Final answer:
Placenta previa is the medical term for the abnormal implantation of the placenta in the uterus covering the cervical internal os. It is the leading cause of antepartum hemorrhage.
Step-by-step explanation:
The medical term for the unusual implantation of the placenta in the uterus covering the cervical internal Os is placenta persia. Placenta previa occur when the embryo implants close to the internal Os of the uterus, and as the fetus grows, the placenta partially or completely covers the opening of the cervix. It is the leading cause of antepartum hemorrhage, which is profuse vaginal bleeding after a week 24 of pregnancy but before childbirth.