If the pregnant woman usually has regular menstruation with a menstrual cycle of about 28 days, usually counting from the first day of the last menstrual period and 35 days or 5 weeks after menopause, a vaginal ultrasound examination can reveal a round or oval-shaped gestational sac with a fuller shape, thick walls with cystic echogenicity and an echogenic zone inside. The gestational sac is very small, occupying less than 1/4 of the uterine cavity, and is the original embryonic disc tissue, which can be located in the fundus, anterior, posterior, upper or middle part of the lateral wall of the uterus. The size of the gestational sac is mostly directly related to the gestational age, which can be measured by abdominal or vaginal ultrasound, and the gestational age can be estimated by the size of the sac. If the gestational sac is not seen on time during pregnancy, it needs to be taken seriously. If a woman has delayed menstruation, the time to see the gestational sac will be delayed, so she can continue to observe and review it regularly; if her menstruation is normal but she does not see the gestational sac at the normal time, she needs to consider the possibility of ectopic pregnancy, which is usually accompanied by abnormal vaginal bleeding and low progesterone, and if the pregnancy is diagnosed as ectopic, it should be terminated in time.