O&G SAQs · Antenatal care — fetal anomaly screening
Fetal structural anomalies — structured SAQ (15 marks)
FRANZCOG-format structured SAQ on the mid-trimester anatomy scan: the systematic ISUOG protocol and cardiac views, interpretation of an isolated echogenic focus against prior screening, the hyperechogenic-bowel differential, and the microarray referral pathway for a structural anomaly. Per-sub-part marking rubric included.
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Prompt
A 27-year-old woman at 20 weeks' gestation attends for her routine fetal anatomy scan. The sonographer reports an isolated echogenic intracardiac focus with an otherwise normal heart and normal anatomy; the woman had a low-risk cell-free DNA screen at 11 weeks. (a) Describe the systematic structure of the 18 to 20 week anatomy scan and the fetal cardiac views you expect to have been assessed. (5 marks) (b) Explain what an echogenic intracardiac focus is, its likelihood ratio for trisomy 21, and your management in this woman. (4 marks) (c) The same scan now reports hyperechogenic bowel. How does this change your differential and your work-up? (3 marks) (d) A separate patient has a confirmed major cardiac anomaly with a normal karyotype. State the first-tier genetic test, the expected yield, and the referral pathway. (3 marks)
How this SAQ is marked
Twelve SAQs, 180 marks, two 2-hour papers — roughly 15 marks and 20 minutes each. Marks come from specifics: the ISUOG structures and cardiac views, the likelihood ratio and the prior-screening context, and the platform choice. Write in short labelled points. [1]
Reveal model answer and mark schemeShowHide
(a) Systematic anatomy scan and cardiac views (5 marks)
One mark per structure group and cardiac view, maximum five. [1][2]
- Systematic ISUOG order: head and brain, face, spine, heart, thorax, abdomen, limbs, plus biometry (BPD, HC, AC, FL) and growth.[1]
- Amniotic fluid, placenta, cord and cervix assessed at the same scan.[1]
- Cardiac views: four-chamber, left ventricular outflow tract, right ventricular outflow tract, and three-vessel-trachea.[2]
- A four-chamber view alone is insufficient — it misses transposition and obstructive lesions.[2]
(b) Echogenic intracardiac focus and its management (4 marks)
One mark per point, maximum four. [3][4]
- An echogenic intracardiac focus is a bright spot in the papillary muscle, usually a benign calcification; it is a soft marker for trisomy 21.[4]
- Positive likelihood ratio about 5.8 (Agathokleous 2013); most isolated markers have only a small effect on pre-test odds.[3]
- In this woman (low-risk cfDNA, isolated finding, otherwise normal scan), the appropriate management is reassurance and routine care — not amniocentesis.[4]
- Counsel that the marker is common and does not by itself indicate Down syndrome in a low-risk context.[3]
(c) Hyperechogenic bowel — differential and work-up (3 marks)
One mark per point, maximum three. [1]
- Differential is broader than aneuploidy: chromosome anomaly, cystic fibrosis, congenital infection (CMV), and bowel obstruction or meconium peritonitis.[1]
- Work-up: detailed fetal-medicine review, microarray, maternal CF carrier testing, and congenital-infection screen (CMV serology) as indicated.[1]
- Counselling is proportionate to the finding and the work-up results.[1]
(d) Major cardiac anomaly, normal karyotype — test, yield, pathway (3 marks)
One mark each for test, yield and pathway. [8]
- First-tier test: chromosomal microarray (not repeat karyotype).[8]
- Expected yield: clinically relevant copy-number variants in about 6.0% of structurally abnormal fetuses with a normal karyotype (Wapner 2012).[8]
- Pathway: fetal-medicine referral, detailed fetal echocardiography, and a multidisciplinary plan for place of delivery and neonatal cardiology; clinical genetics for any abnormal result.[2]
References5ShowHide
- [1]Salomon LJ, Alfirevic Z, Berghella V, et al. ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan Ultrasound Obstet Gynecol, 2022.PMID 35592929
- [2]International Society of Ultrasound in Obstetrics and Gynecology, Carvalho JS, Allan LD, et al. ISUOG Practice Guidelines (updated): sonographic screening examination of the fetal heart Ultrasound Obstet Gynecol, 2013.PMID 23460196
- [3]Agathokleous M, Chaveeva P, Poon LC, et al. Meta-analysis of second-trimester markers for trisomy 21 Ultrasound Obstet Gynecol, 2013.PMID 23208748
- [4]Lorente AMR, Moreno-Cid M, Rodríguez MJ, et al. Meta-analysis of validity of echogenic intracardiac foci for calculating the risk of Down syndrome in the second trimester of pregnancy Taiwan J Obstet Gynecol, 2017.PMID 28254219
- [8]Wapner RJ, Martin CL, Levy B, et al. Chromosomal microarray versus karyotyping for prenatal diagnosis N Engl J Med, 2012.PMID 23215555