The presence and absence of the yolk sac may be an abnormality of embryonic development. Yolk sac is the embryogenesis after the body fold, the proto-gut is obviously divided into intra-embryonic proto-gut and extra-embryonic yolk sac, which contains more yolk, and the wall of the yolk sac has extra-embryonic endoderm and extra-embryonic mesoderm formation. The yolk sac usually appears between 5-7 weeks of pregnancy. If the yolk sac was found in the previous examination but not in the recent examination, the pregnant woman needs to be alerted to the fact that there is an abnormal development of the embryo. Usually at this time, the pregnant woman needs to further combine with other test results such as progesterone and blood HCG values to comprehensively determine the condition. If the test found that progesterone, blood HCG value decreased, and the pregnant woman recently had vaginal bleeding, abdominal pain and other uncomfortable symptoms, it is considered to be due to miscarriage. If the progesterone and HCG values rise slowly or not at all, the embryo is considered to be underdeveloped or undeveloped. During pregnancy, pay attention to rest more, at the same time should relax, avoid tension, anxiety, any discomfort should be timely to the hospital, by the doctor to clarify the diagnosis, and cooperate with the doctor to deal with the symptoms.