LUI, Kwai-Ying, Yun-Ting LEE, Chun-Hong SO, and Ellen LM YU. “Difference in Serum Human Chorionic Gonadotrophin Levels Measured Using the World Health Organization 3rd Versus 5th International Standard: A Correlation Study With Reference to Management of Pregnancy of Unknown Location”. Hong Kong Journal of Gynaecology, Obstetrics and Midwifery 17, no. 1 (January 1, 2017). Accessed May 2, 2024. https://hkjgom.org/home/article/view/219.