It stores the hormone levonorgestrel, a progesterone found in many other forms of contraception. It contains no estrogen and can be inserted or removed within just a few minutes in a physician s office. Mirena is different from oral contraceptives in that it releases one fifth to one eighth the amount of levonorgestrel, said Susan A. Ballagh, M.D., assistant professor of obstetrics and gynecology at EVMS and local investigator of the study. The hormone travels directly to the vaginal wall, not through the bloodstream, as with other forms of oral contraception. This hormone inactivates the lining of the uterus, typically leading to reduction of the menstrual flow of at least two-thirds, Ballagh said.
Some women stop ovulation altogether after the first three to six months of use.
The hormone also acts to thicken the cervical mucus, which can prevent sperm from entering the uterine cavity. The system is very effective for five years or until removed, Ballagh said. The EVMS site will register 20 healthy women in monogamous relationships who have at least one child but want no children within the year following the insertion of the system. Developed in Europe, the Mirena Intrauterine System has a very high success rate. In studies in Europe, only one of 1,000 women became pregnant.