Antenatal ultrasound at 20 weeks gestation reveals bilateral moderate pyelectasis (renal pelvis AP diameter 7 mm each), echogenic foci in the cardiac ventricles, and a short femur. These sonographic markers are used to calculate which risk assessment?
- A Risk of pre-eclampsia using uterine artery Doppler
- B Individual probability of Down syndrome (Trisomy 21) using the Genetic Sonogram score ✓
- C Fetal growth restriction using biometric ratios
- D Neural tube defect risk using nuchal fold measurement
Explanation
The second-trimester genetic sonogram evaluates soft markers associated with chromosomal anomalies, particularly Trisomy 21. Major soft markers include echogenic intracardiac foci (EIF), pyelectasis, short femur, nuchal fold thickening (most significant), echogenic bowel, and choroid plexus cysts. Each marker modifies the background risk using likelihood ratios to produce an adjusted probability for Trisomy 21. The combination of bilateral pyelectasis, EIF, and short femur in the same fetus substantially increases the Down syndrome probability. Nuchal translucency is a first-trimester marker, distinct from the second-trimester nuchal fold.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.