Piya-Anant, M., S. Angsuwathana, M. Thamkhantho, K. Paytay, and G. Chiravacharadej. “The Comparative Study of Different Contraceptive Methods between Copper T 380A and Norplant 6 Siriraj Experience”. Siriraj Medical Journal, vol. 59, no. 6, Nov. 2007, pp. 287-9, https://he02.tci-thaijo.org/index.php/sirirajmedj/article/view/246160.