Users of intrauterine devices are twice as likely to become infertile as women who do not use the birth control devices, researchers said Wednesday.
Authors of two new studies sponsored by the National Institute of Child Health and Human Development said their findings provide the first direct evidence that tubal infertility is linked to the use of IUDs.
Tubal infertility occurs when a woman’s Fallopian tubes are blocked, preventing an egg from traveling from the ovary to the uterus.
Researchers said that, of the 550,000 current cases of tubal infertility nationwide, 16% or 88,000 may have resulted from use of IUDs, which can cause pelvic infections and damage the tubes. An estimated 2.2 million U.S. women use the devices.
The studies “confirm what doctors have strongly suspected for years,” said Dr. Bruce V. Stadel, medical officer at the institute, adding that until now “we haven’t known just how often different types of IUDs lead to infertility.”
The findings, which were published in the New England Journal of Medicine, said that the Dalkon Shield and other plastic IUDs carry the most risk of causing infertility and that those made with copper present the least risk.
The research indicated that IUD users who have never had children run a greater risk of infertility than mothers who use the devices. IUDs can be a reasonable option for women who have been pregnant, said Stadel and two other authors of the two studies, who discussed their findings at a news conference Wednesday. The studies indicate that overall the tubal infertility rate is twice as great for IUD users as for nonusers.
Dr. Daniel W. Cramer of the Harvard Medical School’s obstetrics and gynecology department said: “I believe that use of an IUD by the woman who has never had a child is not a method of first choice (of birth control), even the copper devices.”
Janet R. Daling, an associate professor at the University of Washington’s school of public health and community medicine, said women who eventually want to have children “should use some other method.”
The first study, headed by Daling, involved Seattle fertility specialists and compared the rates of IUD use in 159 childless women who have experienced tubal infertility with the rates of 159 new mothers.
Infertility Centers Surveyed
Cramer led the other study, which was based in Boston and surveyed seven infertility centers and hospitals, mostly in the East. That study compared IUD use in 283 childless, infertile women with 3,833 new mothers.
Women using the Dalkon Shield, which was withdrawn from the market in 1974 amid claims that the device caused severe pelvic infections, were three times as likely to become infertile as women who had not used any IUDs, Cramer’s study concluded. Daling’s study said women who use the Dalkon Shield were seven times as likely to become infertile.
Both ranked two other brands, the plastic Lippes Loop and Saf-T-Coil, next, at about three times the risk of women who do not use IUDs. Devices made with copper, such as the popular Copper-7, carried a risk of two times or less.
Daling’s study said there is “very little excess risk” in the devices made with copper, which researchers said may be safer because the metal helps kill harmful bacteria.
Other Factors Involved
The researchers also found that previous pelvic infections, smoking and multiple sex partners seemed to contribute to infertility.
IUDs, the object of controversy since their introduction in Germany more than 50 years ago, were studied in the 1970s and found to cause an increase of three-fold to five-fold in the risk of pelvic inflammatory disease.
However, problems with this earlier research were cited in an editorial accompanying the current studies. The editorial said that many of the earlier studies used control groups that included women who use contraceptives, condoms and diaphragms, “each of which offer substantial protection” against the development of a pelvic infection called salpingitis.
Although the research focused mainly on infertility in women who have never had children, the Boston-based study also examined “secondary infertility,” in which women who have had one child cannot conceive another.
Stadel, explaining why such studies had not been done before, said the issue required “extensive exposure in the population before we could study it.”
But he conceded that, if laboratory testing had been required on the Dalkon Shield and other devices before Congress passed a law to that effect in 1975, “some of the concerns about the differences between the Dalkon Shield and other devices could have emerged earlier.”