According to Mayo Clinic, implantation bleeding is a small amount of light spotting or bleeding that happens approximately 10-14 days after fertilization. Implantation bleeding is considered common and not considered a sign of a problem. This phenomenon is thought to happen when the developing embryo attaches to the lining of the uterus, or endometrium. The timing of when this happens is usually close to the missed period date and can be confused with a light period. This can lead to mistakes in determining due date and gestational age (how far along you are in weeks). Some women don’t have implantation bleeding, and some don’t notice it. Either way, an ultrasound is a good way to find the accurate due date and gestational age. Implantation bleeding stops on its own and doesn’t need any treatment. If you’re concerned about any vaginal bleeding during pregnancy, contact your doctor.