The medical term for your period is menstruation. Pregnancy can be detected by blood HCG with three days to go, but it cannot be detected by using test strips or pregnancy tests.
When a woman has intercourse during ovulation, the sperm and egg combine to form a fertilized egg that will settle, and HCG in the body will rise rapidly, so you can test blood HCG or urine HCG to determine if you are pregnant.
Generally speaking, HCG in the blood rises earlier, one week after intercourse, you can draw blood to check blood HCG to determine pregnancy, so there are still three days to menstruation when you can detect pregnancy, the accuracy is higher. The HCG in urine rises slowly, and pregnancy can only be detected after 2 weeks of coitus or when menstruation is delayed for 3 to 7 days.
If you suspect that you are pregnant, you need to closely observe your menstrual cycle, and once your period is delayed, you should check your blood HCG or use a test strip to see if you are pregnant.