Placenta previa happens when the placenta moves into the lower part of the uterus and the covers the cervix. Vaginal bleeding often occurs alongside placenta previa. There should not be any vaginal or abdominal pain. You are at a greater risk for placenta previa if you are carrying multiples, have already had a baby, or have underwent a C-section beforehand.
Placenta abruption happens when the placenta detaches from the uterus wall. This is dangerous because the placenta is how your baby receives oxygen and food. This is more likely to occur later in pregnancy and may include stomach aches and vaginal bleeding. High risk women for placenta abruption include being over the age of 35, having sickle cell anaemia, or if you have had children previously.