The most accurate way to completely rule out pregnancy is to have a blood test for HCG, which is a protein hormone secreted by the placenta, and it is only on the seventh day after the formation of the fertilized egg that the placenta begins to synthesize the protein hormone, HCG, so the elevation of HCG can only be detected on the eighth day after the formation of the fertilized egg. If the HCG is not elevated and is less than the normal value, it means that there is no pregnancy, and this is the most accurate method. The ultrasound can detect pregnancy, but when the gestational sac has not yet grown large enough to be seen under the ultrasound, it cannot be said that there is no pregnancy, sometimes it can only be said that the gestational sac has not yet grown and cannot be detected by ultrasound, but in fact it is pregnant.