Tannirandorn, Yuen. “Transvaginal Ultrasound in Obstetric Practice”. Thai Journal of Obstetrics and Gynaecology 2, no. 2 (July 1, 1990): 117–133. accessed September 28, 2026. https://he02.tci-thaijo.org/index.php/tjog/article/view/257892.