Pregnancy is not diagnosed by the presence or absence of bleeding from implantation. If you want to test for pregnancy, you can use an early pregnancy test for 7 days or more after your period is delayed. If two red lines appear, it usually means positive, which means pregnancy; you can also take a blood test for human chorionic gonadotropin, or HCG, to confirm whether you are pregnant. A blood test for HCG is the earliest and most accurate way to find out if you are pregnant, and can be done 8-10 days after intercourse. Also, an ultrasound can be done over 40 days after menopause to see if there is a fetal sac in the uterus to determine intrauterine pregnancy or a mass in the adnexal area to determine if the pregnancy is ectopic. The bleeding from implantation only occurs in a small number of women and is due to the invasion of the blood vessels of the endometrium while the fertilized egg is implanted in the endometrium, thus causing a small amount of bleeding, which does not occur in everyone, therefore, bleeding from implantation is not used as a diagnostic criterion for pregnancy.