Rugpao, S., K. Amatayakul, Y. Yutabootr, S. Suwankiti, A. Sontirat, and S. Sethasathien. “Vaginal Bleeding Patterns Among Lactating Women Using Contraceptive Methods”. Thai Journal of Obstetrics and Gynaecology, vol. 4, no. 1, Jan. 1992, pp. 33-41, https://he02.tci-thaijo.org/index.php/tjog/article/view/257853.