A double-blind cross-over study of the effect of doxycycline on mycoplasma infection and infertility

Forty-two couples in an infertility clinic were examined for genital infection with Mycoplasma hominis or Ureaplasma urealyticum (T strains). In 21 couples one or other partner was found to be infected; no chlamydiae, trichomonads, or gonococci were isolated from any of these couples. All patients were then included in a double-blind crossover doxycycline/placebo study lasting 8 months. Pregnancy was achieved in one of the 21 couples who were free of infection. Of the 21 couples who were infected, one achieved a pregnancy while still infected, and 19 lost their infection on doxycycline, of whom four achieved a pregnancy. These four pregnancies all occurred among the 10 couples who received doxycycline first. One further pregnancy occurred after the trial was over. Since 5 of the 7 pregnancies occurred in the first 4 months of the trial, they were probably due to the psychological effect of treatment rather than the effect of the drug on infection.