Pregnancy can be detected less than a month after intercourse. Generally, a week after intercourse, the trophoblast layer of the fertilized egg secretes human chorionic gonadotropin, and at this time, blood can be drawn to test for human chorionic gonadotropin to determine if you are pregnant. If the chorionic gonadotropin level in the blood is elevated, pregnancy is indicated. In addition to a blood test for chorionic gonadotropin, you can also test for pregnancy with an early pregnancy test or a pregnancy test. You can also use ultrasound to determine if you are pregnant. Generally, you can check for a gestational sac in the uterine cavity about one month after intercourse.