The fetal heart is the heartbeat of the fetus. The fetal heart is the earliest developing organ among the organs that develop throughout the body. The gestational week series begins on the first day of the last menstrual period, usually 2 weeks before ovulation or fertilization and 3 weeks before implantation. The full course is about 280 days, or 40 weeks. The size of the fetal bud: 4 weeks: the fertilized egg has just completed implantation, the size is very small, and the state of pregnancy is not visible on ultrasound; 5 weeks: the fertilized egg enters the embryonic stage, the primitive cardiovascular vessels appear, pulsation is visible, the small fetal sac is visible on ultrasound, or the fetal bud is visible; 6 weeks: the fetal head, brain vesicles, frontal organs, respiratory, digestive, nervous and other organs begin to differentiate, the fetal bud and fetal heartbeat are visible on ultrasound; 7 weeks: the embryo has the shape of a human being. The fetal buds and heartbeat can be clearly seen on ultrasound. At 8 weeks, the fetal shape is fixed, and the fetal sac takes up about 1/2 of the uterine cavity, the fetal shape and fetal heart are clearly visible on ultrasound, and the yolk sac is visible. Therefore, theoretically, some pregnant mothers can see the faint fetal heartbeat at about 5 weeks at the earliest, and the fetal heartbeat can be clearly seen at about 7 weeks. However, some pregnant mothers with long menstrual cycles, late ovulation and late implantation will have to wait a little later. How long after pregnancy can you hear the fetal heartbeat. The fetal heartbeat can be heard around the midline below the umbilicus in about 4 months of pregnancy, and the position of the fetal heart will change as the fetus grows and the fetal position varies. The fetal heartbeat is usually at 120-160 beats per minute, which is not too regular. It is much more regular in the late pregnancy, but if the fetal heartbeat is too fast or stops for a long time frequently, you should seek medical attention in time.