knowing this information before birth also gives the parents and their health team time to prepare. Additionally, termination of the pregnancy may be considered.

If carrier information is obtained pre-pregnancy, the option of achieving a pregnancy with in vitro fertilization with pre-implantation genetic testing may also be available for carrier couples, says Shire. Using this method, experts will screen the embryos to ensure that only healthy ones are implanted for pregnancy.

"It's important to note that being a carrier is very common," says Elfman. In fact, says Elfmann, most people will find a genetic variation if enough testing is done. Most often, these mutations do not cause any harm.

Being a carrier is nothing to feel bad about and does not mean you did anything wrong. And in most cases, does not have an impact on the individual’s personal health. However, occasionally, being a carrier may cause mild symptoms or put you at higher risk of developing other medical conditions. Your healthcare provider or genetic counselor will discuss these issues with you and can answer any questions you have.

A Word From Verywell

Carrier screening is a type of genetic testing that can give prospective or pregnant individuals more information about the potential genetic risks to their pregnancy and future baby. Pre and post-test genetic counseling can help people decide what they want to test for and fully understand the specifics of the genetic conditions they are screening for and what their results mean. Discuss your options and any concerns or questions you have with your healthcare provider.

2 Sources
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  1. The American College of Obstetricians and Gynecologists. Carrier screening.

  2. The American College of Obstetricians and Gynecologists. Carrier screening for genetic conditions.