1. Rui P, Kang K, Ashman JJ. National Hospital Ambulatory Medical Care Survey: 2016 emergency department summary tables. Available at: https://www.cdc.gov/nchs/data/ahcd/nhamcs_emergency/2016_ed_web_tables.pdf. Accessed January 16, 2021.
2. Sonography in first trimester bleeding;Dighe;J Clin Ultrasound,2008
3. Patterns and predictors of vaginal bleeding in the first trimester of pregnancy;Hasan;Ann Epidemiol,2010
4. AIUM-ACR-ACOG-SMFM-SRU practice parameter for the performance of standard diagnostic obstetric ultrasound examinations,2018
5. Transvaginal sonography in the evaluation of normal early pregnancy: correlation with hCG level;Bree;AJR Am J Roentgenol,1989