Fifteen days after intercourse and four days after the menstrual period did not detect pregnancy may be due to the fact that there is no pregnancy, the test time is too early, the use of the pregnancy test stick is not correct and other reasons. 1. not pregnant: it is not always possible to get pregnant if you have sex, if you have sex during the safe period, the chances of getting pregnant are very small. 2. The test is too early: the pregnancy test is to detect the value of chorionic gonadotropin in the urine, this hormone is produced by the placenta, the sperm and the egg after the combination of successful conception of about seven days before the beginning of secretion, the beginning of the amount of very little, it is not easy to detect. 3. pregnancy test stick is not used correctly: first of all, we should check whether the pregnancy test stick is a qualified product, whether in the shelf life, in addition to the proposal to use the first urine in the morning to test. If fifteen days after intercourse and four days after the passage of the pregnancy test did not detect pregnancy, it is recommended to consult a doctor in a timely manner, under the guidance of the doctor to further improve the blood HCG and other tests to clarify whether the pregnancy.