Impact of interconception antibiotics on the endometrial microbial flora

Objective The purpose of this study was to evaluate the impact of an interconception antibiotic regimen on endometrial microbial flora and histologic type. Study design This was a secondary analysis of a double-blind randomized placebo-controlled trial of prophylactic metronidazole plus azithromycin that was given to 241 women (antibiotics, 118 women; placebo, 123 women) with a previous preterm delivery to prevent recurrent preterm delivery. Endometrial cultures and histologic types were obtained at randomization and 2 weeks after treatment. The prevalence of either the new acquisition or the resolution of individual microbes, categories of microbes, and plasma cell endometritis were compared by chi-square or Fishers’ exact tests. Results Overall, antibiotics were associated with lower acquisition and higher resolution of microbes. Of women without Gardnerella at baseline, 14% of the women who received antibiotics vs 34% of the women who received placebo had positive endometrial culture for the organism after treatment ( P < .05); of those women with G vaginalis at baseline, 57% of the women who received antibiotics vs 33% of the women who received placebo ( P < .05) had a negative follow-up culture. Other gram-negative rods, especially aerobes in general, manifested similar patterns. The impact on anaerobes and plasma cell endometritis was not definitive, but there was a trend toward the increased resolution of the former (77% vs 55%) and reduced acquisition of the latter (28% vs 50%). Conclusion The antibiotic regimen prevented the acquisition and promoted the resolution, but not the eradication, of gram-negative rods such as G vaginalis and the aerobic subcategory.