Implantation cramps are felt anywhere from a week to a few days before your period is due according to WebMD. If an embryo is fertilized, it will implant in the uterus anywhere from 7 to 12 days after you have ovulated. Implantation cramps may feel very similar to menstrual cramps.
Once the embryo has implanted, your body starts producing human chorionic gonadotropin, also known as hCG. This hormone is detected by pregnancy tests; it also tells your body that you are pregnant. Another sign of implantation is light spotting. The spotting is due to the embryo burying itself into the wall of the uterus. Implantation bleeding can be light pink, light red or brown.