It acts as a barrier, trapping the sperm within, and not allowing it to enter the cervical canal. A fresh condom has to be used every time a couple has sex. As condoms are not very expensive, this does not pose a problem. One complaint against condoms is the reduced sensitivity experienced during sex. Tearing of the condom during sex is also a rare risk.
Condoms are almost always successful in preventing pregnancy.
They are also useful for guarding against sexually transmitted diseases, the HIV virus and carcinoma of the cervix. This is a dome-shaped rubber device, which has to be inserted into the vagina, until it covers the anterior vaginal wall and the cervix. A diaphragm acts as a barrier to sperm. It is even more effective when used in combination with a spermicidal cream or jelly. The effectiveness of a diaphragm depends on leaving it in place for 6 six hours after sex and introducing more spermicide if sex occurs again.