Using the drug metronizadole to treat pregnant women who have the sexually transmitted disease trichomoniasis does not reduce the women's chances for giving birth prematurely, and may actually increase them, according to a study appearing in the August 16 New England Journal of Medicine. The study was conducted by researchers at the National Institute of Child Health and Human Development (NICHD) Network of Maternal Fetal Medicine Units, collaborating with researchers at the NICHD .
"Although metronidazole appeared promising at preventing pre-term births due to trichomoniasis, that promise has not been realized," said Duane Alexander, M.D., Director of the NICHD. "This study suggests caution in the use of metronidazole when treating pregnant women."
Trichomoniasis is caused by infection with the microscopic organism Trichomonas vaginalis. Pregnant women infected with T. vaginalis are more likely to give birth prematurely, to give birth to children of low birth weight, and to give birth prematurely to children of low birth weight, explained the study's first author, Mark Klebanoff, M.D., Director of NICHD's Division of Epidemiology, Statistics, and Prevention Research. Moreover, children born to mothers with trichomoniasis are more than twice as likely to be stillborn or to die as newborns than are children born to women who do not have the disease.
In women, symptoms of trichomoniasis include burning, itching, and soreness of the vagina. Infected women may also experience pain during intercourse and urination. Many women, and most men, who have the infection do not experience any symptoms. Estimates of the trichomoniasis' frequency vary, said Dr. Klebanoff, but from three to 20 percent of women of child-bearing age may have the infection.
Because of the risks to infants whose mothers have trichomonas, some researchers have recommended that pregnant women who have the infection be treated with the antibiotic metronidazole. The current study-the largest, most comprehensive of its kind to date-tried to determine whether using metronidazole to cure T. vaginalis infection would indeed prevent the preterm labor associated with the infection. Only women who did not have symptoms of trichomoniasis were included in the study because the investigators felt it would be unethical not to treat the often-uncomfortable symptoms of the disease.
Of the 604 women who completed the study, 315 were treated with metronidazole and 289 were treated with a placebo. Delivery occurred before the 37th week of pregnancy for 60 women (19 percent) in the metronidazole group and for 31 women (10.7 percent) in the placebo group.
The researchers do not know why the women in the metronidazole group were more likely to give birth prematurely. One possible explanation they considered was that the death of the T. vaginalis organisms following treatment provoked an immune system response that stimulated early labor. The study authors added, however, that this was unlikely, because the last treatment with metronidazole took place at the 30th week of pregnancy-well before most of the preterm births among the women in the study--which occurred at the 35th and 36th weeks of pregnancy.
"This is clearly a dilemma for physicians," said Dr. Klebanoff. "Treating both infected women and their partners for trichomoniasis is a recommended public health measure. Yet our findings show that treating trichomoniasis in women without symptoms doesn't reduce the likelihood of premature labor, and may actually increase it."