Placenta previa is when the placenta, which carries oxygen and nutrients from the mother’s blood to the baby, has implanted at the bottom of the uterus, partially or completely covering the cervix. For women with placenta previa, the baby cannot be born vaginally due to the placenta blocking access to the birth canal. It is thought that around 1 in every 200 pregnancies is affected and possible causes include scarring of the uterine wall and placenta abnormalities.
For more information;
Better Health Channel – Placenta previa
Mayo Clinic – Placenta previa
Healthdirect – Placenta previa
Source: (Health Direct)