A prospective study of vaginal pH as a predictor of preterm delivery

Abstract

Objective: To test the usefulness of vaginal pH determinations in the prediction of the risk of preterm delivery at or before 36 weeks of gestation. Methods: This was a prospective study of asymptomatic pregnant women. Vaginal pH was determined using pH paper in a sterile speculum examination during prenatal visits. Patients were followed to delivery and hospital records were reviewed to extract obstetric information. A total of 308 women agreed to participate and met the criteria for enrolment. Preterm delivery was defined as delivery at or prior to 36 weeks of gestation. Abnormal pH was defined as a pH of > 5.0. Results: Abnormal vaginal pH was associated with increased risk of preterm delivery, (OR 3.3, 95% CI 1.15, 9.2; p = 0.02). In the first trimester, an abnormal vaginal pH was not associated with preterm delivery (p = 0.3). After the first trimester, a vaginal pH of 5.0 or greater was associated with increased risk of preterm delivery (OR 9.6, 95% CI 2.0, 45.5; p = 0.001) as well as delivering an infant of less than 2500 g (OR 3.1, 95% CI 1.2, 7.8; p = 0.015). History of a previous preterm delivery was associated with increased risk of preterm delivery (OR 6.2, 95% CI 1.6, 23.7; p = 0.02). A logistic regression model used to control for a history of preterm delivery and race showed abnormal vaginal pH to remain as an independent predictor of preterm delivery (p = 0.01). Conclusions: High vaginal pH (≥ 5.0) identified women at risk for preterm delivery.