Urogenital Imaging

Blighted ovum

or anembryonic gestation, refers to an ovum which has implanted but in which no embryo has developed. A blighted ovum is destined for failure, and will not lead to successful pregnancy. Blighted ova are common in first trimester abortions, and often demonstrate chromosomal anomalies. Approximately 45% of first-trimester failed pregnancies are due to anembryonic gestation.

The condition is diagnosed on ultrasound (US), based on finding a large gestational sac which does not contain an embryo. Established criteria for the diagnosis of anembryonic gestation for transabdominal US are failure to identify an embryo in a gestational sac with a mean sac diameter of 20 mm or more. Criteria for the diagnosis by transvaginal US are less well established. Conservative criteria would be failure to identify an embryo in a gestational sac with a mean sac diameter of 18 mm or more, or failure to identify a yolk sac in a gestational sac with a mean sac diameter of 13 mm or more. Additional sonographic findings which may be seen in association with an empty sac include irregularity of sac outline, incomplete or absent decidual reaction, absent double decidual sac sign, or presence of a fluid fluid level within the sac.

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