The first is that the time of conception is relatively short, and the second is that ovulation test paper can not be used to detect whether a woman is pregnant or not. The sperm and the egg meet to form a fertilized egg after intercourse, and the fertilized egg usually implanted in about 6~7 days after intercourse, and it just implanted successfully, and the trophoblast cells secreted a relatively low concentration of HCG (human chorionic gonadotropin), so the test is not able to detect the pregnancy for the time being. Ovulation test paper is used to detect LH (luteinizing hormone peak), women in the ovulation period LH peak, ovulation test paper will detect a positive result, this can only determine whether the woman has ovulated, can not judge whether the woman after intercourse pregnancy. It is recommended that after 14 days of coitus, you take morning urine and use pregnancy test paper to test for pregnancy, which is a more accurate way to know whether a woman is pregnant or not, or you can go to the hospital to take blood to check the HCG value.