An intravaginal controlled-release prostaglandin E2 pessary for cervical ripening and initiation of labor at term. - Rayburn,W.F.; Wapner,R.J.; Barss,V.A.; Spitzberg,E.; Molina,R.D.; Mandsager,N.; Yonekura,L. (Obstet Gynecol, 1992)