The gestational sac can be seen by ultrasound at the earliest around 5 weeks after pregnancy, and about 3-4 days earlier with a negative ultrasound, if you want to see it earlier. However, the current medical opinion is that if you want to have a baby, it is not recommended to use ultrasound in the early stage. To be on the safe side, it is recommended to wait until about 7 weeks for an abdominal ultrasound to see if the gestational sac is inside or outside the uterus and if there is a fetal heart, fetal bud and yolk sac. If the fetal heart, fetal bud and yolk sac can be seen in the uterus, it proves that the pregnancy is intrauterine and the fetus is good, so you can continue to observe until about 12 weeks of pregnancy to do an ultrasound to see the thickness of the nuchal translucency layer of the fetus.