title: "Empty" sac in pregnant women with bleeding: are measurements answering the right question?
abstract: OBJECTIVE
  To assess the percentage of first-trimester pregnancies with bleeding that demonstrate a visible sac but lack an identifiable embryo and have a mean sac diameter (MSD) in the controversial range of 16-20 mm.
  
  
  METHODS
  Retrospective study of all first-trimester sonograms among women with vaginal bleeding during a 4-year interval.
  
  
  RESULTS
  The study cohort consisted of 546 first- trimester sonograms. An embryo was not seen in 132 cases (24%). Of these, the MSD in 69 cases (52%) was <16 mm, between 16 and 19 mm in 20 cases (15%), or >or=20 mm in 39 cases (30%). The percentage of women who were threatening to abort who demonstrated a visible sac but lacked an identifiable embryo and had a MSD in the controversial range of 16-20 mm was 3.7% (20/546).
  
  
  CONCLUSIONS
  We found that of 546 sonograms undertaken in pregnant women with vaginal bleeding in the first trimester, only 20 patients (3.7%) fell in the MSD range of 16-20 mm. Therefore, even among those diagnosticians who adopt the most stringent criterion (MSD = 20 mm), an additional examination would be requested in fewer than 1 in 25 patients.
authors.affiliation: Department of Radiology, University of California, San Francisco, CA, USA.
authors.forename: Seerat
authors.initials: S
authors.lastname: Aziz
authors.forename: Richard C
authors.initials: RC
authors.lastname: Cho
authors.forename: Diana B
authors.initials: DB
authors.lastname: Baker
authors.forename: Chloe
authors.initials: C
authors.lastname: Chhor
authors.forename: Roy A
authors.initials: RA
authors.lastname: Filly
mesh_terms: D000033:Abortion, Threatened / Q000000981:diagnostic imaging*; D004622:Embryo, Mammalian / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular / Q000000981:diagnostic imaging*; D011261:Pregnancy Trimester, First; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods; D014592:Uterine Hemorrhage / Q000000981:diagnostic imaging* / Q000209:etiology