Elevated vaginal pH and neutrophils are associated strongly with early spontaneous preterm birth

OBJECTIVE: The purpose of this study was to determine the association of vaginal pH greater than or equal to5.0 and vaginal neutrophils >5 per oil-field with early preterm birth. STUDY DESIGN: This is a secondary analysis of the vaginal infections and prematurity cohort comprised of 13,917 women at 23 and 26 weeks of gestation. All women were tested for sexually transmitted infections and vaginal pH. Gram-stained smears were used for the detection of neutrophils. RESULTS: There were 5751 women (41.3%) with neutrophils >5 per oil-field and 2500 women (18.0%) with pH greater than or equal to5.0. Both elevated pH and neutrophils were present in 1149 women (8.3%). Neutrophils and pH were each significantly associated with spontaneous preterm birth, and the point estimate of the strength of that association increased as the gestational age at delivery decreased. CONCLUSION: Elevated vaginal pH and neutrophils are associated most strongly with the earliest preterm births.