Which ultrasound criterion is used to diagnose IUGR when estimated fetal weight is between the 10th and 50th percentile?

Explanation

## Diagnosis of IUGR: EFW 10–50th Percentile ### Classification of IUGR **Key Point:** When estimated fetal weight (EFW) is between the 10th and 50th percentile, IUGR is diagnosed based on **abdominal circumference (AC) < 10th percentile** rather than EFW alone. This distinction separates **constitutionally small fetuses** (normal growth velocity, normal AC) from **pathologically growth-restricted fetuses** (declining growth velocity, AC < 10th percentile). ### Diagnostic Criteria by EFW Percentile | EFW Percentile | AC Percentile | UA Doppler | Diagnosis | |---|---|---|---| | **< 10th** | Any | Any | IUGR (confirmed) | | **10–50th** | **< 10th** | Normal or abnormal | IUGR (AC criterion) | | **10–50th** | ≥ 10th | Normal | Constitutionally small (not IUGR) | | **10–50th** | ≥ 10th | Abnormal | Borderline IUGR / at-risk | ### Rationale **High-Yield:** AC reflects liver size and glycogen stores—it is the most sensitive biometric marker for acute placental insufficiency. A normal AC in a small fetus suggests **symmetrical, constitutional smallness** (e.g., genetic, ethnic factors), not pathological IUGR. **Clinical Pearl:** The **AC-to-HC ratio** and **FL-to-AC ratio** are additional tools: - AC/HC < 0.80 → asymmetrical IUGR (placental insufficiency) - AC/HC ≥ 0.80 → symmetrical IUGR (intrinsic fetal factors, infection) ### Doppler Role - **Normal UA Doppler + AC < 10th** → IUGR (likely early-onset, milder) - **Abnormal UA Doppler + AC < 10th** → IUGR (likely late-onset, more severe) - **Normal UA Doppler + AC ≥ 10th** → Constitutionally small, reassuring