Final answer:
Placenta previa is characterized by heavy uterine bleeding in the latter half of pregnancy. It occurs when the placenta partially or completely covers the opening of the cervix. This condition is a common cause of antepartum hemorrhage.
Step-by-step explanation:
The classic sign of placenta previa is the sudden onset of heavy uterine bleeding in the latter half of pregnancy. Placenta previa occurs when the placenta partially or completely covers the opening of the cervix as the fetus grows. This condition is the leading cause of antepartum hemorrhage, which is profuse vaginal bleeding after week 24 of pregnancy but prior to childbirth.