Identifying metabolite markers for preterm birth in cervicovaginal fluid by magnetic resonance spectroscopy

Abstract

Introduction: Preterm birth (PTB) may be preceded by changes in the vaginal microflora and metabolite profiles.

Objectives: We sought to characterise the metabolite profile of cervicovaginal fluid (CVF) of pregnant women by 1H NMR spectroscopy, and assess their predictive value for PTB.

Methods: A pair of high-vaginal swabs was obtained from pregnant women with no evidence of clinical infection and grouped as follows: asymptomatic low risk (ALR) women with no previous history of PTB, assessed at 20-22 gestational weeks, g.w., n = 83; asymptomatic high risk (AHR) women with a previous history of PTB, assessed at both 20-22 g.w., n = 71, and 26-28 g.w., n = 58; and women presenting with symptoms of preterm labor (PTL) (SYM), assessed at 24-36 g.w., n = 65. Vaginal secretions were dissolved in phosphate buffered saline and scanned with a 9.4 T NMR spectrometer.

Results: Six metabolites (lactate, alanine, acetate, glutamine/glutamate, succinate and glucose) were analysed. In all study cohorts vaginal pH correlated with lactate integral (r = -0.62, p < 0.0001). Lactate integrals were higher in the term ALR compared to the AHR (20-22 g.w.) women (p = 0.003). Acetate integrals were higher in the preterm versus term women for the AHR (20-22 g.w.) (p = 0.048) and SYM (p = 0.003) groups; and was predictive of PTB < 37 g.w. (AUC 0.78; 95 % CI 0.61-0.95), and delivery within 2 weeks of the index assessment (AUC 0.84; 95 % CI 0.64-1) in the SYM women, whilst other metabolites were not.

Conclusion: High CVF acetate integral of women with symptoms of PTL appears predictive of preterm delivery, as well as delivery within 2 weeks of presentation.

Keywords: Cervicovaginal fluid; Metabolites; Nuclear magnetic resonance (NMR); Pregnancy; Preterm birth.

Fig. 1

One dimensional ¹H NMR spectrum for metabolites observed in cervicovaginal fluid (CVF) samples and sterile swab (red). ppm parts per million (Color figure online)

Fig. 2

Data are presented as mean ± SE. Only one preterm delivery was recorded in the asymptomatic low risk group. ALR asymptomatic low risk women, AHR asymptomatic high risk women, SYM symptomatic women, g.w. gestation weeks. *p value <0.05 considered statistically significant (Color figure online)

Fig. 3

a Cervicovaginal fluid pH between the different cohorts. Box plots show the median line, with the box edges representing the 25 and 75 % quartiles. Whiskers extend to the furthermost value within 1.5 times the interquartile range from 25 to 75 % quartiles. b Vaginal fluid pH values versus normalized lactate integral, preterm and term groups. The correlation was virtually identical for all groups irrespective of delivery outcome, demonstrating that lactate contribute the most to pH. Black line represents a linear fit, r = −0.62, p < 0.0001. Red line represents a log₁₀ fit. pH range 3.6–6.1. ASYM asymptomatic women (ALR asymptomatic low risk and AHR 20–22 g.w. women) AHR asymptomatic high risk women, SYM symptomatic women, g.w. gestational weeks (Color figure online)

Fig. 4

Performance of acetate integrals in predicting preterm delivery in symptomatic pregnant women. a <37 g.w. b ≤32 g.w. c Within 2 weeks of index assessment. AUC area under the ROC curve