Paeds Vivas · genetics-dysmorphology-and-metabolism
Prenatal diagnosis and reproductive genetics — branching viva
Branching viva from a positive cell-free DNA screen through microarray interpretation, variant of uncertain significance reasoning, consanguinity and PGT-M counselling, and the paediatrician's role in translating genotype to postnatal plan.
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Target exams
RACP General PaediatricsRACP DCEMRCPCH ClinicalRCPSC Pediatrics
Prompt
You are the paediatric registrar on the fetal medicine multidisciplinary round. A patient has a positive cell-free DNA screen. The examiner releases information in stages about diagnostic testing, microarray interpretation, variant of uncertain significance reasoning, consanguinity and reproductive options, and the paediatrician's planning role.
Station opening
Examiner: "The cell-free DNA screen is positive for trisomy 21 at high probability. The patient asks whether the baby has Down syndrome. What do you say?" [3]
Strong candidate (must-hit)
- A positive cfDNA screen is a screen, not a confirmed diagnosis. It raises probability and warrants counselling and an offer of diagnostic testing (CVS or amniocentesis by gestation). [3]
- Separates screening from diagnosis explicitly and states that confirmation is needed before any management decision. [3]
- Quotes contemporary, not legacy, procedure-related miscarriage risk for the diagnostic procedure. [4]
Weak candidate
- "Your baby has Down syndrome." [3]
- Offers a repeat cfDNA screen instead of diagnostic testing when pre-test probability is high. [3]
References7ShowHide
- [1]Wapner RJ, Martin CL, Levy B, et al. Chromosomal microarray versus karyotyping for prenatal diagnosis. The New England journal of medicine, 2012.PMID 23215555
- [3]Norton ME, Jacobsson B, Swamy GK, et al. Cell-free DNA analysis for noninvasive examination of trisomy. The New England journal of medicine, 2015.PMID 25830321
- [4]Salomon LJ, Sotiriadis A, Wulff CB, et al. Risk of miscarriage following amniocentesis or chorionic villus sampling: systematic review. Ultrasound in obstetrics & gynecology, 2019.PMID 31124209
- [6]Stosic M, Levy B, Wapner R. The use of chromosomal microarray analysis in prenatal diagnosis. Obstetrics and gynecology clinics of North America, 2018.PMID 29428286
- [7]American College of Obstetricians and Gynecologists. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin Summary, Number 226. Obstetrics and gynecology, 2020.PMID 32976375
- [8]Spinella F, Bronet F, Carvalho F, et al. ESHRE PGT Consortium data collection XXI: PGT analyses in 2018. Human reproduction open, 2023.PMID 37091225
- [11]Lord J, McMullan DJ, Eberhardt RY, et al. Prenatal exome sequencing in congenital heart disease (CODE) study. Ultrasound in obstetrics & gynecology, 2021.PMID 32388881