Had sex one week before my gf'speriod.a normal period arrived on time. does it mean she wont get pregnant and when can we take a blood test(not hpt)?

Got regular periods?: A woman cannot get her normal regular period and be pregnant at the same time. However, she can get pregnant a week or two after her normal period. If she has some spotting or light bleeding that doesn't look like her normal regular period, she can check a urine pregnancy test about 3 weeks after sex (3 weeks after when conception might have happened) to see if she is pregnant.