A 28-year-old primigravida at 18 weeks of gestation presents for a detailed anatomy scan. The sonographer evaluates the fetal brain, spine, heart, and kidneys. All of the following are recognized second-trimester sonographic findings in normal fetuses EXCEPT:

Explanation

## Normal Second-Trimester Sonographic Findings and Soft Markers **Key Point:** Mild pyelectasis at 18 weeks is a **soft marker**, not a pathological finding requiring immediate intervention. Many fetuses with mild pyelectasis (4–7 mm) have normal postnatal renal function and no structural abnormality. Serial follow-up is recommended, but immediate intervention is not indicated. ### Soft Markers in Second-Trimester Obstetric Ultrasound | Soft Marker | Prevalence | Significance | Management | |-------------|------------|--------------|-------------| | **Choroid plexus cysts** | 1–2% of normal fetuses | Usually benign; resolve by 24 weeks | Reassurance; follow-up if associated with other markers | | **Echogenic intracardiac focus (EIF)** | 3–4% of normal fetuses | Benign; no cardiac dysfunction | Reassurance; no intervention needed | | **Mild pyelectasis (4–7 mm)** | 1–2% of normal fetuses | Benign variant; may be physiologic | Serial follow-up; postnatal renal ultrasound | | **Echogenic bowel** | 0.5–1% of normal fetuses | Associated with meconium; usually benign | Risk assessment for chromosomal abnormality | | **Short femur** | 1–2% of normal fetuses | Benign variant if isolated | Reassurance; genetic counseling if recurrent | **High-Yield:** The distinction between **soft markers** (benign, require follow-up) and **hard markers** (structural anomalies, require intervention) is critical. Mild pyelectasis is a soft marker; severe pyelectasis (>15 mm) or associated hydronephrosis is a hard marker. **Clinical Pearl:** Mild pyelectasis in the second trimester often resolves spontaneously. Postnatal follow-up with renal ultrasound and voiding cystourethrogram (VCUG) is indicated only if pyelectasis persists or worsens, or if other markers are present. **Warning:** Confusing soft markers with pathological findings leads to unnecessary maternal anxiety and over-investigation. Most soft markers are benign variants and do not require fetal intervention in utero. ### Normal Second-Trimester Findings 1. **Choroid plexus cysts:** Present in 1–2% of normal fetuses; benign; typically involute by 24 weeks. 2. **Stomach bubble:** Should be visible on axial views; absence suggests esophageal or duodenal atresia. 3. **EIF:** Present in 3–4% of normal fetuses; benign; no cardiac dysfunction. 4. **Mild pyelectasis:** 4–7 mm renal pelvis diameter; benign variant; requires postnatal follow-up, not fetal intervention. [cite:Callen Ultrasound in Obstetrics and Gynecology 6e Ch 10]