Gestational sac

Gestational sac
Contents in the cavity of the uterus seen at approximately 5 weeks of gestational age by obstetric ultrasonography.
Artificially colored, showing gestational sac, yolk sac and embryo (measuring 3 mm as the distance between the + signs).
Details
Carnegie stage	6a
Days	12
Precursor	Heuser's membrane
Identifiers
Latin	saccus gestationalis, coeloma extraembryonicum, cavitas chorionica
MeSH	D058746
TE	sac_by_E5.8.0.0.1.0.1 E5.8.0.0.1.0.1
Anatomical terminology [edit on Wikidata]

The gestational sac is the large cavity of fluid surrounding the embryo. During early embryogenesis, it consists of the extraembryonic coelom, also called the chorionic cavity. The gestational sac is normally contained within the uterus. It is the only available structure that can be used to determine if an intrauterine pregnancy exists until the embryo can be identified.

On obstetric ultrasound, the gestational sac is a dark (anechoic) space surrounded by a white (hyperechoic) rim.