the placenta completely covers the cervical os - Abruptio placentae is premature separation of a normally implanted placenta

- In complete (total) placenta previa, the placenta completely covers the cervical os.

- In partial (incomplete or marginal) placenta previa, the placenta covers only a portion of the cervical os.

- Abruptio placentae is premature separation of a normally implanted placenta. It may be partial or complete, and usually causes abdominal pain, vaginal bleeding, and a boardlike abdomen.