PURPOSE: To compare gestational sac (GS) volume (GSV) between normal pregnancies and missed abortions and anembryonic pregnancies and to determine at what gestational age differences in GS volume become evident. METHODS.: GSV in missed abortion and anembryonic pregnancy were measured using three-dimensional ultrasound and the results were compared with GSV in normal pregnancies. Pregnancies between 6 and 12(+6) gestational weeks of age according to last menstrual period were included in normal pregnancies, missed abortions, and anembryonic pregnancies. RESULTS: There were 141 normal pregnancies and 82 missed or anembryonic abortions. GSV was significantly larger in normal pregnancies than in missed or anembryonic abortion: 27.51 + or - 25.25 cm(3) and 8.04 + or - 10.54 cm(3), respectively (p < 0.001). When stratified by weeks, statistically significant differences were found beginning at 7 weeks, while GSV measurements were not significantly different between the normal and abnormal pregnancies from 6 to 6(+6) weeks. CONCLUSION: GSV in missed abortion and anembryonic pregnancies is significantly smaller than in normal pregnancies, starting at 7 weeks of gestational age. This finding may be helpful in the diagnosis of missed abortion or anembryonic pregnancies in selected cases.
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