Is Expanded Carrier Screening Standard of Care for Pregnant Patients?
Yes, expanded carrier screening (ECS) is now considered standard of care for all pregnant patients and those planning pregnancy, with the American College of Medical Genetics and Genomics (ACMG) specifically recommending that tier 3 carrier screening (covering 97 autosomal recessive and 16 X-linked conditions with carrier frequencies ≥1/200) should be offered to all pregnant patients. 1, 2
Current Guideline Recommendations
The ACMG's 2024 technical standard represents the most authoritative and recent guidance on this question, establishing a clear framework for carrier screening:
All pregnant patients should be offered tier 3 carrier screening, which includes conditions with carrier frequencies of at least 1 in 200, encompassing 97 autosomal recessive genes and 16 X-linked genes including Duchenne muscular dystrophy and Fragile X syndrome 1
Tier 3 screening includes mandatory tier 1 conditions (cystic fibrosis, spinal muscular atrophy, and risk-based screening) that form the foundation of carrier screening 1, 2
The tiered approach facilitates communication between patients and providers about the extent of screening that may have already occurred in prior pregnancies or fertility evaluations 1
Shift from Ethnicity-Based to Pan-Ethnic Screening
The standard of care has evolved from targeted ethnicity-based screening to universal expanded carrier screening for all patients:
ACMG recommends a pan-ethnic approach rather than limiting testing to specific ethnic groups, as many carriers do not report ancestry traditionally associated with certain genetic conditions 2
The National Society of Genetic Counselors (2023) explicitly recommends ECS be made available for all individuals considering reproduction and all pregnant reproductive pairs, noting that ECS is superior to ethnicity-based screening because it identifies more carriers and eliminates race-based medical practice 3
Ethnic-specific, panethnic, and expanded carrier screening are all acceptable strategies, but each practice should establish a standard approach consistently offered to all patients, ideally before pregnancy 4
Clinical Rationale Supporting Standard of Care Status
The evidence supporting ECS as standard of care is based on multiple factors:
ECS identifies significantly more at-risk couples compared to ethnicity-based approaches, with 77% of couples screened preconceptionally planning or pursuing actions to avoid having affected offspring 5
The technology now enables simultaneous screening for dozens to hundreds of diseases with low cost, high-throughput capabilities, and rapid turnaround times 1
ECS provides meaningful information that patients can use to guide pregnancy planning based on their personal values, with the goal of allowing individuals to consider their full range of reproductive options 4
Optimal Timing and Sequential Testing Approach
When implementing carrier screening, timing and sequence matter:
Preconception screening is strongly preferred because it allows consideration of all reproductive options including preimplantation genetic diagnosis, donor gametes, or adoption 6, 7
Sequential testing is recommended: the woman should be screened first, and if positive for an autosomal recessive disorder, the male partner should then be tested 6
Critical timing caveat: If screening cannot be completed before conception, initiate as early as possible in pregnancy 6, 7
After 14 weeks gestation, both partners should be tested concurrently rather than sequentially due to time constraints for decision-making 6, 7
What Conditions Are Included
The tier 3 panel recommended as standard of care includes:
- Cystic fibrosis (CFTR gene) 1, 2
- Spinal muscular atrophy 1, 2
- Conditions with carrier frequencies ≥1/200 in the general population 1
- Selected X-linked conditions including Duchenne muscular dystrophy and Fragile X syndrome 1
- For Ashkenazi Jewish populations, specific conditions like Tay-Sachs, Canavan disease, Gaucher disease, and familial dysautonomia remain important 1, 2
Common Pitfalls to Avoid
Several critical considerations when implementing ECS:
Do not wait until pregnancy is established to initiate carrier screening discussions, as the preconception period provides the widest range of reproductive options and avoids time pressure and emotional stress 6
Do not assume ethnicity-based screening is sufficient in the current era, as the marked ethnic admixture in the United States makes it difficult to classify or exclude patients based on ethnic group 1
Counsel patients about residual risk with any test result, as carrier screening will not identify all individuals at risk of screened conditions 4
Recognize that screening is optional: after counseling, a patient may decline any or all carrier screening, and if a patient requests a different screening strategy, it should be made available after counseling on limitations, benefits, and alternatives 4
Practical Implementation
For clinical practice, the following algorithm applies:
Offer tier 3 expanded carrier screening to all pregnant patients and those planning pregnancy, regardless of ethnicity 1, 2
Screen the woman first (ideally preconceptionally), then test the male partner only if she tests positive for an autosomal recessive condition 6
If both partners are carriers of the same condition, provide genetic counseling and offer prenatal diagnosis or discuss preconception options if not yet pregnant 1, 6
Report all pathogenic/likely pathogenic variants in tier 3 genes 1
Refer to genetics specialists for risk assessment when family history suggests genetic conditions or when complex results require interpretation 4
The evidence clearly supports that expanded carrier screening has transitioned from an optional test to standard of care, with the most recent and authoritative guidelines from ACMG (2024) establishing tier 3 screening as the recommended approach for all pregnant patients and those planning pregnancy.