Clinical characteristics of the study population according to the study period
During the study period, a total of 1,460 women were eligible for this study. Table 1 summarizes the comparison of maternal ESBL-E vaginal colonization according to the study period. The overall maternal ESBL-E vaginal colonization rate was significantly higher in period 2 than in period 1 (6.2% vs 2.4%, P < 0.001). Notably, the positivity rate for E. coli colonization (14.3% vs 6.3%,P < 0.001) and the rate of ESBL-E-positive E. coli colonization were significantly higher in period 2 than in period 1 (5.3% vs 1.7%, P < 0.001). However, there was no significant difference in the rates of K. pneumoniae colonization and ESBL-E-positive K. pneumoniae colonization between periods 1 and 2.
Table 2 compares the maternal baseline characteristics according to the study period. The maternal age, primiparity, pre-pregnancy body mass index, IVF-embryo transfer pregnancy rate, and short CL rate were significantly higher in period 2 than in period 1. In particular, the prior antibiotic treatment rate within 4 weeks was significantly higher in period 2 than in period 1 (18.5% vs 13.9%, P = 0.018). We additionally checked the indications for antibiotic use among the women with prior antibiotic treatment (n = 238). Suspected diagnosis or confirmed diagnosis of pPROM (n = 160) was most often indicated, followed by PTL, prophylactic antibiotic use before or after cerclage, IIOC, and fever, as shown in Table 2. No significant difference was observed for any indication between the two periods.