Contraceptive sponges are not as effective as other forms of contraception, we advise that they are an excellent form of back up contraception, as they have spermicide which can act as protection against infections as well as pregnancy.
Knowing it left the market after about of decade of use, many didn't notice when the sponge slipped back into availability in 2005. As a contraceptive by itself the sponge has a much higher failure rate than most women would want from their contraception.
It's important to get that sponge wet before use, it is supposed to be moistened with 2 tablespoons of water and squeezed once, and as a gyno I like cleaver ways to remember to do that so I tell the patients to remember to "bob their sponge" and it's easy to remember! I also like the fact that as a polyurethane product, allergic reactions are less likely to get. You do have to remember your water "bob" has to be done a bit in advance, place the sponge in the vagina about 30 minutes before use, you must leave it for 6 hours after sex, and really not more than about 30 hours. Women who have had children before get a bit more slippage than women who have not, so their failure rate is almost double that of the women who have not delivered before. Although the wet "bobbbed" sponge has active spermacide, it's not been shown to be an effective protection against STDs, and for that you need a condom.