Early pregnancy threshold vaginal pH and Gram stain scores predictive of subsequent preterm birth in asymptomatic women.

OBJECTIVE The study was undertaken to identify early pregnancy vaginal markers predictive of subsequent preterm birth. STUDY DESIGN In a multicenter Bacterial Vaginosis (BV) Trial, 21,554 women were screened with a vaginal pH and of these, two populations were studied. These included 12,041 who had a pregnancy outcome in the database and 6838 women who had a vaginal pH of 4.5 or greater and a Gram stain score and a pregnancy outcome in the database. ColorpHast Indicator Strips were used to determine the vaginal pH and the Nugent criteria were used to determine a vaginal Gram stain score of 0 to 10. RESULTS Delivery at <37, <35, or <32 weeks' gestation was similar for women with a vaginal pH of less than 4.4 or 4.7 (P not significant) but was increased in women with a pH of 5.0 (P =.04,.02,.03, respectively) or with a pH of 5.0 or greater (at each gestational age P <.0001). The effect of pH of 5.0 or greater was similar for women who had a spontaneous preterm birth at each gestational age (P <.0001) or birth weight of less than 2500 g or less than 1500 g (P <.0005). Women with a vaginal pH of 4.5 or greater and a Gram stain score of 9 to 10 (compared with 0-8) had increased preterm births at <37, <35, and <32 weeks' gestation (P <.01), and birth weights less than 2500 g (P <.0001) or less than 1500 g (P <.01). Women whose vaginal pH was 5.0 or greater had a higher prevalence of vaginal fetal fibronectin > or =50 ng/mL (P <.0001), but the proportion of women with a vaginal fetal fibronectin > or =50 mg/mL did not differ by Gram stain score. CONCLUSION Women with a vaginal pH of 5.0 or greater or a vaginal pH of 4.5 or greater and a Gram stain score of 9 to 10 had significantly increased preterm births at <37, <35, and 32 weeks' gestation and/or a birth weight less than 2500 g or less than 1500 g.