There are three methods to detect pregnancy after intercourse, one is blood HCG test; the other is urine pregnancy test; the third is ultrasonography. 1.Blood HCG starts to rise in 8-10 days after intercourse, and can be detected by blood HCG test after 10 days with high accuracy. 2. The urine pregnancy test is performed by detecting whether the urine contains a certain amount of human chorionic gonadotropin (HCG). The urine pregnancy test is best performed using morning urine because morning urine is concentrated and the hormone level is higher, which reduces the error rate. Urine pregnancy test paper test needs to be checked half a month after intercourse and is affected by many factors and there is a certain error, so the operator needs to use it strictly according to the instructions. 3.Ultrasound examination to see the pregnancy sac to determine pregnancy. If you have regular menstruation, you can see the gestational sac on vaginal ultrasound at about 5 weeks of menopause, about 20 days after intercourse, and the fetal heartbeat at about 6 weeks of menopause (42 days). Abdominal ultrasound is a little later than vaginal ultrasound. If you have had intercourse for more than half a month, you can buy an early pregnancy test to do a preliminary screening and go to the hospital for an ultrasound after you are sure you are pregnant. If your period is delayed for more than a week, you can go to the hospital for a urine test or ultrasound to determine if you are pregnant.