Tags: Anatomical Structure, Embryology.
The gestational sac (or gestation 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 sac diameter (MSD) 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—a yolk sac should be seen when gestational sac is 20mm and a fetal pole should be seen when the gestational sac reaches 25mm.
