IUDs and infertility [Authors reply] [letter]

Drs. Lippes and Grubb express concern that the authors finding of a greater risk of primary tubal infertility for women used the Lippes Loop or Saf-T-Coil than for women who used copper IUDs may be erroneous because "the longer period of availability of the plastic devices means that in general infertile women who had used plastic devices have a longer time to be referred to a clinic (and thus to be enrolled as cases) than infertile women who have used copper devices." This hypothesis while reasonable fails to explain the finding. In the authors study each infertility case was matched with a control of similar age whose 1st child was born during the calendar year after the year in which the case first began trying unsuccessfully to become pregnant. The analysis then focused on IUD use and other events that occurred before the approximate date when the case and her control started trying to conceive (the "reference date"). Thus the "time for referral" of the infertility cases that concerns Drs. Lippes and Grubb was the interval from the reference data to the date of initial evaluation for infertility. The mean "time for referral" was nearly identical for the cases who had used the Lippes Loop or Saf-T-Coil (2.1 years) and the cases who had used copper IUDs (2.0 years). The mean intervals from first IUD use to the reference date were also similar (4.3 years for the cases who had used the Lippes Loop or Saf-T-Coil; 3.5 years for the cases who had used copper IUDs). The data indicate that differences in "time for referral" fail to account for the finding that users of the Lippes Loop or Saf-T-Coil are at reater risk of infertility than users of copper IUDs. The letter of Drs. Lippes and Grubb prompted other analyses that may be important with regard to the risk of infertility for women who use copper IUDs. Among the women whose 1st IUDs were inserted during or after 1975 equal proportions of cases and controls had used only copper IUDs; none of these women had undergone a reinsertion and the mean duration of use for both the cases and controls was well within the 3-year limit currently recommended for replacement of copper IUDs. Among those women whose 1st IUDs were inserted before 1975 there were 5 cases as compared with only 1 control who had used only copper IUDs without any reinsertions. Although the number of cases is small the study suggests that copper IUDs may increase the risk of infertility if left in place longer than the recommended time. As Dr. Hasson points out there appear to be causal pathways leading to tubal infertility that do not involve infection e.g. those that involve endometriosis.