If your period is usually regular and you have not had your period for more than 3 days, it is possible to detect it with an early pregnancy test. After having intercourse during ovulation, the sperm and egg unite to form a fertilized egg, which takes about 12 days on average before it enters the uterine cavity. The fertilized egg does not settle immediately after entering the uterine cavity, but has to find a suitable location before it will settle and grow. After it settles, the trophoblast cells will secrete blood HCG, and it is only at this time that the pregnancy can be detected by urine test. If you have had your period for more than 3 days, you can use morning urine to test for pregnancy and do not drink too much water before the test to avoid diluting the urine and affecting the results.