Different ultrasound machines and different obstetricians have errors in their measurements, and the presumed week of pregnancy will be different, so there will be inconsistencies in the results of the two ultrasounds. The week of pregnancy is usually calculated from the first day of the last menstrual period, and the size of the gestational sac and the length of the head-butt diameter in the ultrasound results are usually projected in the early stages of pregnancy. Different ultrasound machines and different ultrasound doctors may have errors in the measurements, and the projected week of pregnancy may also vary. If menstruation is regular, it can be determined whether the pregnancy is intrauterine after 38 days of menopause, and the fetal heart and buds can be detected after 42 days of menopause. If menstruation is irregular, the obstetrician can calculate the last menstruation to calculate the pregnancy week.