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.