Placenta previa is a condition that may happen during the second or third trimester of pregnancy. It's one of the most common causes of vaginal bleeding during these trimesters. It happens when the placenta implants in the lower part of the uterus. This causes the placenta to block part or all of the opening of the cervix to the vagina (birth canal). It can lead to problems for both the mother and baby. This can include blood loss and premature labor. EVERY PREGNANT WOMEN MUST KNOW ABOUT IT.