Ultrasound is performed during the first trimester of pregnancy, by which an echogenic area in the uterine cavity, often clinically a gestational sac, is detected. It is recommended to analyze it comprehensively with clinical history and days of menopause. In most cases, the gestational sac is visible in the uterus by ultrasound at about 40 days after menopause, and the yolk sac can be seen within the gestational sac. If the menopause has not exceeded 40 days, through the ultrasound examination may see the anechoic area, this situation may be the embryo stops developing, or may be due to the menopause days are relatively short, so the gestational sac is not clear, it is recommended to do another ultrasound examination every 5 days, if normal, you will see a clear gestational sac. If the gestational sac is still not visible, it may be due to poor embryonic development.