page_title: Gestational sac
hierarchical_section_title: Gestational sac
caption_attribution_description: English: Obstetric ultrasound of embryo at 5 weeks, measuring 3 mm, with yolk sac above.
context_page_description: 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 is identified.
  On obstetric ultrasound, the gestational sac is a dark space surrounded by a white rim.
context_section_description: 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 is identified.
  On obstetric ultrasound, the gestational sac is a dark ("anechoic") space surrounded by a white ("hyperechoic") rim.
caption: Contents in the cavity of the uterus seen at approximately 5 weeks of gestational age by obstetric ultrasonography.
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