The gestational sac may or may not be visible at 35 days of pregnancy. The time to calculate pregnancy starts from the first day of the last menstrual period. If the pregnant woman has regular menstrual cycles and keeps them at 28-30 days, the gestational sac can usually be seen by vaginal ultrasound at 35 days of pregnancy. If the menstrual cycle is irregular or there is a delay in ovulation, you may not be able to see the gestational sac and it is recommended to repeat the examination after 1 week. After seeing the gestational sac, it is important to observe whether there is a yolk sac inside. If the yolk sac can be seen, it can be clearly identified as a live intrauterine fetus. If it is the first pregnancy and there are no special circumstances, it is not necessary to do an ultrasound at 35 days of pregnancy. You can wait until about 42 days of pregnancy to do a pelvic 3D ultrasound, when most of the fetal heartbeat can be seen in the uterine cavity. However, if you have symptoms such as abdominal pain or vaginal bleeding on day 35 of pregnancy, it is recommended to have an ultrasound examination and a blood test for HCG, progesterone and estradiol levels, which can indirectly determine the quality of the embryo. If HCG is already significantly elevated on day 35 of pregnancy, above 2000 IU/mL, the gestational sac should be visible in the uterine cavity. If there is no gestational sac in the uterine cavity, it is important to note that it may be an ectopic pregnancy, which manifests as abdominal pain and vaginal bleeding after menopause and may pose a risk to the life of the pregnant woman, so it is important to pay attention to the screening.