Genetic counseling principles

Indications - Who Gets a Consult?

• Advanced Maternal Age (AMA): Age ≥35 at estimated date of delivery.
• Abnormal Screening Results: Positive findings on aneuploidy screens (e.g., cfDNA, quad screen) or ultrasound markers (e.g., ↑ nuchal translucency).
• Family History: Personal or family hx of a known genetic disorder, birth defect, or intellectual disability.
• Previous Affected Pregnancy: History of a prior child with a chromosomal or genetic condition.
• Teratogen Exposure: Significant exposure to medications, radiation, or infections linked to birth defects.
• Consanguinity: Parents are related by blood.

⭐ High-Yield: Advanced Maternal Age (AMA) is the most frequent referral indication, driven by the age-related ↑ risk for fetal aneuploidies like Down syndrome.

Counseling Core - The Guiding Rules

• Patient-Centered Approach: Focus on patient values, beliefs, and goals.
• Non-Directive Counseling: Empower patients to make informed decisions that align with their own values. The counselor facilitates, but does not direct, patient choices.
• Informed Consent: A critical process, not just a form. Ensures patient understands the risks, benefits, limitations, and alternatives of genetic testing.
• Confidentiality: Uphold strict patient privacy regarding sensitive genetic information.
• Psychosocial Support: Address emotional responses (e.g., anxiety, guilt) and family dynamics.

⭐ High-Yield Fact: The primary role of a genetic counselor is to provide information and support, not to recommend a specific course of action. Recommending termination or continuation of a pregnancy is inappropriate.

Testing Toolkit - Screen vs. Diagnose

• Screening Tests: Assess Risk

  • Non-invasive or minimally invasive methods to identify pregnancies at ↑ risk for aneuploidy.
  • They do not diagnose; they provide a risk probability (e.g., 1 in 1,000).
  • Examples:
    • Cell-free DNA (cfDNA): Highest detection rate for common trisomies.
    • First Trimester Combined Screen: PAPP-A, β-hCG, nuchal translucency (NT).
    • Quad Screen: AFP, estriol, β-hCG, inhibin A.

• Diagnostic Tests: Confirm Diagnosis

  • Invasive procedures offering a definitive yes/no answer.
  • Carry a small risk of pregnancy loss (~1 in 300-500).
  • Indicated after a positive screening test or for high-risk patients.
  • Examples:
    • Chorionic Villus Sampling (CVS): 10-13 weeks.
    • Amniocentesis: After 15 weeks.

⭐ A positive screening test result does not diagnose a fetal condition. It indicates that the risk is high enough to warrant offering definitive diagnostic testing (CVS or amniocentesis) for confirmation.

The Results Reveal - Now What?

• Positive Screen: Not a diagnosis. Indicates ↑ risk, prompting the offer of definitive diagnostic tests.
• Negative Screen: Low probability of the condition. Reassurance is provided; typically, no further aneuploidy testing is needed.
• Counseling is Key: Discuss the positive predictive value (PPV), limitations of screening, and options for diagnostic testing (including risks/benefits). Patient autonomy is paramount.

⭐ Timing is critical for diagnostic choice: Chorionic Villus Sampling (CVS) is performed at 10-13 weeks, allowing for earlier diagnosis. Amniocentesis is performed later, typically after 15 weeks gestation.

High‑Yield Points - ⚡ Biggest Takeaways

• The cornerstone is non-directive counseling; provide information and options, but the patient makes the final decision.
• Always obtain informed consent before any genetic testing, respecting patient autonomy.
• Key indications: advanced maternal age (AMA >35), abnormal screening, and positive family history.
• Clearly distinguish between screening tests (assess risk) and diagnostic tests (e.g., amniocentesis, CVS) which are definitive.
• Address patient emotions and maintain strict confidentiality.