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Encyclopedia > Gestational sac

The gestational sac is the only available intrauterine structure that can be used to determine if an intrauterine pregnancy (IUP) exists, until the embryo is identified. On ultrasound, it is an anechoic (dark) space surrounded by a hyperchoic (white) rim. It is spherical in shape, and usually located in the upper uterine fundus. The mean gestational sac diameter (MGD) is an effective estimate of gestational age between 5 and 6 weeks, with an accuracy of about +/- 5 days. The yolk sac and embryo should be readily identified when the gestational sac reaches a certain size and the yolk sac is 20 mm in size or the fetal pole is 25 mm in size. The uterus or womb is the major female reproductive organ of most mammals, including humans. ... A pregnant woman near the end of her term Pregnancy is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. ... For other uses, see Embryo (disambiguation). ... Ultrasound is a form of cyclic sound pressure with a frequency greater than the upper limit of human hearing, this limit being approximately 20 kilohertz (20,000 hertz). ... A sphere is a perfectly symmetrical geometrical object. ... The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 5 weeks gestation. ... For other uses, see Embryo (disambiguation). ... The fetal pole is a thickening on the margin of the yolk sac of a fetus during pregnancy. ...

Gestational sacs can be identified via ultrasound and are generally identified by the following 4 characteristics:
1. Spherical or ovoid in shape
2. The "double ring" outline, as identified by a white, echogenic outline
3. Located in the uterine fundus
4. Eccentric in the uterus, or located slightly next to the midline of the uterus.

  Results from FactBites:
1st Trimester Ultrasound Scanning (2358 words)
While a gestational sac is sometimes seen as early as during the 4th week of gestation, it may not be seen until the end of the 5th week, when the serum HCG levels have risen to 1000-1500 mIU.
Gestational sac size may be determined by measuring the largest diameter, or the mean of three diameters.
Between the 11th and end of the 13th week of gestation, the measurement of nuchal translucency is obtained with the fetus in saggital section and a neutral position of the fetal head (neither hyperflexed nor extended, either of which can influence the nuchal translucency thickness).
Basic Imaging > Ultrasound of Early Pregnancy (3599 words)
As the Gestation enlarges, the portion of the chorionic trophoblast destined to form the placenta enlarges and remains in intimate apposition to the underlying decidua (decidua basalis).
The presence of fluid in the canal in ectopic gestation carries the risk of mis-identification as an intrauterine pregnancy, and is referred to as a pseudogestational sac.
Gestational Sac first appears in the substance of the decidua (intradecidual) at 4.5 weeks, and should be seen in virtually all normal 5 week intrauterine pregnancies.
  More results at FactBites »



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