If you usually have regular periods, with periods every thirty days, each time 3-7 days clean, when the ultrasound is done it indicates six weeks of pregnancy, the actual time of conception may be four weeks. Because ovulation occurs fourteen days before the next menstrual period if you have regular periods, which is two weeks, the time of fertilization is two weeks less than the time calculated by the last menstrual period. If you are six weeks pregnant, you should be able to see the gestational sac in the uterine cavity and see the fetal heartbeat on ultrasound. If you plan to have a baby, you should have regular prenatal checkups, take rest and avoid sex. You should start taking folic acid until twelve weeks after pregnancy, eat more green vegetables and fruits, and keep your bowels open. If you find abnormalities such as abdominal pain or vaginal bleeding, you should go to the hospital promptly.