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J Clin Ultrasound. 2009 Jun;37(5):249-52. doi: 10.1002/jcu.20563.

"Empty" sac in pregnant women with bleeding: are measurements answering the right question?

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  • 1Department of Radiology, University of California, San Francisco, CA, USA.



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.


Retrospective study of all first-trimester sonograms among women with vaginal bleeding during a 4-year interval.


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).


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.

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