A 36-day pregnancy ultrasound can usually see the gestational sac, but there are individual variations. Vaginal ultrasound is a type of ultrasound that is performed by placing a probe inside a woman’s vagina. The probe is placed close to the uterus and its attachments, so the image looks clear and high resolution, and the gestational sac can be seen earlier. Due to the thickness of abdominal fat, you may not be able to see the gestational sac on the 36th day of pregnancy, and you need to wait for another week for review. However, if you have irregular periods, late ovulation, delayed implantation of the fertilized egg, and slower growth and development of the embryo, you may not see the gestational sac on the 36th day of pregnancy. If you can’t see the gestational sac on the 36th day of pregnancy, don’t worry too much, you can check the blood HCG for early pregnancy identification, and then wait for a week to go to the hospital for ultrasound examination to make it clear.