Yolk sac is not seen until 8 weeks of pregnancy may be normal or abnormal, need to be analyzed specifically. In normal menstruation women, the cycle is 28-30 days, 35 days after menopause, the ultrasound can see the round or oval gestational sac in the uterine cavity, 6 weeks after menopause, you can see the embryonic buds and the primitive cardiac tube pulsation, therefore, if the menstruation is regular women, the yolk sac can be seen at 8 weeks after conception is abnormal, and we need to consider the development of the embryo is abnormal. If the menstrual cycle is irregular, the cycle 30-90 or even longer, the yolk sac can not be seen at 8 weeks of pregnancy is possible, need to combine with blood HCG, dynamic review ultrasound, to determine the development of the embryo. The yolk sac is an important structure within the gestational sac in early pregnancy, and when ultrasound is performed in early pregnancy, the gestational sac can be seen first, and then the yolk sac can be seen. Next, fetal buds and fetal heart appear, which is a normal process of growth and development of the gestational sac. Pregnant women should have regular checkups and seek prompt medical attention to deal with any abnormalities.