The ultrasound sheet will describe the size of the gestational sac by three values, such as 15mm x 8mm x 9mm, 15mm for the length, 8mm for the width, and 9mm for the thickness, when the three data of the gestational sac are tested. represents the width and 9mm represents the thickness. The size of the gestational sac is measured by ultrasound to estimate the gestational age of the fetus and to determine the growth and development of the embryo. The formula for calculating the number of days of pregnancy is to add up the three values ÷ 3 + 25, for example, if the above example is 15mm x 8mm x 9m, the number of days of pregnancy is (15 + 8 + 9) ÷ 3 + 25, which is around 35 days. It should be noted that when measuring the size of the gestational sac with ultrasound, sometimes there is an error, if the error is within 0.5cm, it can be considered normal, if it is more than 0.5cm, it is necessary to make a judgment in combination with other indicators of the fetus to assess the growth and development of the embryo. Therefore, you cannot make a judgment about the growth and development of the gestational sac based on the size of the gestational sac alone. In addition, besides the size of the gestational sac, it is also necessary to see if the structure of the gestational sac is normal.