The gestational sac can be seen during an ultrasound examination at around 40 days of pregnancy. Most women have a regular menstrual cycle, usually around 28-30 days, or less than 28 days. With a regular menstrual cycle, the time of ovulation is relatively fixed, in the middle of two menstrual cycles. At around 40 days of pregnancy, the fertilized egg will settle into the uterine cavity and the gestational sac will be visible in the uterine cavity during the ultrasound examination. If a normal gestational sac is not visible in the uterine cavity at this time, it is important to focus on the bilateral adnexal areas to see if there are any abnormal echoes in the adnexal areas bilaterally, and if there are any echoes similar to a gestational sac. If an echo similar to a pregnancy sac is found on the left or right side of the adnexal area, it is important to be vigilant and perform blood tests to rule out ectopic pregnancy in conjunction with clinical tests. For women with irregular menstrual cycles, if the ultrasound reveals no echo of a pregnancy sac in the uterine cavity at about 40 days of pregnancy, do not be anxious and wait for a few more days for a follow-up examination, and when the fertilized egg is laid, the pregnancy sac will be seen in the uterine cavity when you check the ultrasound again.