Study population
This retrospective cohort study included consecutive pregnant women who were admitted to the high-risk pregnancy unit of our institution between 14+0/7 and 35+6/7 weeks of gestation and delivered a baby at our hospital. The indications for admission were preterm premature rupture of membrane (pPROM), preterm labor (PTL), incompetent internal os of the cervix (IIOC), and short cervical length (CL) (defined as a CL of <25 mm on transvaginal ultrasound). The study period was from January 2010 to December 2020 and was arbitrarily divided into period 1 (January 2010 to July 2015) and period 2 (August 2015 to December 2020) to evaluate changes in the association of ESBL-E vaginal colonization over the time periods. The study was approved by our institutional review board (no. 2020-08-006). The requirement for written informed consent was waived owing to the retrospective design of our study. Prior to analysis, all patient records were anonymized.