Traditionally, placenta previa has been categorized into 4 types (1):
1. Complete placenta previa: where the placenta completely covers the internal os;
2. Partial placenta previa: where the placenta partially covers the internal os. Thus, this scenario occurs only when the internal os is dilated to some degree;
3. Marginal placenta previa: where placenta just reaches the internal os, but does not cover it;
4. Low-lying placenta: where placenta extends into the lower uterine segment but does not reach the internal os.