The yolk sac is a normal sac-like structure formed by the inward lamellar cleavage of the trophectoderm of the cell. The normal development of the embryo depends on the production of the yolk sac, which disappears naturally after 12 weeks of development. Usually, the fetal bud can be seen 7-8 days after the yolk sac is seen, and the fetal heart can be seen after another week or so. If a pregnant woman usually has regular menstrual periods of 28-30 days, at 35 days of menopause, the gestational sac and yolk sac can be seen in the uterine cavity by ultrasound, marking intrauterine conception. The gestational sac can usually be seen more clearly around 6 weeks of pregnancy and will gradually disappear at 10-12 weeks of pregnancy. Usually after 6-7 weeks of pregnancy, the fetal bud and primitive heart tube beat can be seen on ultrasound. The rhythmic beating of the fetal heart can be seen in the fetal bud, which is an important early sign of embryo survival. If a pregnant woman has irregular menstrual periods before pregnancy, ovulation may be delayed and the formation of the fetal heart and fetal buds may be delayed, usually the fetal heart and fetal buds can be seen around 60 days of pregnancy. If no fetal bud is observed after 10-14 days of yolk sac appearance, it may be embryonic abortion, continue to observe for another 1 week, if you still cannot see fetal heart and fetal bud, you can basically diagnose embryonic abortion, combined with progesterone and HCG test, you can clearly diagnose whether embryonic abortion; if fetal bud appears more than 5-7mm, but fetal heart still does not appear, you can also be diagnosed as embryonic abortion, at this time, you should give timely termination of the pregnancy by removing the uterus. If the fetal germ is more than 5-7mm and the fetal heart is still not present, then timely termination of pregnancy should be performed.