Jetsawangsri, T., N. Saropala, A. Chittachareon, R. Rangsiprakarn, and Y. Herabutya. “A Preliminary Report on Mid-trimester Routine Ultrasonographic Screening in Ramathibodi Hospital”. Thai Journal of Obstetrics and Gynaecology, vol. 8, no. 4, Dec. 1996, pp. 301-5, https://he02.tci-thaijo.org/index.php/tjog/article/view/92544.