It is possible to detect pregnancy on the fourth day after intercourse. This is because at this time, if you are already pregnant, the sperm and egg have already combined, and the level of human chorionic gonadotropin in the body will start to change, so at this time, it is possible to detect pregnancy. However, because of the relatively short period of time, the level of human chorionic gonadotropin in the body may not have reached the concentration of the test, so the accuracy is relatively not very high, and this is also possible if the pregnancy has been confirmed at the time of the test. So at this time, a pregnancy detected is a confirmed pregnancy, but if it is not detected, it does not necessarily mean that there is no pregnancy. It usually takes more than a week after intercourse for the pregnancy test to be more accurate.