The gestational sac can usually be seen on ultrasound after 35 days of pregnancy, and no later than 42 days of pregnancy. The gestational sac, also known as the gestational sac, is an important indicator for early determination of pregnancy and intrauterine pregnancy by ultrasound. The gestational sac can usually be seen on ultrasound after 35 days of pregnancy and should normally be located in the uterine cavity. The gestational sac is round or oval in shape and has a relatively regular shape and thick walls. At around 42-49 days, the gestational sac can usually be seen to have a developing gestational bud and regular heart tube pulsations. If the gestational sac is not visible after 42 days of pregnancy, or if there is no gestational bud development or cardiac pulsation in the sac after 49 days, or if the shape of the gestational sac is irregular, then abnormal development is most often considered.