Differentiating an early intrauterine gestational sac from a "pseudosac" on ultrasound.

Pseudosac refers to fluid or blood in endometrial cavity and is typically associated with ectopic pregnancies.

A true gestational sac is located paracentrically within the decidua and features a distinct, highly echogenic border.

In contrast, a pseudosac sits centrally between decidual layers and lacks this echogenic ring.