Abstract Archives of the RSNA, 2006
Eric E. Sauerbrei MD, Presenter: Nothing to Disclose
1) Review the US features that establish intrauterine pregnancy and thus "rule out" ectopic pregnancy in low risk women.
2) Review the US landmarks of normal early pregnancy (<10 weeks MA) including clinically useful discriminatory levels.
3) Recognize the US signs that are diagnostic of failed intrauterine pregnancy and those signs that are suggestive.
4) Address the topics of "blighted ovum" and early hydatidiform mole.
Early pregnancy failure implies either failure of embryonic tissue to develop within the chorionic sac, cessation of development of the pre-embryonic tissue or death of the embryo after heart activity has started.
Blighted ovum is a pathological term that refers to an empty gestational sac due to failure of progression of the pre-embryonic tissue to the embryonic stage. Most cases of blighted ovum are due to chromosomal abnormalities (often trisomies 16 and 22) and all blighted ova have paternal and maternal chromosomes.
The most useful ultrasound features to diagnose established early pregnancy failure are an empty gestational sac when the mean sac diameter is greater than the discriminatory level (16mm for endovaginal ultrasound, 25mm for transabdominal ultrasound) and absent embryonic heart activity when the crown-rump length is greater than the discriminatory level (5mm for endovaginal ultrasound, 9mm for transabdominal ultrasound).
There are several observations on endovaginal ultrasound that are highly predictive of subsequent first-trimester failure: empty amniotic sac (with yolk sac visible separately), severe bradycardia (6.5mm inner diameter of yolk sac), enlarged amniotic sac (fluid-filled amniotic sac sonographically visible when CRL <7mm), small gestational sac ((MSD-CRL)<5mm).
Complete hydatidiform mole develops when all 46 chromosomes are derived from the father, usually by monospermic fertilization of an oocyte that lacks a nucleus. There is usually no embryonic development. For complete hydatidiform mole less than 10 weeks’ menstrual age, the ultrasound findings can mimic a “blighted ovum” and thus be indistinguishable.
Early Pregnancy Failure: The Role of Ultrasound. Radiological Society of North America 2006 Scientific Assembly and Annual Meeting, November 26 - December 1, 2006 ,Chicago IL. http://archive.rsna.org/2006/4402472.html