A pregnancy empty sac appears as a fetal bud no later than 50 days after conception. An empty sac in pregnancy is when a woman is pregnant and an ultrasound examination reveals a cystic dark area in the uterine cavity without finding a yolk sac, fetal buds or fetal heart. Usually, the yolk sac can be seen on ultrasound around 42 days of pregnancy, and fetal buds can be found on the 50th day of pregnancy. So if the pregnancy is short, it is normal to find an empty sac. If the pregnancy is more than 50 days old and no fetal buds or fetal heart can be found in the uterine cavity, it can usually be diagnosed as empty sac pregnancy, which is mostly caused by abnormal embryonic development, and its common causes include chromosomal abnormalities, abnormal quality of sperm or egg, viral infections in early pregnancy, environmental factors, immune factors and so on. In addition, because the diagnosed empty sac pregnancy can not continue to develop into a normal embryo, so there is no significance of preserving the fetus, the patient should promptly go to the gynecology department of the hospital for consultation.