21-year-old G3P0 female patient presents to the emergency room at 8 weeks' gestation with vaginal bleeding...

A 21-year-old G3P0 female patient presents to the emergency room at 8 weeks' gestation with vaginal bleeding. History reveals she does not believe she has passed any products of conception. Physical examination reveals there is blood in the vaginal vault and a dilated cervical os. Ultrasound confirms an intrauterine pregnancy and fetal heart motion is observed. The most likely diagnosis is

1. complete abortion
2. incomplete abortion
3. inevitable abortion
4. missed abortion
5. threatened abortion

credit: picmonic.com