Gestational sac

Source: Wikipedia, the free encyclopedia.
Gestational sac
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 stage6a
Days12
PrecursorHeuser's membrane
Identifiers
Latinsaccus gestationalis, coeloma extraembryonicum, cavitas chorionica
MeSHD058746
TEsac_by_E5.8.0.0.1.0.1 E5.8.0.0.1.0.1
Anatomical terminology]

The gestational sac is the large cavity of

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.

Structure

The gestational sac is

gestational age, due to folding of the trilaminar germ disc, the amniotic sac
expands and occupy the majority of the volume of the gestational, eventually reducing the extraembryonic coelom (the gestational sac or the chorionic cavity) to a thin layer between the parietal somatopleuric and visceral splanchnopleuric layer of extraembryonic mesoderm.

Development

During embryogenesis, the extraembryonic coelom (or chorionic cavity) that constitutes the gestational sac is a portion of the conceptus consisting of a cavity between Heuser's membrane and the trophoblast.

During formation of the primary yolk sac, some of the migrating hypoblast cells differentiate into mesenchymal cells that fill the space between Heuser's membrane and the trophoblast, forming the extraembryonic mesoderm. As development progresses, small lacunae begin to form within the extraembryonic mesoderm which enlarges to become the extraembryonic coelom.

The Heuser's membrane cells (hypoblast cells) that migrated along the inner

extraembryonic mesoderm; this disrupts the extraembryonic reticulum. Soon pockets form in the reticulum, which ultimately coalesce to form the extraembryonic coelom.[1]

The extraembryonic coelom divides the extraembryonic

somatopleuric mesoderm
, which lies adjacent to the cytotrophoblast layer of the embryo.

The chorionic cavity is enclosed by the chorionic plate, which is composed of an inner layer of somatopleuric mesoderm and an outer layer of trophoblast cells.

Clinical significance

Ultrasound

Main article: Obstetric ultrasonography
See also: Echogenicity
gestational age. The blue line is the mean, and the green area delimits the 5th and the 95th percentiles.[2]
A: Gestational sac, B: Crown-rump length of embryo, C: Amniotic sac, D: Yolk sac

The mean sac diameter

gestational age[4] between 5 and 6 weeks, with an accuracy of about +/- 5 days.[5]

The yolk sac and embryo should be readily identifiable when the gestational sac reaches a certain size — a yolk sac should be seen when the gestational sac is 20mm and a fetal pole should be seen when the gestational sac reaches 25mm.

Gestational sacs can be identified via ultrasound and are generally identified by the following four characteristics:

  1. The sac has a round or elliptical shape in longitudinal and transverse views
  2. The sac is surrounded by a white echogenic rim (choriodecidual reaction) [6]
  3. The sac is located in the uterine fundus
  4. The sac is not implanted on the midline, but eccentrically (to one side of the uterine cavity line).

See also

References

  1. ^ "Extraembryonic Mesoderm - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2023-03-19.
  2. fertilization age
    of 0 weeks. This extrapolated part is blurred because of uncertain values.
  3. ^ Gaillard, Frank. "Mean sac diameter | Radiology Reference Article | Radiopaedia.org". Radiopaedia. Retrieved 2 October 2021.
  4. PMID 17189967
    .
  5. ^ "Basic Imaging > Ultrasound of Early Pregnancy". Archived from the original on 2007-08-14. Retrieved 2007-10-13.
  6. PMID 26562242
    . Retrieved 2 October 2021.

External links
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