Which of the following is the most common type of placenta previa encountered clinically?

Explanation

## Classification of Placenta Previa Placenta previa is classified based on the relationship of the placental edge to the internal cervical os: | Type | Definition | Frequency | |------|-----------|----------| | **Low-lying** | Placenta is in lower uterine segment but does not reach the os | ~50–60% | | **Marginal** | Placental edge reaches the internal os margin | ~25–30% | | **Partial** | Placenta partially covers the internal os | ~10–15% | | **Complete** | Placenta completely covers the internal os | ~5–10% | **Key Point:** Low-lying placenta is the most common type encountered clinically, accounting for approximately 50–60% of all cases of placenta previa (broadly defined). This is consistent with data from Williams Obstetrics and Dutta's Textbook of Obstetrics, which note that the majority of cases diagnosed on ultrasound — particularly in the second trimester — represent low-lying placenta, most of which resolve by term due to "placental migration" (differential growth of the lower uterine segment). **Clinical Pearl:** The term "placental migration" refers to the apparent movement of the placenta away from the internal os as pregnancy advances and the lower uterine segment develops. Up to 90% of cases of low-lying placenta diagnosed before 20 weeks resolve by term, making it the most commonly encountered — and most commonly resolving — type in clinical practice. **High-Yield:** Among the types that persist to term, complete placenta previa carries the highest risk of antepartum hemorrhage and mandates cesarean delivery. Low-lying placenta, being the most common type, is also the most likely to be encountered on routine anomaly scans and requires follow-up ultrasound at 32–36 weeks to confirm resolution. *(Reference: Dutta DC, Textbook of Obstetrics, 9th ed.; Williams Obstetrics, 25th ed.)*