Yay, that's an interesting question!
As we've discussed before, the woman is not technically pregnant for the first 2 weeks of pregnancy. That's why the 3rd week of the pregnancy is simultaneously the 1st week of your baby's existence! 
Your child's life begins at the moment of fertilization, which happens within 24 hours of ovulation. An egg is released into the Fallopian tube during ovulation, where it finally meets the sperm. If everything goes well, the fertilized egg starts its journey along the Fallopian tube, down to the uterus lining. The egg, which is now a bundle of quickly dividing cells, finds its nesting place around 7–9 days after conception — that is, between the 3rd and the 4th weeks of pregnancy. That's when the hCG level in your body starts to rise, and the performed test will show a positive outcome. At this time, the first symptoms of pregnancy may begin to show — you may notice light bleeding or spotting caused by the egg latching onto the uterus's wall.
Read more