The spring in the rim of the<unk> forms a seal against the vaginal walls. The<unk> covers the cervix, and physically prevents sperm from entering the uterus through the os. Traditionally, the<unk> has been used with spermicide, and it is widely believed the spermicide significantly increases the effectiveness of the<unk>  Insufficient studies have been conducted to determine effectiveness without spermicide. It is widely taught that additional spermicide must be placed in the vagina if intercourse occurs more than six hours after insertion. However, there has been very little research on how long spermicide remains active within the<unk>  One study found that spermicidal jelly and creme used in a<unk> retained its full spermicidal activity for twelve hours after placement of the<unk>  It has long been recommended that the<unk> 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<unk> (removal before 6 hours post-intercourse) has never been formally studied, and cannot be recommended. It has been suggested that<unk>  be dispensed as a one-size-fits-all device, providing all women with the most common size (70 mm). However, only 33% of women fitted for a<unk> are prescribed a 70 mm size, and correct sizing of the<unk> is widely considered necessary.
Diaphragm 
Epigastrium
Thoracic diaphragm
Airtraq
Gumma 
Ainhum
Azasteroid
Hippus