A pseudogestational sac, also known as a pseudosac or intra-cavitary fluid, is the concept that a small amount of intrauterine fluid in the setting of a positive pregnancy test and abdominal pain could be erroneously interpreted as a true gestational sac in ectopic pregnancy.

The sign was originally reported before the use of transvaginal ultrasound imaging and caution should be exercised if considering diagnosing a pseudogestational sac with modern ultrasound equipment. 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 ⁶.

Radiographic features

Ultrasound

generally irregularly-shaped with pointed edges and/or filled with debris, sometimes referred to as 'beaking'
centrally located in the endometrial cavity, rather than eccentrically located within the endometrium
displaces the anterior and posterior endometrial cavity surfaces
does not demonstrate a yolk sac
a double decidual layer is compatible with intrauterine pregnancy, but lack of this sign is not specific for pseudogestational sac
- may be surrounded by a thick decidual layer

It should be distinguished from an intradecidual sign, which is also a sign of early pregnancy.

The idea of beta-hCG "discriminatory levels" has also fallen out of favor since this sign was formulated. Caution should be exercised in making a diagnosis of pseudogestational sac based on a beta-HCG level at which a yolk sac is expected to be seen as this has been shown to be unreliable. Therapy should not be initiated in a haemodynamically-stable woman on the basis of a single beta-hCG level.