The gestational sac is usually not visible on the 26th day of pregnancy, and it is usually visible only on the 35-40th day of menopause, and pregnant women do not need to perform premature obstetrical examinations. The days of pregnancy are usually calculated from the first day of the last menstrual period. 26 days of pregnancy is about 4 weeks of pregnancy and the gestational sac has not yet formed at this stage and is difficult to observe during ultrasonography. The gestational sac can usually be observed after 35 days of pregnancy and can be round or oval, with a diameter of about 1.0-1.5 cm, located at the base, anterior and posterior walls of the uterus, with a relatively clear outline. Whether the gestational sac can be seen or not is related to the ovulation period and the early or late formation of the fertilized egg. If both ovulation and the formation of the fertilized egg are late, the appearance of the sac will be relatively late. In most people, an ultrasound examination is performed at 6-7 weeks of pregnancy, i.e. 35-42 days after conception, and the gestational sac can be seen in the outline of the enlarged uterus, and the germinal bud, fetal heartbeat and yolk sac can also be observed. Pregnancy is usually determined within 40 days of menopause based on early pregnancy reactions such as nausea, vomiting and physical weakness, as well as the examination of HCG indicators. The examination of the gestational sac can be performed around 35-42 days of pregnancy, and if it is still not found, an ultrasound review can also be performed after 1 week. If abnormalities such as vaginal bleeding and abdominal pain occur, promptly go to the hospital for examination.