Why is it so hard to detect a pregnancy?

Pregnancy detection: A few days after conception, the fertilized egg attaches itself to wall of the uterus. This can cause one of the earliest signs of pregnancy spotting and, sometimes, cramping.That's called implantation bleeding. It occurs anywhere from six to 12 days after the egg is fertilized. If you miss your period, buy a pregnancy test to see if you are pregnant. Pregnancy should not be hard to diagnose.