There are several factors that have to come together before you are sure that you are pregnant. First of all, you need to have unprotected sex within the time that you are most fertile. This is usually in the middle of your menstrual cycle, at the time when you are ovulating. When you are not fertile, there is no egg being released from your ovaries and even as you will have sperm within your reproductive system no fertilization will take place and no pregnancy test will come in positive. You must be ovulating for a pregnancy test to come in positive. Also, you cannot have unprotected sexual contact and test for pregnancy the same day. It takes an average of three days for the sperm to travel through the uterus to meet with the egg in the fallopian tube. You should wait for fertilization to take place and for the fertilized egg to become implanted into your uterus. This will take a total of five to six days after having unprotected sex. Itsi also the time that your body will be producing the pregnancy hormone called human gonadotrophin hormone that is responsible for the life of the pregnancy-it will be resent in blood and urine samples. Essentially, this is the hormone that pregnancy tests will test for; whether blood or home pregnancy test kits.