Classification of Placental Separation 5 cm from the Cervix
A placenta located 5 cm from the internal cervical os is classified as neither complete, marginal, nor partial placenta previa—it is a normal placental position. 1
Understanding Placenta Previa Classification
The modern classification system for placental position has evolved significantly, moving away from traditional terminology toward a more clinically relevant distance-based approach:
Current Distance-Based Classification
- Low-lying placenta: Placental edge is within 2 cm of the internal cervical os but not covering it 1, 2
- Placenta previa (complete): Placenta completely overlies the internal cervical os 1, 3
- Normal placental position: Placental edge is ≥2 cm from the internal cervical os 1
Why 5 cm Represents Normal Position
At 5 cm from the internal cervical os, the placenta is well beyond the 2 cm threshold that defines low-lying placenta, making this a normal placental location that requires no special management or follow-up imaging. 1, 2
- Research demonstrates that no patient with a placental edge >2 cm from the internal cervical os required cesarean section for placenta previa 2
- The American College of Radiology explicitly states that if the placenta is ≥2 cm from the internal os at 18-20 weeks, follow-up evaluation is not necessary 1
Clinical Implications of the 2 cm Threshold
The 2 cm cutoff has strong clinical validation:
- Patients with placental edge-to-internal os distance >10 mm (1 cm) can deliver vaginally in more than two-thirds of cases without increased hemorrhage risk 4
- Seven of eight patients with distance ≤2 cm required cesarean section due to bleeding characteristic of placenta previa 2
- The traditional classification system (complete, partial, marginal) has been rendered obsolete by transvaginal ultrasound measurement capabilities 2
Common Pitfall to Avoid
Do not confuse historical terminology with current evidence-based classification. The terms "partial" and "marginal" placenta previa are outdated and have been replaced by the distance-based measurement system that provides more clinically relevant prognostic information. 2, 1
The question's answer options reflect obsolete terminology that does not align with current diagnostic standards, where precise measurement of the placental edge-to-internal os distance guides clinical decision-making rather than categorical labels. 1, 2