Modified classification of Gram-stained vaginal smears to predict spontaneous preterm birth: a prospective cohort study

Abstract

The purpose of this study was to identify women at risk of spontaneous preterm birth through a 4-category Gram-stained vaginal smear method, not restricted to bacterial vaginosis. This was a prospective cohort study correlating Gram-stained vaginal smears in early pregnancy with spontaneous preterm birth. Smears were categorized as 'normal,' 'bacterial vaginosis-like,' 'grade I-like' (atypical gram-positive rods) or 'purulent grade I' (lactobacilli-dominated smears showing heavy leukorrhea of unknown cause). Normal microflora were associated with a 4-fold decreased risk (95%CI 0.1-0.6, P < .001) of spontaneous preterm birth and an abnormal Gram stain with an overall adjusted odds ratio of 5.2 (95%CI 1.8-14.5, P < .001). The sensitivity of vaginal smear diagnosis for preterm birth increased from 25% with conventional scoring up to 70% with these modified criteria. Accounting for atypical gram-positive bacteria and neutrophils on Gram-stained vaginal smears may identify a larger proportion of women at risk of preterm birth compared to diagnosis of bacterial vaginosis alone.