1. 1. F. Cunningham, Kenneth Leveno, Steve Bloom, John Hauth, Dwight Rouse, Catherine Spong, eds. William's Obstetrics 23rd ed. New York: McGraw Hill Professional: 2009: 894.
2. Verbesserte Friih diagnose der intrauterinen Schwangerschaft durch Ultraschall - Vaginalsonde;Haid;Geburts Frauenheilk,1985
3. Vaginale Sonographie der intakten Graviditaet im ersten Trimenon;Rempen;Geburtsh Frauenheilk,1987
4. 4. F. Cunningham, Kenneth Leveno, Steve Bloom, John Hauth, Dwight Rouse, Catherine Spong, eds. William's Obstetrics 23rd ed. New York: McGraw Hill Professional: 2009: 891-892.
5. 5. F. Cunningham, Kenneth Leveno, Steve Bloom, John Hauth, Dwight Rouse, Catherine Spong, eds. William's Obstetrics 24rd ed. New York: McGraw Hill Professional: 2014: 39.