Original sentence: All second-generation copper-T IUDs have failure rates of less than 1% per year, and cumulative 10-year failure rates of 2-6%.Hormonal contraceptives reduce the risk of developing pelvic inflammatory disease (PID), a serious complication of certain STDs.IUDs, by contrast, do not   protect against STDs or PID.Some barrier contraceptives protect against STDs.The presence of a device in the uterus prompts the release of leukocytes and prostaglandins by the endometrium.These substances are hostile to both sperm and eggs; the presence of copper increases this spermicidal effect
Edited sentence: It's known however that the presence of a device in the uterus prompts the release of leukocytes and prostaglandins by the endometrium.Second-generation copper-T IUDs have failure rates of less than 1% per year, and cumulative 10-year failure rates of 2-6%.The mechanism of IUDs is not well understood.These substances are hostile to both sperm and eggs; the presence of copper increases the spermicidal effect