Association Of Vaginal Ph >5 At 13-20 Weeks Of Gestation With The Incidence Of Preterm Birth: A Prospective Cohort Study

Abstract

Introduction Preterm delivery remains the largest cause of neonatal mortality, accounting for 27% of the 3.1 million annual deaths worldwide. Maternal infection increases the incidence of and is responsible for 40% of spontaneous preterm deliveries making its prevention critical.Bacterial vaginosis is one of the major contributors to preterm birth with an incidence of 10-30% in all populations worldwide and 25% incidence in pregnant women.The most commonly utilized method of screening for Bacterial Vaginosis (BV) is the Amsel score. However, the procedure is difficult to reliably implement and unaffordable in rural, developing country primary health care centres. The vaginal pH acidity test is a simple, inexpensive procedure that can be easily administered in rural settings. The aim of this study is to assess whether vaginal pH > 5 is associated with an increased incidence of preterm birth. Methods The study was a prospective cohort study nested within the ongoing community based randomized controlled trial assessing the efficacy of oral Clindamycin for reducing the incidence of preterm birth implemented in 12 Primary Health Center areas of Belgaum and Bagalkot districts of Karnataka during the period of July 2015 to August 2016. The trial screened permanent residents in the study area who presented for antenatal care (ANC) at 13-20 weeks of gestation for vaginal pH by obtaining a sample of fluid from the posterior fornix of the vagina with pH paper. The study population for prospective cohort study was 5148 pregnant women. Women with vaginal pH ≥ 5 and randomized to the placebo arm (n=809 women) formed the exposed group while 4,339 women with vaginal pH < 5 formed the unexposed group. Results The incidence of preterm birth in the exposed group was 15.3% compared to 11.8% in the un-exposed group with an absolute difference in the rate of preterm birth being 3.5%. i.e. 23% greater risk of preterm birth in women with vaginal pH >5. On performing logistic regression analysis, there was a statistically significant correlation with reference to cut-off of vaginal pH > 5 with increased risk of spontaneous preterm birth, in both early (OR -1.489, 95% CI 1.131-1.961, p value-0.005) and overall (OR-1.372, 95% CI 1.11-1.69 p value-0.003) preterm birth. Conclusion Vaginal pH ≥ 5.0 is significantly associated with increased risk of preterm birth and maybe considered as a good predictor of both early (< 34 weeks) and overall (<37weeks) preterm birth