It has long been recommended that the diaphragm be left in place for at least six or eight hours after intercourse. No studies have been done to determine the validity of this recommendation, however, and some medical professionals have suggested intervals of four hours or even two hours are sufficient to ensure efficacy. One manufacturer of contraceptive sponges recommends leaving the sponge in place for only two hours after intercourse. However, such use of the diaphragm (removal before 6 hours post-intercourse) has never been formally studied, and cannot be recommended.