With the yolk sac there is a higher chance of fetal heartbeat, and you need to follow the doctor’s instructions to review the test on time. During early pregnancy, ultrasound should be performed under the supervision of a doctor to identify the intrauterine pregnancy, and also to find out how the embryo is developing. The yolk sac is a small round sac-like structure next to the embryonic bud. Generally, when the yolk sac is seen on ultrasound, and the yolk sac is clear and of normal size, it can indicate that the embryo is well developed, and the chances of fetal heartbeat are also relatively high, and it can be rechecked around 6 weeks of pregnancy according to the doctor’s instructions. Generally, the yolk sac can be seen in the vaginal ultrasound examination at 5 weeks of pregnancy, the diameter of the normal range of 0.3 ~ 0.8 cm, the average is 0.5 cm. When the yolk sac > 1.0 cm or < 0.3 cm, deformation, internal strong echogenicity and other abnormalities, it is mostly suggestive of underdevelopment of the embryo, but also with the combination of progesterone and blood levels of HCG (human chorionic gonadotropin), when necessary, carry out birth control treatment, and on time! Review on a regular basis.