Intrauterine devices work primarily as a foreign body stimulating the immune system into producing an excess of leukocytes and prostaglandins. This creates a hostile environment in the uterus and fallopian tubes, making it difficult for fertilization to occur. In addition, the IUD creates a barrier to implantation of an embryo into the endometrium. Because the contraceptive effect may occur after fertilization some women find this form of family planning unacceptable. Most IUDs are now made of a plastic frame, with copper wrapped around them to increase their contraceptive action and therefore reduce the failure rate. Threads are usually attached to the lower end to facilitate removal. They are extremely reliable, with pregnancy rates of less than 1 per 100 women using them for a year. However, they are not very effective at preventing ectopic pregnancies which develop outside the uterine cavity. IUDs can also be used as ‘emergency’ contraception up to 5 days following the calculated date of ovulation.
Coils, as they are commonly known, are not usually recommended for women who have never been pregnant, as they are more difficult to insert and the slightly increased risk of pelvic inflammatory disease (PID) may impair future fertility. They are also unsuitable for women with a recent history of sexually transmitted disease or multiple sexual partners. Women with an abnormally shaped uterus, possibly caused by fibroids, should use a different contraceptive technique as the risks of failure are much higher in this situation.
The recent development of progestogen-releasing IUDs has been an exciting new contraceptive advance. Difficulties associated with older generation coils, such as heavy and sometimes painful periods, promise to be overcome. They have also provided a new treatment option for women with heavy periods who no longer need contraception, perhaps because they have already been sterilized. This type of IUD can be used to oppose the unwanted effects of oestrogen on the endometrium in women receiving hormone replacement therapy (HRT).
Andrew Hextall, and Linda Cardozo
See also contraception.
intrauterine device (IUD), variously shaped birth control device, usually of plastic, which is inserted into the uterus by a physician. The IUD may contain copper or levonorgestrel, a progestin (a hormone with progesteronelike effects; see progesterone). Apparently the IUD creates a hostile environment for the fertilized egg.