Threatened abortion: sonographic distinction of normal and abnormal gestation sacs.

In an attempt to determine whether sonographic evaluation alone can distinguish normal from abnormal gestation sacs, a retrospective analysis was performed of ultrasound (US) scans from 168 women with threatened abortion. Gestation sacs were judged to be abnormal on the basis of specific sonographic criteria including large size (greater than or equal to 25 mm mean sac diameter) without an embryo; distorted shape; thin (less than or equal to 2 mm), weakly echogenic, or irregular choriodecidual reaction; absence of a double decidual sac; and low position. Two criteria - large sac and distorted shape - had 100% specificity and were called major criteria. The remaining criteria were individually less specific, although 100% specificity was achieved when three or more of these minor criteria were demonstrated. When one major or three minor criteria were present, 53% of abnormal gestations were correctly identified without any false-positive diagnoses. The authors conclude that experienced sonographers can reliably identify many abnormal gestation sacs on a single examination.