A randomized, blinded, placebo-controlled trial of antibiotics in idiopathic preterm labor.

Because subclinical genital tract infection may play a major role in preterm birth, the efficacy of adjunctive antibiotic therapy in combination with standard parenteral tocolysis was examined in a randomized, blinded study of patients with idiopathic preterm labor. Labor was documented by three contractions in 20 minutes, cervical dilation of 1 cm or more, and the need for parenteral tocolysis. Enrollment was restricted to patients with intact membranes and without known causes for preterm labor. One hundred three patients at 24-34 weeks' gestation were randomized to intravenous ampicillin plus oral erythromycin or corresponding placebos. Compared with the placebo group, the adjunctive antibiotic group had a similar frequency of preterm birth (38 versus 44%), time to delivery (34 versus 34 days), birth weight (2847 versus 2855 g), and episodes of recurrent labor requiring parenteral tocolysis (0.43 versus 0.49). In our population, we found no benefit to the adjunctive use of ampicillin plus erythromycin. Significant differences in genital microflora between our patients and those of other studies may explain our results.