A 32-year-old multigravida at 20 weeks of gestation undergoes a detailed morphology ultrasound scan. The sonographer notes a soft marker on fetal anatomy. Which is the most common soft marker detected on second-trimester ultrasound in routine antenatal screening?

Explanation

## Most Common Soft Marker on Second-Trimester Ultrasound **Key Point:** Echogenic intracardiac focus (EIF) is the most frequently encountered soft marker on routine second-trimester morphology ultrasound, present in 3–4% of normal pregnancies. ### Prevalence of Soft Markers on Second-Trimester Ultrasound | Soft Marker | Prevalence (%) | Association with Aneuploidy | Clinical Significance | |-------------|----------------|-----------------------------|-----------------------| | Echogenic intracardiac focus (EIF) | 3–4 | Weak (mainly T21) | Usually benign; resolves by 3rd trimester | | Choroid plexus cyst | 1–2 | Weak (mainly T18) | Usually benign; resolves by 24 weeks | | Pyelectasis | 1–2 | Weak (mainly T21) | May persist; requires postnatal follow-up | | Short femur | 0.5–1 | Moderate (T21, T18) | Requires careful measurement and dating | **High-Yield:** Soft markers are **not diagnostic** of chromosomal abnormality. They are minor anatomical variations that may be associated with aneuploidy but are present in many normal pregnancies. Their detection should **not** trigger immediate invasive testing without additional risk factors. ### Echogenic Intracardiac Focus (EIF) **Definition:** A small echogenic (bright) spot within the fetal ventricle, usually in the left ventricle, thought to represent calcification in the papillary muscle or chordae tendinae. **Epidemiology:** - Present in 3–4% of normal second-trimester fetuses - More common in fetuses of Asian and African ancestry (up to 7–8%) - Usually solitary; multiple foci are rare **Association with Aneuploidy:** - Weak association with Down syndrome (Trisomy 21) - Isolated EIF in a euploid pregnancy has **excellent prognosis** - Risk of aneuploidy increases only if EIF is combined with other markers or abnormal first-trimester screening **Natural History:** - Typically resolves by the third trimester (80% by 32 weeks) - No functional cardiac consequence - No postnatal follow-up required if isolated **Clinical Pearl:** An isolated EIF in a low-risk pregnancy (normal first-trimester screening, normal maternal age) requires **reassurance only**. Invasive testing is not indicated unless combined with other markers or abnormal screening results. ### Comparison with Other Soft Markers **Choroid Plexus Cyst:** - Prevalence: 1–2% - Stronger association with Trisomy 18 (Edwards syndrome) - Usually resolves by 24 weeks - Requires careful assessment of other markers **Pyelectasis:** - Prevalence: 1–2% - Defined as renal pelvis diameter >7 mm at 18–24 weeks - Weak association with Down syndrome - May persist and require postnatal renal ultrasound **Short Femur:** - Prevalence: 0.5–1% - Moderate association with chromosomal abnormalities - Requires accurate dating and comparison with other biometric parameters - Less common than EIF **Mnemonic:** **EIF is EASY** — **E**chogenic **I**ntracardiac **F**ocus is the most **EASY** (common) soft marker to find; **A**ssociation is weak; **S**hould not **Y**ield to invasive testing if isolated. **Warning:** Do not over-interpret soft markers. A single isolated soft marker in a low-risk pregnancy does not warrant amniocentesis or cordocentesis. Counseling should emphasize the benign nature and high resolution rate. [cite:RCOG Green-top Guideline 67; ACOG Practice Bulletin 226]