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Mechanism of action of intrauterine contraceptive devices

      To the Editors:

      Spinnato (Spinnato JA II. Mechanism of action of intrauterine contraceptive devices and its relation to informed consent. AmJ Obstet Gynecol 1997; 176: 503-6) seeks revision of intrauterine contraceptive device (IUD) informed consent to emphasize the device's putative postfertilization inhibition of uterine implantation, as may sometimes occur after midcycle postcoital insertion. He claims for ordinary IUD usage that “There is little compelling evidence to suggest that copper IUDs reliably eliminate the likelihood of fertilization” but fails to cite any of the four principal reviews on the copper IUD's strong effects in reducing fertilization. One missed review demonstrates the direct, deleterious effects of copper on sperm motility and on sperm penetration into cervical mucus and shows that copper IUDs induce head tail separations in the few sperm reaching the oviduct.
      • Ortiz ME
      • Croxatto H
      Mode of action of IUDs.
      Another missed review summarizes statistical evidence of significant reductions in the percentage of IUD users with fallopian tube sperm shortly after intercourse, with greater reductions associated with copper IUDs.
      • Sivin I
      IUDs are contraceptives not abortifacients: a comment on research and belief.
      This review also reanalyzed primate data, in IUD-fitted macacques, finding no increase compared with control cycles for the same animals in the proportion of failed implantations but a statistically significant increase in proportions of midcycle inseminations without traces of fertilization.
      Demonstration of the reduction in fertilization rates in women with IUDs by study of the developmental status of ova in the oviducts of IUD users and of controls is weak, according to Spinnato, because some eggs “were actually not classifiable and could have been fertilized.” There is no ambiguity, however, between the 15% of controls and 64% of IUD subjects who had, unambiguously, no signs of development (no fertilization) (p < 0.01).
      • Sivin I
      IUDs are contraceptives not abortifacients: a comment on research and belief.
      Spinnato believes that the high IUD ratio of ectopic to total pregnancies results from prevention of implantation. However, the still higher ectopic ratio associated with tubal ligation, with no known mode of postfertilization action, shows that this argument is fallacious. The critical observation about ectopic pregnancies and IUDs is their annual rate. For the sole copper IUD available in the United States today the rate is 0.2 to 0.4 per 1000 women per year, 5% to 10% of the rate in women not using contraception. A 90% to 95% reduction in ectopic pregnancy rates by this copper IUD is a powerful indicator of sharply reduced risks of fertilization.
      A truly informed consent should be unbiased. An unbiased review of copper IUD actions, with the device in situ before coitus, would find its primary action is to prevent fertilization, chiefly by cytotoxic effects on sperm.

      References

        • Ortiz ME
        • Croxatto H
        Mode of action of IUDs.
        Contraception. 1987; 36: 37-53
        • Sivin I
        IUDs are contraceptives not abortifacients: a comment on research and belief.
        Stud Fam Plann. 1989; 20: 355-359