If the pregnancy is still only 20 days old, an ultrasound will not show it at this stage. The days of pregnancy are counted from the first day of menstruation, not from the time of intercourse. If you are 20 days pregnant from the first day of menstruation, you will not be able to see it on ultrasound. If the patient is counting from the time of intercourse, by this stage, the menopause will have been more than 30 days, and at this time, the ultrasound may be able to see the pregnancy sac in the uterine cavity. The purpose of ultrasound is to determine the location and size of the gestational sac and to rule out ectopic pregnancy. ultrasound is a common test during pregnancy, and it is recommended that it be done around 40 days after menopause.