If the fetal sac is not seen in the ultrasound at 6 weeks of pregnancy, the following situations are generally considered: First, the usual menstruation is irregular, often early or wrong, then ovulation is also irregular. If you have an ultrasound at 6 weeks of pregnancy and the sac is not visible in the uterine cavity, it means that the fertilized egg has not yet been laid, so don’t be anxious and just wait a few more days for ultrasound review. In the second case, if you usually have a very regular menstruation with a cycle of 28-30 days, and you cannot see the fetal sac during the ultrasound at 6 weeks of pregnancy, you should focus on the bilateral adnexal area to see if there is any sound image similar to the fetal sac in the adnexal area. If a fetal sac-like image is observed in the left or right adnexal area, ectopic pregnancy is highly suspected. The third type of pregnancy is a biochemical pregnancy, that is, a spontaneous abortion with a small amount of vaginal bleeding due to poor early development of the fetal sac, which is judged by clinical symptoms.