Clinical characteristics of the study population
We collected data on maternal characteristics, including age, parity, pre-pregnancy body mass index, history of preterm birth (PTB), plurality, infertility treatment (intrauterine insemination and in vitro fertilization [IVF]) of index pregnancy, gestational age at admission, diagnosis at admission (pPROM, IIOC, PTL, or short CL), and use of antibiotics before admission. Prior antibiotic treatment was defined as the use of antibiotics within 4 weeks prior to the vaginal culture test. Perinatal outcomes included gestational age at delivery, mode of delivery, abortion, stillbirth, histologic chorioamnionitis, sex, birth weight, Apgar score, neonatal mortality, neonatal intensive care unit admission rate, and neonatal sepsis. Abortion included all fetal loss in utero occurring before 20 weeks of gestation, while stillbirth included fetal loss occurring beyond 20 weeks of gestation with 5-min Apgar scores of 0. According to the protocol used by Redline et al.,15 histologic chorioamnionitis was reviewed by a single pathologist (JSK) as previously defined.16Early-onset neonatal sepsis (EONS) was defined as neonatal sepsis within the first 3 days of life, including infection by any kind of organism. Suspected sepsis was diagnosed clinically by pediatricians, while proven sepsis was diagnosed when microorganisms were isolated from the blood or cerebrospinal fluid of neonates.