1. International recommendations and guidelines for the safe use of diagnostic ultrasound in medicine
2. American Institute of Ultrasound in Medicine.Recommended Maximum Scanning Times for Displayed Thermal Index (TI) Values.http://www.aium.org/officialStatements/65. Accessed August 28 2022.
3. AIUM Practice Parameter for the Performance of Detailed Second‐ and Third‐Trimester Diagnostic Obstetric Ultrasound Examinations
4. HIllMA.Embryology Carnegie Stage 23.https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_23. Accessed August 28 2022.