Screening estimates chance; diagnosis answers a narrower question
Carrier screening identifies people with a pathogenic or likely pathogenic variant for an autosomal-recessive or X-linked condition, usually without symptoms themselves. Prenatal screening estimates the chance of selected fetal conditions. Diagnostic tests such as chorionic-villus sampling or amniocentesis analyse fetal material more directly. Preimplantation genetic testing analyses embryos created through IVF for a defined indication.
These tests are not interchangeable. A positive cell-free DNA screen should be followed by genetic counselling and an offer of diagnostic testing rather than treated as a fetal diagnosis [1]. Carrier screening does not test for all genetic disease, de novo variants or every variant within included genes. A negative result reduces risk but leaves residual risk [2].
- Ask whether the result is screening or diagnostic.
- Confirm the condition, gene, variant and laboratory method.
- Do not make irreversible decisions from a screening result alone.
Preconception offers the widest set of options
ACMG recommends a consistent, equitable offer of pan-ethnic carrier screening before or during pregnancy and prefers preconception screening because it allows more time and reproductive options [2]. ACOG considers ethnic-specific, pan-ethnic and expanded approaches acceptable when applied consistently with counselling [3]. Ancestry still matters for interpretation, but appearance or a broad racial label is an unreliable substitute for family history and validated testing.
If one partner is a carrier for an autosomal-recessive condition, the reproductive partner can be offered testing. When time is limited in pregnancy, concurrent testing may be appropriate. If both carry pathogenic variants in the same recessive gene, counselling can cover natural conception, prenatal diagnosis, IVF with PGT-M, donor gametes, adoption or choosing not to pursue pregnancy. The counsellor supports values-based choice rather than directing one outcome.
- Offer screening before pregnancy when possible.
- Revisit carrier screening if the reproductive partner changes.
- Explain cost, timing and what is not included before collecting a sample.
Variant interpretation is the clinical work
Laboratories classify variants as pathogenic, likely pathogenic, uncertain significance, likely benign or benign using evolving evidence. A variant of uncertain significance does not establish that a condition will occur and should not be used for predictive testing in relatives or embryo selection as though it were pathogenic. Reclassification can occur, so the report date, laboratory and contact plan matter.
Penetrance describes how often a genotype is associated with a phenotype; expressivity describes how features vary. Some conditions have uncertain or variable outcomes, which makes counselling more complex. The result should be interpreted with phenotype, family history and test limitations. Raw-data interpretation from consumer services may produce false positives and should be clinically confirmed before care changes [4].
- Request the laboratory's evidence and classification date.
- Confirm clinically actionable consumer findings in an accredited laboratory.
- Create a route for recontact when classification changes.
PGT reduces a defined risk but does not guarantee a healthy child
PGT-M can test embryos for a known single-gene condition, while PGT-SR addresses certain structural chromosome rearrangements. PGT-A estimates chromosome copy number and has different indications and evidence. Embryo biopsy, amplification and mosaic results introduce uncertainty. Professional guidance recommends discussing confirmatory prenatal diagnosis after PGT because testing samples a small number of placental-lineage cells rather than the fetus directly [5].
Success also depends on ovarian response, fertilisation, embryo development, the number of informative embryos, maternal age and laboratory performance. A pathway should report outcomes per cycle started and live birth, not only the percentage of embryos successfully tested. Legal rules on embryo testing and selection differ internationally and can affect which options are available.
- Clarify which PGT type is proposed and why.
- Ask how no-result and mosaic results are managed.
- Discuss prenatal confirmation and residual risk before embryo transfer.
Genetic information belongs to a family and a person
A result can matter to siblings, parents and future children, yet the tested person retains privacy and choice. NCI and ACOG both emphasise informed consent, family implications and protection of genetic information [4][6]. Counselling should discuss family communication, consanguinity where relevant, insurance or legal concerns in the local jurisdiction and emotional impact. Consent should separate clinical testing from optional research or broad data sharing.
Digital pedigrees and decision tools can reduce omissions, but they can also expose adoption, donor conception, non-paternity or sensitive diagnoses. Systems need granular access, correction, family-link management and clear retention rules. The quality metric is informed decision making with documented understanding, not the largest panel or the highest testing rate.
- Collect only family details relevant to the clinical question.
- Explain who can see results and whether relatives can be contacted.
- Provide a plain-language report that remains useful across care settings.
What the evidence cannot yet answer
- Carrier panels differ in genes, variant coverage and residual-risk estimates, so a negative result is not universal reassurance.
- Variant interpretation changes as evidence develops, and variants of uncertain significance are not clinically predictive.
- PGT samples a few embryo cells and does not guarantee implantation, live birth or absence of every condition.
Questions worth taking into care
- Is this a screening or diagnostic test, and what exact conditions does it assess?
- What residual risk remains after a negative result?
- How would positive, uncertain and no-result findings change options?
- If PGT is proposed, what are outcomes per cycle started and is prenatal confirmation advised?
- How will clinically important reclassification or family implications be communicated?
Source record
Evidence used in this review
Sources were selected for clinical authority, methodological relevance and traceability. Links open the original guidance, public-health record or research publication.
- [1]Screening for Fetal Chromosomal Abnormalities
American College of Obstetricians and Gynecologists · 2026
- [2]Screening for Autosomal Recessive and X-Linked Conditions During Pregnancy and Preconception
American College of Medical Genetics and Genomics · 2021
- [3]Carrier Screening in the Age of Genomic Medicine
American College of Obstetricians and Gynecologists · 2017
- [4]Genetic Testing Fact Sheet
National Cancer Institute · 2024
- [5]Preimplantation Genetic Testing
American College of Obstetricians and Gynecologists · 2020
- [6]Ethical Considerations for Genetic Testing and Counseling in Obstetrics and Gynecology
American College of Obstetricians and Gynecologists · 2026
This evidence synthesis is for general information. It does not diagnose a condition or replace care from a qualified health professional. Treatment choices depend on individual history, examination, local guidance and informed preference. Emergency or rapidly worsening symptoms need urgent local medical assessment.