Placenta previa occurs when the placenta is implanted either close to or on top of the womb. There are multiple types of this condition including complete, partial and marginal placenta previa.
- Complete placenta previa is where the placenta completely covers the opening from the womb to the cervix.
- Partial placenta previa where the placenta partially covers the cervical opening.
- Marginal placenta previa refers to a placenta that is located next to, but not covering, the cervical opening.
These conditions are often caused by scar tissues in the upper regions of the uterus that can promote growth of the placenta in the unscarred lower segment of the uterus. This can be a result of prior Cesarean deliveries, prior dilation and curettage procedures or any surgery of the uterine cavity. In some cases, it occurs because the placenta grows larger to compensate for decreased ability to deliver oxygen and/or nutrients, or a need for greater function.