If you were designing a perfect family planning method, what characteristics should it have? Certainly, the method would be highly effective and safe. Probably it should be designed for women, since they are usually more interested than men in controlling fertility. It would be nice if the method also had some beneficial side effects such as making periods lighter and less painful. Fortunately such a method is now available!
I have known about Mirena® for several years. Doctors in other countries, who have many years’ experience with it, have raved about it. The FDA finally approved it for use in the United States in 2000. It is wonderful to have another option for American women. As effective as tubal ligation, it is temporary and can be removed easily if a woman wishes to conceive.
Mirena® is made out of soft plastic in the shape of a “T”. The stem is filled with levonorgestrel, a potent form of progesterone—the hormone of pregnancy. A tiny amount of the hormone passes continually through the plastic into the uterus. It contains enough to last five years. Fortunately, although the levonorgestrel has a direct effect on the uterine lining, very little gets into the woman’s blood stream. Most women have no generalized symptoms from the hormone.
But isn’t this an Intrauterine Device (IUD)? Aren’t IUDs dangerous? Well, one IUD—the Dalkon Shield—was a disaster. Many years ago it was rushed to market before they had sufficient time to test it well. It made women vulnerable to serious infections, and some became infertile from the Dalkon Shield.
Two IUDs are now available in the United States, and both are amazingly safe. A woman who is in a mutually monogamous relationship is the best candidate for an IUD. Furthermore, IUDs work best for women who have given birth, since pregnancy stretches the uterus a bit. A potential user should be well informed about IUDs, and she should learn how to check that it is in the proper position. The device must be inserted skillfully by a qualified doctor or nurse.
How does Mirena® function? The levonorgestrel makes it more effective than other IUDs. Because the hormone causes the uterine muscle to relax, it also decreases cramps. The hormone prevents pregnancy in at least two ways. The principal way that it works is that it makes cervical mucus thick and sticky so that sperm cannot pass through. It also thins out the lining of the uterus. If a sperm got past the inhospitable cervical mucus and an egg did get fertilized, it would be unlikely to implant. This thinning effect also makes bleeding lighter or stops it completely.
One way of looking at Mirena® is that it is a means of getting the hormone where it can work most effectively. Because the hormone is released inside the target organ, only a tiny amount is needed, and side effects are minimized. One advantage of any IUD is that the user is constantly protected against pregnancy without having to do anything on a regular basis.
Levonorgestrel can cause a few annoying side effects. Certain women complain of increased acne or headaches, and rarely they will have breast tenderness or nausea. Some women stop having periods entirely, which is normal for a Mirena® user, as long as the device is in place. Fortunately, it does not cause weight gain.
Mirena® is small and flexible, which makes it well tolerated even by women who haven’t had a baby. The other popular IUD, Paragard®, is a bit larger and stiffer. Although Paragard® lasts longer than Mirena®—ten years versus five—women do not tolerate it as well if they haven’t started their family yet. In fact, young, childless women have requested many of the Mirenas® that I have placed so far.
Mirena® is called an IntraUterine System (IUS). I think that this is a marketing ploy to distinguish it from other IUDs. It is also possible that the manufacturer is preparing to market it for other indications. In many countries it has been used to help women who suffer from excessive bleeding or bad menstrual cramps. In addition, it prevents abnormalities of the lining of the uterus (including cancer), especially in menopausal women on estrogen. Although the FDA hasn’t approved Mirena® by for noncontraceptive uses, women welcome it for help with these problems.
At last we have an IUD that has a very low failure rate, few side effects and many benefits. Mirena® has great potential to help women control their fertility and deal with other problems.
© Richard Grossman MD, 2005
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