aetiology
Last reviewed 01/2018
Placenta praevia may be the result of low implantation of the blastocyst or fusion of the decidua capsularis with the decidua vera. After low implantation placenta praevia is not inevitable, and ultrasound examination has shown the majority of such cases to either abort or resolve as the uterus grows.
A large placenta can causes placenta praevia as its lower portion completely or partially overlaps the internal os.
Atrophy and inflammation, perhaps secondary to previous caesarian section, causes defective decidual vascularisation and hence placenta praevia.