Gestational sac
Citation, DOI & article data
- Gestational sac (GS)
The gestational sac (GS) is the first sign of early pregnancy on ultrasound and can be seen with endovaginal ultrasound at approximately 3-5 weeks gestation when the mean sac diameter (MSD) would approximately measure 2-3 mm in diameter.
A true gestational sac can be distinguished from a pseudogestational sac by noting:
its normal eccentric location: it is embedded in endometrium, rather than centrally within the uterine cavity
- presence of the double decidual sign (most helpful at 4.0-6.5 weeks)
- presence of a yolk sac: seen at approximately 5.5 weeks (unequivocal evidence of a gestational sac)
However, caution should be exercised with a diagnosis of a pseudogestational sac. In a woman with a positive beta-hCG, any intrauterine sac-like fluid collection seen on ultrasound is highly likely to be a gestational sac 3.
Some suggest that if the beta-hCG level is >1800 mIU/ml (second international standard) a transabdominal ultrasound should be able to identify an intrauterine gestational sac, however, this value is debatable, and beta-hCG levels >2000 (or even >3000) without a visualized intrauterine gestational sac does not rule out an intrauterine pregnancy 4. Treatment for a suspected failed pregnancy should not be initiated on a hemodynamically stable woman on the basis of a single beta-hCG level 5.
If one cannot identify a yolk sac at a mean gestational sac diameter of 16-24 mm, this is suspicious for, though not diagnostic of a failed early pregnancy.
See also
References
- 1. Ralph Weissleder. Primer of Diagnostic Imaging. (2011) ISBN: 0323065384
- 2. Patricia Chudleigh, Basky Thilaganathan. Obstetric Ultrasound: How, Why and When. (2005) ISBN: 0443054711
- 3. Doubilet P. Ultrasound Evaluation of the First Trimester. Radiol Clin North Am. 2014;52(6):1191-9. doi:10.1016/j.rcl.2014.07.004
- 4. Doubilet P & Benson C. Further Evidence Against the Reliability of the Human Chorionic Gonadotropin Discriminatory Level. J Ultrasound Med. 2011;30(12):1637-42. doi:10.7863/jum.2011.30.12.1637
- 5. Doubilet P, Benson C, Bourne T, Blaivas M. Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester. N Engl J Med. 2013;369(15):1443-51. doi:10.1056/nejmra1302417
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