Parijchatt, A., and P. Tongswatwong. “Risk Factors Associated with Placenta Previa at Maharat Nakorn Ratchasima Hospital”. Thai Journal of Obstetrics and Gynaecology, vol. 17, no. 4, May 2012, pp. 212-8, https://he02.tci-thaijo.org/index.php/tjog/article/view/1488.