The study, led by J. Christopher Carey, M.D., then of the University of Oklahoma, in Oklahoma City, appears in the February 24 New England Journal of Medicine.
"What was thought to be a promising experimental treatment is, in fact, ineffective for preventing preterm birth in pregnant women who have bacterial vaginosis but do not have symptoms," said Duane Alexander, M.D., Director of the NICHD. "Nonetheless, NICHD remains committed to identifying-and preventing-the causes of preterm birth."
Bacterial vaginosis is caused by several species of bacteria which replace the harmless Lactobacillus bacteria that normally live in the vagina, explained Mark Klebanoff, M.D., Director of NICHD's Division of Epidemiology, Statistics and Prevention Research, and an author of the study. In some cases, the harmful bacteria produce such symptoms as vaginal odor and discharge; but in others produce no symptoms. Researchers are unsure of how the condition is transmitted.
"We had hoped that treating bacterial vaginosis would prevent preterm birth but unfortunately that wasn't the case," Dr. Klebanoff said.
Bacterial vaginosis affects about 800,000 pregnant women each year in the U.S., and women with the condition are more likely than are other women to give birth prematurely, he added.
"If treatment of bacterial vaginosis could reduce this risk, as many as 80,000 preterm births could be prevented," Dr. Klebanoff said. "Similarly, the 4,000 deaths that result from premature birth, as well as the 4,000 cases of damage to the nervous system, could also be prevented."
For the study, the researchers treated 953 pregnant women with the antibiotic metronidazole, and 966 women with a placebo. The women received their first treatment between their 16th and 23rd weeks of pregnancy, and their second treatment between their 24th and 29th weeks of pregnancy. Bacterial vaginosis was eliminated in about 77 percent of the women who received the antibiotic, and about 37 percent of the women who received the placebo.
About 12 percent of the women in both groups gave birth prematurely. Similarly, more than 10 percent of the women whose vaginosis was eliminated by the antibiotic treatment gave birth prematurely, as did more than 10 percent of the women whose vaginosis was not eliminated.
"Clearly, treatment of bacterial vaginosis did not reduce preterm birth in our study," Dr. Klebanoff said.
Dr. Klebanoff noted that metronidazole treatment did not eliminate preterm birth in women who had a preterm baby in a previous pregnancy. Although there were not enough women in the NICHD study who had previously given birth prematurely to be a statistically significant group, the antibiotic treatment actually appeared to increase their risk for giving birth prematurely.
Dr. Klebanoff added that the study results do not completely rule out the effectiveness of metronizadole treatment under other circumstances. For example, it is possible that a longer duration of treatment might be needed. Similarly, treatment earlier in pregnancy might also produce different results. The study authors noted, however, that they sought to avoid exposing the fetus to metronizadole early in the first trimester, when the internal organs are forming. In addition, using metronizadole in combination with another antibiotic may also produce different results.
Dr. Klebanoff stressed, however, that such possible alternative treatments would need to be rigorously tested before they are tried in patients, to assure their safety and effectiveness.
"Although the literature consistently indicates that intrauterine infection and bacterial vaginosis are associated with preterm birth, the results of our study do not support metronidazole treatment of asymptomatic pregnant women with bacterial vaginosis regardless of whether they were otherwise considered at either high or low risk for preterm birth," the study authors wrote.
The NICHD is one of the Institutes comprising the National Institutes of Health, the Federal government's premier biomedical research agency. NICHD supports and conducts research on the reproductive, neurobiological, developmental, and behavioral processes that determine and maintain the health of children, adults, families, and populations. The NICHD website, http://www.nichd.nih.gov,
contains additional information about the Institute and its mission.