The best time to check the fetal heartbeat by ultrasound in pregnancy is 7-8 weeks of gestation, but there are individual variations. Clinical gestational weeks are counted from the first day of the last menstrual period. For pregnant women with a normal menstrual cycle of about 28 days, the fetal heart usually appears at 7-8 weeks of gestation, i.e. around 50 days of pregnancy. Some fetuses develop faster in the early stages, and with advanced ultrasound technology, the fetal heartbeat can appear earlier than 7 weeks of pregnancy, and can be detected as early as 6 weeks of pregnancy by transvaginal obstetric ultrasound. If the fetal heart appears too late, the risk of poor fetal outcome is increased. If the fetal heart appears later than 8 weeks of pregnancy, the mother should assess the risk of fetal dysplasia, delayed development, or even arrested development through ultrasound, HCG, progesterone, coagulation, and immune markers, and intervene as early as possible.