Antibiotics Ineffective for Preterm Birth Prevention.

TORONTO -- Women at high risk of preterm delivery do not fare any better when they are given broad-spectrum antibiotics, according to results of a randomized, prospective study of more than 700 women.

In fact, women with a history of preterm delivery may actually do worse, Dr. William Andrews, the study's lead author, said at the annual meeting of the Society for Gynecologic Investigation.

"The injudicious use of an antibiotic intervention with the goal of preventing preterm birth is probably not advisable," said Dr. Andrews, professor and director of ob.gyn. at the University of Alabama, Birmingham.

More than 700 women with positive fetal fibronectin (FFN) tests (at least 50 ng/mL) between 21 and 25 weeks' gestation were randomly assigned to receive either 250 mg oral metronidazole three times a day plus 250 mg oral erythromycin four times per day for 10 days or placebo.

Previous studies have shown that a silent upper genital tract infection with any of about 30 types of bacteria usually found in the lower genital tract is strongly associated with a high risk of premature delivery. The particular antibiotics used in the study were chosen because they are effective in treating these 30 types of bacteria.

There was no significant difference in the rate of preterm delivery before 37 weeks' gestation. The rate was 14.4% in the 347 treated women vs. 12.4% in the 355 women on placebo.

"It could be that once the silent infection has advanced to the point where the FFN is detectable in the cervix or vagina, it may be too late for a simple antibiotic intervention to be effective. Or perhaps there are different bacteria responsible, which are not covered by these antibiotics. Or maybe the course of ...