Prenatal and Reproductive Genetics
Screening versus diagnosis
Screening estimates probability; diagnosis confirms. Know the difference between maternal serum screening, cell-free DNA screening, and diagnostic tests (chorionic villus sampling, amniocentesis). Cell-free DNA is a screening test: a positive result requires diagnostic confirmation, and false positives occur, including from confined placental mosaicism and maternal factors. Candidates should know timing windows at a general level and that diagnostic testing carries a small procedure-related miscarriage risk that must be quoted accurately rather than minimized or exaggerated.
Reproductive options
Carrier couples may pursue prenatal diagnosis, preimplantation genetic testing, gamete donation, or accept risk. Counselling is nondirective and covers each option's practical and emotional demands. Preimplantation testing requires IVF and does not guarantee a pregnancy; results may be limited by mosaicism in embryos.
Traps
Questions often test the difference between "detects" and "diagnoses," the need for partner testing before interpreting a carrier result, and the fact that a normal screening result does not eliminate risk. Another trap is recommending termination or continuing a pregnancy; the counsellor supports the client's values. Also be alert to residual risk after negative carrier screening, which depends on the panel's detection rate for the client's ancestry.
Rule of thumb
Before discussing any prenatal result, ask what the client already understands and what decision, if any, they face. Example: a client with a high-risk cell-free DNA result asks, "So my baby has it?" The accurate response is that this is a screening result indicating increased chance, and diagnostic testing is needed to confirm; then explore what confirmation would mean for them.