Intrauterine Contraceptive Devices

The intrauterine device (IUD or IUCD) is made of plastic or metal or a combination of these materials. It is introduced into the endometrial cavity through the cervical canal. A large variety of shapes and sizes have been tried, with varying degrees of contraceptive effectiveness.

At the present time, only 3 IUDs are available for use in the U.S.: the Progestasert, the Copper TCu380A (Paragard), and a levonorgestrel-releasing system (Mirena) (Fig 33-3). The Progestasert is made of a special polymer that contains a reservoir of 38 mg of progesterone, which is released at a rate of 65 g per day. However, due to this design, the useful lifespan of this device is only 1 year. The Paragard is wound with copper wire that creates a surface area of copper of 300 mm² on the vertical arms and 40 mm² on each of the transverse arms. The lifespan of this device is at least 10 years.

Recently, an intrauterine system containing levonorgestrel (released at 20 ug/d; Mirena) has been approved for use in the U.S. It provides contraception for up to 5 years. When compared to the copper TCu380A and Norplant, it was found to be just as effective for contraception but also more likely to cause amenorrhea, which in some patients is a benefit. Hormonal side effects such as depression, acne, headache, and weight change may also occur.

Just how IUDs act to prevent conception is not known. The most widely observed phenomenon is mobilization of leukocytes in response to the presence of the foreign body. The leukocytes aggregate around the IUD in the endometrial fluids and mucosa and, to a lesser extent, in the stroma and underlying myometrium. It is hypothesized that the leukocytes produce an environment hostile to the fertilized ovum. In laboratory animals, this leukocytic infiltration apparently is not dependent on microbial invasion. In human beings, the uterine cavity sterilizes itself, usually within 2-4 weeks after the device is inserted. Other theories regarding the mechanism of action are spermicidal activity with copper devices, disruption of endometrial maturation with the progesterone-releasing device, alteration of normal tubal cilial action, and even disruption of normal oocyte maturation. In short, the mechanism of action is not established. Furthermore, there are no data to suggest that a major mechanism of action may be that of an abortifacient.

Efficacy with the Paragard device is high, with a failure rate of less than 1% per year with prolonged use. In contrast, the Progestasert has a failure rate of about 1-1.5% with 25% of the pregnancies being ectopic. These data suggest that the latter device, unlike many contraceptive choices, offers no protection against extrauterine pregnancy.

It is felt by many practitioners that it is best to insert an IUD during a menstrual period because the cervical canal is fully patent then and the patient is least likely to be pregnant (). Furthermore, the endometrial cavity may be more distensible at this time in the cycle, and uterine cramps, if they occur as a result of insertion, will be less noticeable. However, insertion can be accomplished at any other time if this is desired or more convenient for the patient.