Pregnancy can be detected even if you have not had your period. HCG is a protein hormone secreted by the trophoblast of the placental syncytium, and the placenta only begins to secrete HCG on the seventh day after the formation of the fertilized egg. It is generally recommended to have a blood test for HCG on the tenth day after sexual intercourse; if conception has occurred, the HCG will definitely be elevated; if the HCG is not elevated on the tenth day after sexual intercourse, it means that there is no pregnancy. A woman’s ovulation day is 14 days before her next menstrual period. If you have sex after ovulation, you will be able to detect pregnancy at the latest 10 days before your period arrives, so it is possible to find out if you are pregnant before your period arrives.