Calculated from the first day of the last menstrual period, 20 days of pregnancy when the fertilized egg has just been laid and has not yet formed a gestational sac, which cannot be seen on ultrasound.Ultrasound is mainly used to check whether there is a gestational sac in the uterine cavity, and the presence of an intact gestational sac means that the woman has succeeded in conceiving. However, the so-called 20 days of pregnancy, if counted from the time of coitus, is about 5 weeks of pregnancy, at this time it is possible to see the pregnancy sac under the vaginal ultrasound, if it is the abdominal ultrasound, may have to wait for another week to see. If the pregnancy sac is still not visible during the ultrasound examination at 6 weeks of pregnancy, it is recommended that the ultrasound examination be repeated 7 days later, and the sac can usually be seen. If there is a delay in detecting the gestational sac in the uterine cavity, ectopic pregnancy needs to be ruled out. Early pregnancy should pay attention to avoid sexual life, do not use drugs without authorization, to stay away from tobacco and alcohol, avoid exposure to radiation. In order to make the fetus in the body can grow smoothly, pregnant women should try to arrange the daily diet life, and must develop a balanced and reasonable diet.