Implantation bleeding is a common cause of spotting early on in pregnancy. Implantation bleeding happens when the fertilized egg attaches to the uterine lining. This can trigger a few days of light bleeding or spotting. This spotting often occurs before a woman even knows she is pregnant and is often mistaken as a pending period. Bleeding that occurs after the day a woman expects her period is typically too late to be considered implantation bleeding, and is more likely related to early pregnancy in general.