Prenatal diagnosis — structured oral station (12 minutes)

Opening prompt — "What test would you offer?"

Model response: ^[3]

• "Because the fetus has a structural anomaly and the karyotype is normal, the right next test is chromosomal microarray, not a repeat karyotype."
• "Microarray looks at far higher resolution and finds copy-number variants — small deletions and duplications — that the karyotype cannot see."^[3]
• "It is done on amniotic fluid, which we already have, so she does not need another procedure."^[1]

Probe 1 — "How much more does microarray find?"

• "In the Wapner NEJM 2012 study of over 4400 samples, microarray found clinically relevant copy-number variants in an additional 6.0% of structurally abnormal fetuses with a normal karyotype. For a cardiac anomaly like this, that is a meaningful yield."^[3]

Probe 2 — "She is worried the amnio will cause a miscarriage. What do you tell her?"

• "The modern figure is reassuring. A 2019 meta-analysis put the procedure-related miscarriage risk at about 0.3% for amniocentesis above background, and close to zero in matched-risk studies. She has already had the amnio — the sample exists — so there is no additional procedure here."^[2]
• "I would not quote the old 1% figure; it overstates the risk."^[1][2]

Probe 3 — "Microarray is normal, but fetal exome sequencing returns a variant of uncertain significance. What do you do?"

• "Under the ACMG 2015 standard, a variant of uncertain significance is not acted upon as if it were pathogenic. I would refer to clinical genetics, offer parental segregation testing to help reclassify it, and counsel that it may be reclassified as evidence accumulates. I would not recommend termination on the basis of a VUS."^[5]

Probe 4 — "Does microarray ever miss something?"

• "Yes — two things. It does not detect balanced translocations, where chromosomal material is rearranged without net loss, and it does not detect triploidy. If either is suspected, we need a karyotype."^[3]

Probe 5 — "She is overwhelmed. Counsel her."

This is a scored domain. Demonstrate it out loud: ^[1]

• Move to her eye level, use her name, validate the overwhelm: "It is a lot, and we will take it step by step."
• Brief plainly: "We are looking at the baby's genes in fine detail. Some results are clear and some are uncertain, and our genetics team will explain every one. There is no rush, and no decision is needed today."
• Offer a written summary, a follow-up, and the genetic counsellor contact.^[1]