Generally speaking, the pregnancy sac can be seen by ultrasound in about 5 to 6 weeks from the first day of the last menstrual period, but due to individual differences, some pregnant women can see the pregnancy sac relatively late by ultrasound. After pregnancy, the development of the embryo has a certain pattern, usually around the 5th to 6th week of pregnancy, the gestational sac can be seen through ultrasound at this time. However, some pregnant women have irregular menstruation or long menstrual cycles, which delay the formation of the fertilized egg and the embryo’s implantation, so the gestational sac can only be seen on ultrasound after 5 to 6 weeks. After finding out that you are pregnant, you should go to the hospital for regular checkups. If you can’t see the gestational sac on ultrasound after 5 to 6 weeks, you should cooperate with your doctor to rule out ectopic pregnancy or biochemical pregnancy.