have u googled it? i had a grade 4 previa and the day before i had DS they discovered i also had vasa previa. vasa previa is just where one of the blood vessels from the baby usually runs thru the middle of the placenta, but with previa it sits just over the cervix meaning that if u bleed, it is more then likely the baby's blood. i think with cord insertion, its where the umbilical cord is not in the centre.