The goal of carrier screening is to provide individuals and couples information about their risk of having a child with an inherited disorder. With preconception carrier screening, individuals and couples found to be at risk for inherited conditions can consider reproductive options. During pregnancy, carrier screening allows for the option of diagnostic testing, informed decision-making, and preparation for a child with an inherited condition. Screening may be approached sequentially, where one partner is screened first and the second partner's screening is determined by those results, or concurrently, where full screening takes place for both partners at the same time.

Small, targeted panels often range from three or four conditions up to a few dozen conditions, focusing on a core group of conditions that are relatively common in the general population or more common in individuals from certain ethnicities or ancestries.

Large carrier screening panels include a range of conditions, including some conditions that are very rare or have mild or adult-onset of symptoms. Screening is panethnic, as all patients receive the same test regardless of self-reported race or ancestry. The larger the carrier screening panel, the more carriers will be identified, leading to the need for more post-test counseling, partner testing, and the option of diagnostic testing with tests such as amniocentesis. Due to the size of carrier screening panels now available, it is important to recognize the benefits and limitations of different types of tests in order to help patients identify the best test for them and to aid in interpretation of the results as they apply to the patient.

In these cases, you will practice:

• weighing the benefits and limitations of different carrier screening options for patients with different goals and concerns
• interpreting positive and negative carrier screening results.

Provider roles in test selection

The health care provider plays an important role in helping the patient identify their goals and exploring whether and what kind of screening best meets their individual needs. It is not necessary to discuss every potential outcome or source of uncertainty, but a general overview of benefits and limitations of different approaches is important. Providers also help patients navigate the scope of the test.

Targeted panels generally include well-described and common conditions such as cystic fibrosis, spinal muscular atrophy, hemoglobinopathies, and in some cases, fragile X and screening for conditions with increased prevalence in the Ashkenazi Jewish population.

Large panels screen for hundreds of conditions, both common and rare. Large panels have a greater detection rate for genetic disease but also additional limitations and risks.

Benefits 

Carrier screening can provide reassurance or actionable information for reproductive decision-making, consideration of prenatal diagnostic testing, planning, and preparation for a child with special needs, or early medical intervention.

Limitations

A negative screen reduces but does not eliminate the chance of the fetus being affected by a genetic condition. This is because screening does not capture every genetic change associated with disorders.

Carrier testing can introduce uncertainty if the father or donor is unavailable or unwilling to undergo screening and the patient screens positive.

Carrier screening is often linked to a patient's willingness to do diagnostic testing. This is an important conversation to have while determining what, if any, approach to carrier screening is best for a specific patient. Some couples may find it useful to have risk information even when they would not consider confirmatory diagnostic testing such as amniocentesis.

Interpreting results

The results of carrier screening can provide valuable information but may also produce some surprises for patients and providers alike.

A negative screening result can be reassuring, but the patient and provider should clearly understand the limits of that reassurance. When uncertainty remains, consider collaboration with the laboratory or a genetic expert to help interpret results and determine the best next steps.

A positive screening result can inform reproductive decision-making and facilitate additional testing, interventions, or help plan for a child with special needs. Keep in mind that:

• A positive result is not always actionable.
• Rare variants with variable or unknown disease expression can complicate decision-making.
• Patients and providers may be conflicted about whether risk for mild or adult-onset conditions warrants follow-up.
• Carrier screening can result in unanticipated findings, such as a diagnosis of a parent, that are unrelated to reproductive decision-making.

Consultation with genetic experts can be helpful before and after carrier screening. They can facilitate patient decision-making, assist in results interpretation and provide genetic counseling and emotional support throughout the screening process.