Most people who carry a gene variant for a serious inherited condition have no idea. Carriers of autosomal recessive conditions like cystic fibrosis, spinal muscular atrophy, or Tay-Sachs disease are typically healthy — the condition only appears when two carriers of the same condition have a child together. That 25% chance of an affected pregnancy is invisible until it happens.
Preconception genetic carrier screening exists to change that dynamic. By testing prospective parents before or early in pregnancy, couples gain the information they need to understand their reproductive risk, consider available options, and make decisions that align with their values.
This guide covers everything about preconception genetic testing: the difference between expanded and targeted carrier screening, what conditions are included, what to do when both partners are carriers, PGT-M as a reproductive option, cost comparison, and what ACOG, ACMG, and other professional bodies recommend.
What Is Carrier Screening?
A carrier is a person who has one working copy and one non-working copy of a gene that, when both copies are non-functional, causes a specific inherited condition. Carriers themselves are typically unaffected.
Autosomal recessive inheritance is the most common pattern for conditions screened preconceptionally:
- Each parent carries one variant (carrier status)
- Each pregnancy has a 25% chance of inheriting both variants (affected)
- Each pregnancy has a 50% chance of being a carrier (like the parents)
- Each pregnancy has a 25% chance of inheriting two normal copies
X-linked recessive conditions (like fragile X-associated conditions) work differently — female carriers have a 50% chance of passing the variant to each child, with sons more likely to be affected.
Expanded Carrier Screening vs. Targeted Screening
Two approaches exist, and the distinction matters for both coverage and clinical decision-making.
Targeted (Ethnicity-Based) Screening
Traditional approach. Tests for a small set of conditions most prevalent in specific ethnic groups:
| Ethnicity | Conditions Typically Screened |
|---|---|
| Ashkenazi Jewish | Tay-Sachs, Canavan disease, familial dysautonomia, Gaucher, cystic fibrosis |
| African American | Sickle cell disease, cystic fibrosis, alpha-thalassemia |
| Mediterranean | Beta-thalassemia, sickle cell |
| East Asian | Alpha-thalassemia |
| General population | Cystic fibrosis (CF), spinal muscular atrophy (SMA) |
Limitation: Multi-ethnic individuals may not clearly fit one category. Self-identified ethnicity doesn't capture the full complexity of genetic ancestry. Studies show targeted screening misses a significant percentage of at-risk couples — particularly as global populations become more admixed.
Expanded Carrier Screening (ECS)
Modern approach. Tests for 200–500+ conditions simultaneously regardless of ethnicity, using a single blood or saliva sample. Conditions included typically span:
- Severe early-onset diseases (e.g., Tay-Sachs, SMA, cystic fibrosis)
- Milder or later-onset conditions (varies by panel)
- Conditions with available treatment vs. those without
- Conditions where prenatal diagnosis is actionable
ACMG (2021 ECS guideline) recommends a tiered approach: every prospective parent should be offered ECS for Tier 1 conditions — defined as conditions with a carrier frequency >1/200 in the general population AND residual risk <1/100 after a negative screen AND severe childhood onset. Currently, approximately 113 conditions meet Tier 1 criteria.
ACOG Committee Opinion 690 (reaffirmed) recommends offering expanded carrier screening to all patients who are pregnant or considering pregnancy, regardless of ethnicity — because the majority of affected children are born to parents with no known family history.
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Conditions Included in Expanded Carrier Screening
Modern ECS panels typically screen for 200–500 conditions. The most clinically important include:
| Condition | Inheritance | Carrier Frequency | Severity |
|---|---|---|---|
| Cystic fibrosis | Autosomal recessive | ~1 in 25 (Caucasian) | Severe; progressive lung and GI disease |
| Spinal muscular atrophy (SMA) | Autosomal recessive | ~1 in 40–50 | Severe; progressive motor neuron loss |
| Fragile X (FMR1 premutation) | X-linked | ~1 in 151 females | Intellectual disability, autism spectrum features |
| Sickle cell disease | Autosomal recessive | ~1 in 12 (African American) | Severe; vaso-occlusive crises, organ damage |
| Beta-thalassemia | Autosomal recessive | ~1 in 25 (Mediterranean) | Severe anemia; transfusion dependence |
| Tay-Sachs disease | Autosomal recessive | ~1 in 30 (Ashkenazi Jewish) | Fatal; progressive neurological deterioration |
| Gaucher disease | Autosomal recessive | ~1 in 15 (Ashkenazi Jewish) | Variable; Type 1 treatable |
| Phenylketonuria (PKU) | Autosomal recessive | ~1 in 50 | Severe if untreated; manageable with diet |
| MCAD deficiency | Autosomal recessive | ~1 in 40 | Metabolic emergency; treatable with early detection |
| Pompe disease | Autosomal recessive | ~1 in 100 | Severe cardiac and muscular involvement |
Panels from major commercial labs (Invitae, Natera Horizon, Myriad Foresight, Counsyl/now Myriad) differ in the number of conditions screened and the number of variants tested per condition. More variants tested generally means higher sensitivity but potentially more uncertain variants of unclear significance.
Cascade Testing: When One Partner Tests First
Cascade testing refers to the sequential testing strategy where one partner is tested first, and the second partner is only tested for the specific conditions in which the first is found to be a carrier.
This approach:
- Reduces cost for couples who will only act on a "both positive" result
- Introduces a delay of 1–2 weeks for sequential results
- May miss conditions where the first partner tested negative by chance
Alternatively, both partners can be tested simultaneously — the most efficient approach for couples who want results quickly or are already in fertility treatment.
If using donor sperm or donor eggs, the clinic will typically check that the donor has been carrier screened. If the donor is a carrier for a condition, the recipient should be tested for that same condition before proceeding.
What to Do If Both Partners Are Carriers for the Same Condition
The discovery that both partners carry variants in the same gene — making them an at-risk couple — is alarming to receive but is actually actionable information. You have several evidence-based options.
Option 1: Conceive Naturally and Pursue Prenatal Testing
Chorionic villus sampling (CVS) at 10–13 weeks or amniocentesis at 15–20 weeks can diagnose whether the fetus inherited the condition. Depending on the result and your values, you may continue the pregnancy or consider termination.
This is a valid option, but it involves conceiving, waiting, testing, and potentially receiving a difficult result mid-pregnancy.
Option 2: IVF with PGT-M (Preimplantation Genetic Testing — Monogenic)
PGT-M (formerly called PGD) is the most proactive option. It involves:
- Undergoing IVF to create embryos
- Performing a biopsy on each blastocyst (day 5–6 embryo)
- Sending the biopsied cells to a specialized genetics lab for disease-specific testing
- Transferring only embryos that did not inherit both disease variants
PGT-M requires a custom probe design specific to the couple's variants, which takes 4–12 weeks to prepare before the IVF cycle. Not all variants are amenable to PGT-M — your genetic counselor will confirm feasibility.
PGT-M:
- Identifies unaffected embryos before transfer, eliminating the need for invasive prenatal testing
- Does not guarantee a healthy pregnancy (chromosomal abnormalities are not covered unless PGT-A is added)
- Adds $3,000–$6,000 to the cost of an IVF cycle for probe design and testing
- Requires IVF — not appropriate for couples who object to IVF or embryo disposal
Option 3: Use Third-Party Gametes
If a couple is both carriers for the same condition, one option is to use donor sperm or donor eggs from a donor who has been screened and confirmed negative for that condition. This eliminates the risk entirely for that condition but uses gametes from a third party.
Option 4: Adopt or Use Gestational Carrier
Some couples may choose not to use their own genetic material for conception. Adoption or embryo donation (from another couple's unused IVF embryos) are paths available regardless of genetic status.
Option 5: Conceive Naturally Without Testing
Some couples — for religious, philosophical, or personal reasons — choose to conceive without pursuing prenatal diagnosis or PGT-M. This is a personal decision and should be respected; genetic counseling ensures it is informed.
Genetic Counseling: Who You Need on Your Team
Any couple with a positive carrier screening result indicating they are at risk should be referred to a board-certified genetic counselor. Genetic counselors provide:
- Detailed explanation of the specific condition and inheritance pattern
- Discussion of reproductive options in the context of the couple's values
- Review of carrier testing results and residual risk after a negative screen
- Coordination of PGT-M probe design if IVF is chosen
- Support for complex decisions
Genetic counseling is covered by most insurance plans for patients with a positive carrier screen result.
Cost Comparison: ECS Testing Options
| Option | Cost Range | Notes |
|---|---|---|
| Targeted carrier screen (3–5 conditions) | $0–$150 with insurance | Limited conditions; may miss at-risk couples |
| Expanded carrier screen (200–500 conditions) | $100–$400 self-pay | Often $0–$50 with insurance; major labs: Invitae, Natera, Myriad |
| Direct-to-consumer (23andMe health) | $199–$229 | Very limited conditions; not for clinical decision-making |
| IVF + PGT-M (if indicated) | +$3,000–$6,500 on top of IVF cost | Required for at-risk couples pursuing IVF |
| Prenatal diagnosis (CVS or amnio) | $1,000–$3,000 out-of-pocket | Invasive; diagnoses rather than prevents |
Direct-to-Consumer Testing Limitations
Consumer tests like 23andMe include a handful of carrier screening results (CF, SMA, BRCA, etc.) but test a very limited subset of variants. A "negative" result on 23andMe does not rule out carrier status for most conditions — and results should never replace clinical carrier screening before attempting pregnancy.
ACOG and ACMG Recommendations
| Organization | Recommendation |
|---|---|
| ACOG (Committee Opinion 690, 2017) | Offer ECS to all patients considering pregnancy, regardless of ethnicity |
| ACMG (ECS Guideline 2021) | Offer Tier 1 ECS to all; standardize panels around conditions meeting criteria for severity, frequency, and actionability |
| ASRM | Carrier screening for CF and SMA before IVF; ECS recommended for comprehensive evaluation |
| NSGC | ECS is the preferred approach over ethnicity-based screening |
The shift to universal ECS — endorsed by all major professional societies — reflects evidence that ethnicity-based testing misses a substantial proportion of at-risk couples in an increasingly diverse population.
Fragile X: A Special Case
Fragile X syndrome is caused by an expansion of a CGG repeat sequence in the FMR1 gene on the X chromosome. The FMR1 premutation is the carrier state — carriers have 55–200 repeats and are generally unaffected, but their children can inherit a full mutation (>200 repeats), which causes intellectual disability and behavioral challenges.
Fragile X screening is particularly important for women because:
- Premutation carriers are at risk for premature ovarian insufficiency (POI) — loss of ovarian function before age 40
- Premutation carrier females should be counseled about fertility urgency and egg freezing
- Female premutation carriers may have emotional and cognitive challenges of their own (FXTAS later in life)
ACOG recommends offering fragile X carrier testing to women with a personal or family history of unexplained intellectual disability, developmental delay, autism, or premature ovarian insufficiency.
Who Should Be Tested and When
Ideal timing: Before pregnancy — preconception testing provides maximum time to understand results, seek genetic counseling, and make reproductive decisions without time pressure.
Minimum timing: Early in the first trimester of pregnancy — sequential testing is still possible, but options are compressed.
Who should be tested:
- All individuals planning pregnancy (ECS is universally recommended)
- Individuals with a personal or family history of a genetic condition
- Individuals with a partner who is known to be a carrier
- Individuals using donor gametes (to confirm donor compatibility)
- All patients entering IVF regardless of personal history
Key Takeaways
- Expanded carrier screening (ECS) tests 200–500+ conditions in a single blood or saliva sample and is recommended for all prospective parents regardless of ethnicity
- Carriers are typically healthy; the risk only emerges when both partners carry variants in the same gene
- If both partners are carriers for the same condition, options include natural conception + prenatal testing, IVF + PGT-M, or use of donor gametes
- PGT-M identifies unaffected embryos before transfer but adds $3,000–$6,500 to IVF costs and requires custom probe design
- Genetic counseling is essential for any at-risk couple
- Consumer genetic tests (23andMe) are not substitutes for clinical carrier screening
- ACOG and ACMG recommend offering ECS to all patients considering pregnancy
References
- American College of Medical Genetics and Genomics (ACMG). Expanding the spectrum of conditions for carrier screening: update of the ACMG statement on population-based carrier screening. Genet Med. 2021;23(10):1800–1803.
- American College of Obstetricians and Gynecologists (ACOG). Committee Opinion No. 690: Carrier screening in the age of genomic medicine. Obstet Gynecol. 2017;129(3):e35–e40.
- Grody WW, Thompson BH, Gregg AR, et al. ACMG position statement on prenatal/preconception expanded carrier screening. Genet Med. 2013;15(6):482–483.
- Lazarin GA, Haque IS, Nazareth S, et al. An empirical estimate of carrier frequencies for 400+ causal Mendelian variants. Hum Genet. 2013;132(12):1319–1329.
Frequently Asked Questions
Q: What is the difference between expanded carrier screening and targeted carrier screening? A: Targeted screening tests for a small set of conditions most prevalent in specific ethnic groups (e.g., cystic fibrosis for Caucasians, sickle cell for African Americans). Expanded carrier screening (ECS) tests 200–500+ conditions simultaneously in a single blood or saliva sample, regardless of ethnicity. ACOG and ACMG both now recommend ECS for all patients considering pregnancy, because most affected children are born to parents with no known family history, and self-identified ethnicity doesn't capture the full complexity of genetic ancestry.
Q: What happens if both partners are carriers for the same condition? A: Being an at-risk couple (both carrying variants for the same gene) means each pregnancy has a 25% chance of an affected child. Your options include: conceiving naturally and pursuing prenatal testing (CVS or amniocentesis), pursuing IVF with PGT-M (preimplantation genetic testing for the specific condition — this identifies unaffected embryos before transfer), using donor gametes from a non-carrier, or conceiving naturally without testing. A board-certified genetic counselor is essential to guide this decision.
Q: What is PGT-M and how much does it cost? A: PGT-M (Preimplantation Genetic Testing for Monogenic conditions) involves IVF, blastocyst biopsy, and disease-specific testing of each embryo before transfer — only unaffected embryos are transferred. It requires a custom probe design specific to the couple's variants, which takes 4–12 weeks. PGT-M adds $3,000–$6,500 to the cost of an IVF cycle. It is the most proactive option for at-risk couples who want to avoid passing a specific condition.
Q: Is a consumer DNA test like 23andMe sufficient for preconception carrier screening? A: No. Consumer tests include only a small handful of carrier screening results, testing a very limited subset of variants. A "negative" result on 23andMe does not rule out carrier status for most conditions. ACOG and ACMG specifically state that consumer tests are not substitutes for clinical carrier screening before attempting pregnancy.
Q: What is fragile X syndrome and why does it require special attention for women? A: Fragile X syndrome is caused by an expansion of a CGG repeat in the FMR1 gene. Women who are premutation carriers (55–200 repeats) are at approximately 20% risk of premature ovarian insufficiency (POI) — loss of ovarian function before age 40. This is dramatically higher than the 1% general population risk. ACOG recommends offering fragile X carrier testing to women with unexplained intellectual disability, developmental delay, autism, or premature ovarian insufficiency in their personal or family history.
This article is for informational purposes only and does not constitute medical advice. Consult a board-certified genetic counselor and your reproductive endocrinologist for guidance on carrier screening and reproductive options.
