A class-action suit has been filed against three Rhode Island medical groups that implanted unapproved birth-control devices in hundreds of women. The suit names OB-GYN Associates, Bayside OB-GYN and the Center for Obstetrics & Gynecology as defendants, but leaves open the possibility of adding additional defendants as more are discovered. It was filed Wednesday in Superior Court, Providence, by personal-injury lawyer Ronald J. Resmini.