Ultrasound can be done in more than 1 month of pregnancy. If the menstrual cycle is short and ovulation is early, ultrasound can see the gestational sac around 35 days of pregnancy, the fetal bud around 42 days of menopause and the fetal heart around 50 days of menopause. If you do not see the gestational sac or fetal bud after menopause, it is because of the usual irregularity of menstruation or frequent delay of menstruation, late formation of the fertilized egg and late implantation, so you cannot detect the gestational sac, the fetal heart and the fetal bud by ultrasound, so you need to delay for a period of time, and you can see the fetal heart and fetal bud around 50 days. If they are not seen again, there is a risk of ectopic pregnancy or poor development of the gestational sac, signs of miscarriage, or biochemical pregnancy.