You will have to take about a week, since this is the average time it takes for implantation to take place. You will never get a positive pregnancy test as soon as you have sex and if this happens then the positive test will be as a result of sexual contact that took place some week or so earlier. Women with multiple partners will be able to know who among their partners is the father of the baby they are carrying, and during this time they can also get a DNA test performed on the uterus. Anyhow, the sperm will take about three days to travel to the egg in the fallopian tube to fertilize it and take a further three days to travel back and get implanted into the uterus. It is as this time that the human chronionic gonadotrophin hormone will be released to assure the life of the pregnancy, and this will cause it to bring about the imbalance that causes the pregnancy symptoms of tiredness, breast tenderness and the lack of menstrual periods. Most women will wait for their periods to delay for them to test for pregnancy, which is one way of estimating how far long they are in their pregnancy.