What is a gestational sac? The gestational sac refers to a pouch formed in the female uterus to store the embryo. The gestational sac is a sign of early pregnancy. The presence of the gestational sac can usually be detected in the uterus 2-4 days after conception. How to measure the size of the gestational sac. The size of the gestational sac is an important indicator for evaluating whether the pregnancy is developing normally and whether there is threatened abortion. The size of the gestational sac is generally measured through ultrasound examination. The specific measurement method is as follows: 1. Let the woman lie on the examination bed and insert the vaginal probe into the vagina; 2. Place the probe close to the endometrium and adjust the ultrasound