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      To the Editors:

      Editorial requirements of the American Journal of Obstetrics and Gynecology required me to reduce my references from 61 to 25. I did not “miss” articles but was required to restrict my citations.
      Sivin misquotes me. Throughout my article I acknowledge a spermicidal effect of IUDs. The issue I addressed was whether, as some recent authors have suggested, the available evidence supports a claim of exclusivity of this action. There is clear and compelling evidence for a postfertilization mechanism of action of IUDs that refutes such claims.
      Sivin objects to my criticism of Alverez et al.
      • Alvarez F
      • Brache V
      • Fernandez E
      • Guerrero B
      • Suiloff E
      • Hess R
      • et al.
      New insights on the mode of action of intrauterine contraceptive devices in women.
      My concerns as indicated in my article remain firm. Sivin displays unreasonable confidence in a single cycle study of nine IUD users with uncontrolled timing and certitude of insemination (excluding five patients with ambiguous results).
      Sivin argues that evidence of an increased risk of ectopic gestation after tubal ligation is somehow pertinent to this issue. Analogies are inherently weak arguments, and this one is particularly so. The mechanism of ectopic pregnancy after tubal ligation (mechanical injury to the tubes) is not particularly pertinent.
      Sivin claims that there is a 90% to 95% reduction in ectopic pregnancy among copper IUD users. He provides no reference. In a study on ectopic pregnancy, Ory
      • Ory HW
      The Women's Health Study, ectopic pregnancy and intrauterine contraceptive devices: new perspectives.
      more modestly estimates a 60% reduction in ectopic risk among IUD users versus uncontracepted control patients. An extrapolation of this data would leave potentially 40% of an IUD's mechanism as postfertilization, a major portion. This is, at best, a rough estimate.
      If Sivin is citing his own study
      • Sivin I.
      • Copper T
      IUD use and ectopic pregnancy rates in the United States.
      of 35,496 insertions of copper-bearing IUDs, the limitations of this study should be noted. Fewer than one half of patients (15,244) were deemed to have had adequate follow up. What happened to the other 18,000+ patients is unknown. Most of the patients received their continuing health care at a different site. The bottom line is that one cannot conclude what the ectopic rate might be with such poor follow-up.
      For prevention of fertilization to be the “primary” mechanism of action of IUDs, as Sivin states, requires that mechanism to explain just >50% of the action. This would still allow prevention of implantation to remain a major mechanism of action for IUDs, and that's the point. Information to practitioners and informed consent to patients should reflect this.

      References

        • Alvarez F
        • Brache V
        • Fernandez E
        • Guerrero B
        • Suiloff E
        • Hess R
        • et al.
        New insights on the mode of action of intrauterine contraceptive devices in women.
        Fertil Steril. 1988; 49: 768-773
        • Ory HW
        The Women's Health Study, ectopic pregnancy and intrauterine contraceptive devices: new perspectives.
        Obstet Gynecol. 1981; 57: 137-144
        • Sivin I.
        • Copper T
        IUD use and ectopic pregnancy rates in the United States.
        Contraception. 1979; 19: 151-173