Implantation cramping, which occurs as the uterine mucous membrane melts around the place of implantation, happens as early as a week after ovulation and generally ceases in a few days, states Babies Online. Implantation cramps occur once or over the course of a few days, though some women experience none.
Because implantation cramps are associated with the fertilized egg attaching to the uterine wall, these initial cramps only last a few days, explains Implantationbleed.com. Cramping after the initial implantation is generally associated with stretching of the uterus and surrounding muscles that support the growing baby. Such cramps are sometimes experienced throughout a pregnancy as the stretching continues. Report extreme or persistent cramps to a doctor to be sure that they are not a sign of illness.