Define Genetic Counselling & Prenatal Diagnosis. Describe its diagnosis and prevention.

Definition

• Genetic counselling is a communication process that helps a family understand a genetic condition — its diagnosis, natural history, recurrence risk and available options.
• It is non-directive, voluntary and confidential.

Indications

• A previous affected child or a family history of a genetic disorder.
• Consanguinity; advanced maternal age; recurrent pregnancy loss.
• An abnormal antenatal screening test or ultrasound; known carrier status (e.g. Thalassaemia).

Steps in Counselling

Establish an accurate diagnosis → Construct a pedigree → Estimate the recurrence risk (by inheritance pattern) → Communicate risks/options non-directively → Provide ongoing support

Recurrence Risk (examples)

• Autosomal recessive — 25% for two carrier parents.
• Autosomal dominant — 50% if a parent is affected.
• Chromosomal — depends on the type (e.g. Translocation Down syndrome differs from non-disjunction).

Prenatal Screening VS Diagnosis

Preventive Options

• Carrier screening and premarital/pre-pregnancy counselling (e.g. Thalassaemia).
• Prenatal diagnosis with informed reproductive choice; preimplantation genetic diagnosis in selected families.
• Folic acid to prevent neural-tube defects; avoidance of teratogens.

Ethical Principles

• Autonomy (the family decides), confidentiality, informed consent and a non-directive stance.
• Sensitivity around reproductive choices and disclosure within families.

Timing of Prenatal Tests

Prevention at Community Level

• Thalassaemia carrier screening and premarital counselling programmes (important in India).
• Periconceptional folic acid; rubella immunisation of girls; avoidance of teratogens/consanguinity awareness.

Nipt — Strengths & Limits

• Non-invasive prenatal testing (cell-free fetal DNA) screens for common trisomies (21, 18, 13) with high sensitivity from ~10 weeks.
• It is a screening test — a positive result must be confirmed by a diagnostic test (CVS/amniocentesis).

Support & Follow-up

Counselling continues after results — supporting the family through decisions, arranging specialist input for an affected pregnancy/child, and planning care and future reproductive options.

Preimplantation Genetic Diagnosis (PGD)

For couples at high risk of a specific single-gene or chromosomal disorder, PGD tests embryos created by IVF before implantation, allowing transfer of unaffected embryos — an option that avoids termination of an established pregnancy.

Carrier-screening Programmes (india)

• Thalassaemia carrier screening with premarital/antenatal counselling has reduced affected births in high-prevalence regions.
• Community education, and rubella immunisation of girls, are complementary preventive measures.

Common Screening Results (interpretation)

• Down syndrome — low PAPP-A, high β-hCG, increased nuchal translucency; low AFP on the quadruple test.
• Neural-tube defects — raised maternal serum AFP and confirmatory ultrasound.

Role in Prevention of Genetic Disease

Together, carrier screening, genetic counselling, prenatal diagnosis and (where appropriate) PGD form a preventive framework that — with folic acid supplementation and teratogen avoidance — reduces the burden of serious genetic and congenital disorders in the community.